1993 4.3L Vortec Cooling System Mystery – A Novel
Question:
I have a baffling cooling system problem with my 1993 Oldsmobile Bravada. It is almost, but not quite, overheating… This S.U.V. (virtually the same vehicle as the Chevy S-10 Blazer and GMC S-15 Jimmy) has a 4.3-liter Vortec V-6 with approximately 132,000 total miles. Pertinent (?) to my particular automotive conundrum: It is equipped with air conditioning. Bear with me: this gets complicated. A few weeks ago I noticed a small amount (mere drops) of coolant underneath the vehicle. I correctly deduced that it was coming from the weep hole beneath the water pump and had it replaced with a newly-manufactured (not re-built) GMB-brand pump. This stopped the leaking problem, but opened up a whole new can of worms… Always before, the engine operating temperature had been rock-steady at 210 degrees Fahrenheit (according to the gauge on the instrument panel), whether the engine was at cruising speed or idling. Even on the rare occasions when I have hauled a trailer the temperature did not get much higher than 215 or so… Now, after replacing the water pump, the operating temperature reached as high as 235 degrees, which in my humble estimation is on the borderline of overheating. Curiously enough, the highest temperatures occur when driving — when the engine idles the temperature usually drops back to around 215 degrees or thereabouts. OK, I thought, the thermostat must be bad. I replaced the thermostat with an identical part (made by Stant, 195-degree) and experienced no change in symptoms. Hmmmm… Next step was to flush the cooling system several times. I drained the system, used a jug of Prestone’s "Super Flush," drove the recommended amount and then flushed the system out three times with plain water before re-filling the system with a 50-50 coolant mix. No change in operating temperature. Suspecting a faulty fan clutch, I examined it and found nothing apparently amiss; in fact, when the engine is on and up to temperature, one can feel a considerable volume of air being moved. Bewildered now, I disassembled the old water pump (the one that had been leaking) and examined the inside. It was remarkably clean after 130,000+ miles. I then removed the new water pump and disassembled it to ensure that it was equipped with a reverse impeller (which is required). Comparing the two, I noticed two small, apparently inconsequential, differences: the new pump was a rougher casting, both inside and outside, and it also had a threaded plug in the top (apparently some applications require this hole for a heater hose or other such purpose). I then replaced the gaskets, closed everything up with RTV sealant and reassembled. No change in symptoms. Because I had $15 I didn’t need, I replaced the coolant temperature sending unit. No change. The whole cooling problem had started after I replaced the water pump, so, grasping at straws, I purchased another water pump (a re-manufactured GM casting this time) and installed it. I noticed a very minor improvement in operating temperature, but again, when the vehicle is at highway speed, the temperature creeps up, way above what the normal operating temperature used to be (210 deg F). I know (or am convinced I know) that the problem is not a faulty gauge — once, when travelling up a lengthy hill at highway speed, the indicated temperature was in excess of 235 degrees and the "Check Gauges" light came on… As soon as I decelerated and coasted down the far side of the hill the engine temp dropped below 235 and the light went out, right where one would expect it to… Some in another newsgroup (rec.autos.tech — forgive me if you have seen this posting there already) have suggested an air bubble in the system, which seems logical, but how do you get something like that out of the system? There is no bleeder fitting on the vehicle (is there?), so I parked the vehicle facing uphill on a *very* steep incline and ran it without the radiator cap, hoping that the bubble would work its way to the top of the radiator. Not sure if that helped at all… Another opinion from rec.autos.tech: >>It sounds like you have a restriction in flow. I had the EXACT same problem,
replaced the water pump and every time I drove up the hill to work it turned on the "check gauges" light, after going thru the radiator and the pump and thermo I realized it was the heater fitting at the intake manifold. I had changed that at the same time as the pump and some heater fittings have different restrictors than others. If you didn’t replace the fitting it is possible that a piece of material plugged the fitting. If you haven’t replaced the fitting yet you should because they have a habit of deteriorating and breaking off, leaving you to pull the intake and chisel and tap out the hole. When checking the fitting, check that the heater core isn’t plugged, remove the heater fitting restrictor and see if that helps.<<< That didn’t seem logical to me, as not very much coolant is circulated through the heater core… I haven’t replaced that fitting and don’t intend to; it is still in excellent condition — no surface rust at all. Also, it is winter here in Maine and I would notice if the heater weren’t working well! Still another voice from rec.autos.tech: >>I have had a similar problem with my 1992 S10 with the 4.3 V6. What
triggered mine was replacing the heater tube coming from the rear of the engine. I had the radiator rodded out, replaced the thermostat, rad. cap, hoses, belts, and it still climbed to the top of the gauge. But, a few days ago, the needle started to stay in the middle, and as a test, I drove it up the I-15 through the Cajon pass at 80+ MPH in 3rd (OD auto) all the way to the top — it’s a steep grade that goes for about 15 miles or so — and the needle stayed below the middle. Only when I first head to work in the morning does the temp skyrocket, but it drops to the middle a few minutes after. I have no clue what caused this, I figured it was a temp sensor… maybe it’s the gauge. Just wanted to let ya know you’re not alone, and maybe it’ll go away (bad thing to say about overheating engine).<<< I don’t think I am naive enough to think that a problem like this will just go away by itself… I’m out of ideas here. There is plenty of oil in the vehicle, ample coolant, nothing blocking the radiator grille… What’s the deal? Help! Thanks in advance for any assistance you may be able to provide, BRBowden
Response:
To bleed the possible air bubbles out, turn the heater on hottest setting and crack open highest fitting on the vehicle ( usually the heater hose to heater core connection at the firewall) and let it run a while . When the water pump was replaced, they didn’t put in a new thermostat did they? I don’t know how long you’ve had the truck but perhaps a previous owner installed a cooler thermostat, and you or your mechanic replaced it with the stock ( hotter ) thermostat. Also check the thermostat for proper operation. I do this with a meat thermometer and a pan of water on the stove before installing.
– Hide quoted text — Show quoted text ->I have a baffling cooling system problem with my 1993 Oldsmobile Bravada. It is >almost, but not quite, overheating… This S.U.V. (virtually the same vehicle >as the Chevy S-10 Blazer and GMC S-15 Jimmy) has a 4.3-liter Vortec V-6 with >approximately 132,000 total miles. Pertinent (?) to my particular automotive >conundrum: It is equipped with air conditioning. Bear with me: this gets >complicated. >A few weeks ago I noticed a small amount (mere drops) of coolant underneath the >vehicle. I correctly deduced that it was coming from the weep hole beneath the >water pump and had it replaced with a newly-manufactured (not re-built) >GMB-brand pump. This stopped the leaking problem, but opened up a whole new can >of worms… >Always before, the engine operating temperature had been rock-steady at 210 >degrees Fahrenheit (according to the gauge on the instrument panel), whether >the engine was at cruising speed or idling. Even on the rare occasions when I >have hauled a trailer the temperature did not get much higher than 215 or so… >Now, after replacing the water pump, the operating temperature reached as high >as 235 degrees, which in my humble estimation is on the borderline of >overheating. Curiously enough, the highest temperatures occur when driving — >when the engine idles the temperature usually drops back to around 215 degrees >or thereabouts. >OK, I thought, the thermostat must be bad. I replaced the thermostat with an >identical part (made by Stant, 195-degree) and experienced no change in >symptoms. Hmmmm… >Next step was to flush the cooling system several times. I drained the system, >used a jug of Prestone’s "Super Flush," drove the recommended amount and then >flushed the system out three times with plain water before re-filling the >system with a 50-50 coolant mix. No change in operating temperature. >Suspecting a faulty fan clutch, I examined it and found nothing apparently >amiss; in fact, when the engine is on and up to temperature, one can feel a >considerable volume of air being moved. >Bewildered now, I disassembled the old water pump (the one that had been >leaking) and examined the inside. It was remarkably clean after 130,000+ >miles. I then removed the new water pump and disassembled it to ensure that it >was equipped with a reverse impeller (which is required). Comparing the two, I >noticed two small, apparently inconsequential, differences: the new pump was a >rougher casting, both inside and outside, and it also had a threaded plug in >the top (apparently some applications require this hole for a heater hose or >other such purpose). I then replaced the gaskets, closed everything up with RTV >sealant and reassembled. No change in symptoms. >Because I had $15 I didn’t need, I replaced the coolant temperature sending >unit. No change. >The whole cooling problem had started after I replaced the water pump, so, >grasping at straws, I purchased another water pump (a re-manufactured GM >casting this time) and installed it. I noticed a very minor improvement in >operating temperature, but again, when the vehicle is at highway speed, the >temperature creeps up, way above what the normal operating temperature used to >be (210 deg F). >I know (or am convinced I know) that the problem is not a faulty gauge — once, >when travelling up a lengthy hill at highway speed, the indicated temperature >was in excess of 235 degrees and the "Check Gauges" light came on… As soon as >I decelerated and coasted down the far side of the hill the engine temp dropped >below 235 and the light went out, right where one would expect it to… >Some in another newsgroup (rec.autos.tech — forgive me if you have seen this >posting there already) have suggested an air bubble in the system, which seems >logical, but how do you get something like that out of the system? There is no >bleeder fitting on the vehicle (is there?), so I parked the vehicle facing >uphill on a *very* steep incline and ran it without the radiator cap, hoping >that the bubble would work its way to the top of the radiator. Not sure if >that helped at all… >Another opinion from rec.autos.tech: >>>It sounds like you have a restriction in flow. I had the EXACT same problem, >replaced the water pump and every time I drove up the hill to work it turned on >the "check gauges" light, after going thru the radiator and the pump and thermo >I realized it was the heater fitting at the intake manifold. I had changed that >at the same time as the pump and some heater fittings have different >restrictors than others. If you didn’t replace the fitting it is possible that >a piece of material plugged the fitting. If you haven’t replaced the fitting >yet you should because they have a habit of deteriorating and breaking off, >leaving you to pull the intake and chisel and tap out the hole. When checking >the fitting, check that the heater core isn’t plugged, remove the heater >fitting restrictor and see if that helps.<<< >That didn’t seem logical to me, as not very much coolant is circulated through >the heater core… I haven’t replaced that fitting and don’t intend to; it is >still in excellent condition — no surface rust at all. Also, it is winter >here in Maine and I would notice if the heater weren’t working well! >Still another voice from rec.autos.tech: >>>I have had a similar problem with my 1992 S10 with the 4.3 V6. What >triggered mine was replacing the heater tube coming from the rear of the >engine. I had the radiator rodded out, replaced the thermostat, rad. cap, >hoses, belts, and it still climbed to the top of the gauge. But, a few days >ago, the needle started to stay in the middle, and as a test, I drove it up the >I-15 through the Cajon pass at 80+ MPH in 3rd (OD auto) all the way to the top >– it’s a steep grade that goes for about 15 miles or so — and the needle >stayed below the middle. Only when I first head to work in the morning does the >temp skyrocket, but it drops to the middle a few minutes after. I have no clue >what caused this, I figured it was a temp sensor… maybe it’s the gauge. Just >wanted to let ya know you’re not alone, and maybe it’ll go away (bad thing to >say about overheating engine).<<< >I don’t think I am naive enough to think that a problem like this will just go >away by itself… >I’m out of ideas here. There is plenty of oil in the vehicle, ample coolant, >nothing blocking the radiator grille… What’s the deal? >Help! >Thanks in advance for any assistance you may be able to provide, >BRBowden
Response:
>>>When the water pump was replaced, they didn’t put in a new thermostat did
they?<<< Well, yes — I did replace the thermostat after seeing that the operating temperature was higher than before. I checked the old thermostat against the new and they were identical (195 degrees). >> I don’t know how long you’ve had the truck but perhaps a previous owner
installed a cooler thermostat, and you or your mechanic replaced it with the stock (hotter) thermostat.<<< I have had the truck going on three years now; that is why the operating temperature is baffling me — it had always been a rock-steady 210. >>Also check the thermostat for proper operation. I do this with a meat
thermometer and a pan of water on the stove before installing.<<< I don’t think a faulty thermostat is indicated here — the new one is behaving exactly as the old one did, leading me to believe that the problem is coming from somewhere else. In any event, the solution to this will have to wait another day or two — latest repair is the fuel pump, which went out on me yesterday. Talk about a pain in the neck! Hey, GM — how about putting an access panel in the cargo area so we can get to your electric fuel pumps when they invariably fail??!! To make matters worse, the fuel lines on top of the tank were a little rusty and in the process of trying to turn wrenches in the limited space available, I twisted one of the fittings off the fuel sending assembly. About $200 to replace that, plus another $70 for the fuel pump itself. <sigh> Like they say, "If it has boobs or wheels, it will give you trouble." Thanks for your response. BRB
Response:
it looks like some of these guys are not reading the original post….. I have a 92 s10 and a 93 blazer both with 4.3….they both run exactly at 210 on the gauge……I have not changed the water pump on either, but I have changed many pumps on other cars. From your explanation, the problem seems to be the pump design….I have always looked at the old pump/new pump when I put them on, and most of the time, the new pump has a bigger impeller, more of a fan than a gear….which should increase flow rate….and should not change the running temp of the engine…but if the engine is hot (THERMOSTAT OPEN), and the pump is pushing the water through the rad too fast, so that it does not have a chance to get cooled, the hot water is returned to the engine, where it gets heated even hotter, through the pump again, into the rad (flowing too fast to stay there and get I hope you follow this…this is what can happen when the thermostat is removed…..the coolant will not have a chance to get cooled by being locked in the radiator momentarily,,,,,,this causes overheating on the HIGHWAY, and not in the city……I know it sounds a little weird, but this is what happens….sometimes… I forgot to ask…you are using a 50/50 mix of antifreeze and water???? Check the fan clutch…..with a cold engine, feel the spinning resistance…..MAKE SURE THE KEY IS OUT OF THE IGNITION….then run the motor for 2 minutes….again check the resistance…it should have a little more resistance…..then check the resistance with the engine at full operating them….it should be hard to turn….indicating full resistance/locked and pulling max air into the rad… The air bubble is a good theory…..it happened to me….my s10…I changed the antifreeze and flushed the system….then drove the truck for about 3 months (everything fine)…then it was about 35 degrees and I was sitting in the truck with it idling and the heater on, waiting for a class, when I noticed the check gauges light, and the temp was way too high….. I shut off the engine, let it cool, and noticed the coolant was low….filled it and have not had the problem since….my dad told me after changing the antifreeze, drive it until it gets hot and re check the antifreeze every couple days after a come with very big radiators…..it almost never gets hot by idling…. By the way…I want to know what everyone is getting for their oil pressure on 4.3 CPI engines….mine while driving is around 40…stopped is around 25……on my s10 (TBI)…it gets around 70 or 80 driving and 40 stopped…..why the difference….they run the same oil and have the same mileage….but the CPI is in a blazer 4×4 with under the hood oil filter and oil cooler in the radiator….should this change the pressure???? Thanks…. – Hide quoted text — Show quoted text ->>>When the water pump was replaced, they didn’t put in a new thermostat did >they?<<< >Well, yes — I did replace the thermostat after seeing that the operating >temperature was higher than before. I checked the old thermostat against the >new and they were identical (195 degrees). >>> I don’t know how long you’ve had the truck but perhaps a previous owner >installed a cooler thermostat, and you or your mechanic replaced it with the >stock (hotter) thermostat.<<< >I have had the truck going on three years now; that is why the operating >temperature is baffling me — it had always been a rock-steady 210. >>>Also check the thermostat for proper operation. I do this with a meat >thermometer and a pan of water on the stove before installing.<<< >I don’t think a faulty thermostat is indicated here — the new one is behaving >exactly as the old one did, leading me to believe that the problem is coming >from somewhere else. >In any event, the solution to this will have to wait another day or two — >latest repair is the fuel pump, which went out on me yesterday. Talk about a >pain in the neck! Hey, GM — how about putting an access panel in the cargo >area so we can get to your electric fuel pumps when they invariably fail??!! To >make matters worse, the fuel lines on top of the tank were a little rusty and >in the process of trying to turn wrenches in the limited space available, I >twisted one of the fittings off the fuel sending assembly. About $200 to >replace that, plus another $70 for the fuel pump itself. <sigh> >Like they say, "If it has boobs or wheels, it will give you trouble." >Thanks for your response. >BRB
Response:
The CPI is the same I’m getting in my 94 Jimmy with the CPI engine. 40 while moving, 25 or so at idle once it’s warm. – Hide quoted text — Show quoted text – > it looks like some of these guys are not reading the original > post….. I have a 92 s10 and a 93 blazer both with 4.3….they both > run exactly at 210 on the gauge……I have not changed the water pump > on either, but I have changed many pumps on other cars. From your > explanation, the problem seems to be the pump design….I have always > looked at the old pump/new pump when I put them on, and most of the > time, the new pump has a bigger impeller, more of a fan than a > gear….which should increase flow rate….and should not change the > running temp of the engine…but if the engine is hot (THERMOSTAT > OPEN), and the pump is pushing the water through the rad too fast, so > that it does not have a chance to get cooled, the hot water is > returned to the engine, where it gets heated even hotter, through the > pump again, into the rad (flowing too fast to stay there and get > I hope you follow this…this is what can happen when the thermostat > is removed…..the coolant will not have a chance to get cooled by > being locked in the radiator momentarily,,,,,,this causes overheating > on the HIGHWAY, and not in the city……I know it sounds a little > weird, but this is what happens….sometimes… > I forgot to ask…you are using a 50/50 mix of antifreeze and > water???? > Check the fan clutch…..with a cold engine, feel the spinning > resistance…..MAKE SURE THE KEY IS OUT OF THE IGNITION….then run > the motor for 2 minutes….again check the resistance…it should have > a little more resistance…..then check the resistance with the engine > at full operating them….it should be hard to turn….indicating full > resistance/locked and pulling max air into the rad… > The air bubble is a good theory…..it happened to me….my s10…I > changed the antifreeze and flushed the system….then drove the truck > for about 3 months (everything fine)…then it was about 35 degrees > and I was sitting in the truck with it idling and the heater on, > waiting for a class, when I noticed the check gauges light, and the > temp was way too high….. I shut off the engine, let it cool, and > noticed the coolant was low….filled it and have not had the problem > since….my dad told me after changing the antifreeze, drive it until > it gets hot and re check the antifreeze every couple days after a > come with very big radiators…..it almost never gets hot by > idling…. > By the way…I want to know what everyone is getting for their oil > pressure on 4.3 CPI engines….mine while driving is around > 40…stopped is around 25……on my s10 (TBI)…it gets around 70 or > 80 driving and 40 stopped…..why the difference….they run the same > oil and have the same mileage….but the CPI is in a blazer 4×4 with > under the hood oil filter and oil cooler in the radiator….should > this change the pressure???? > Thanks…. >>>>When the water pump was replaced, they didn’t put in a new thermostat did >they?<<< >Well, yes — I did replace the thermostat after seeing that the operating >temperature was higher than before. I checked the old thermostat against the >new and they were identical (195 degrees). >>>> I don’t know how long you’ve had the truck but perhaps a previous owner >installed a cooler thermostat, and you or your mechanic replaced it with the >stock (hotter) thermostat.<<< >I have had the truck going on three years now; that is why the operating >temperature is baffling me — it had always been a rock-steady 210. >>>>Also check the thermostat for proper operation. I do this with a meat >thermometer and a pan of water on the stove before installing.<<< >I don’t think a faulty thermostat is indicated here — the new one is behaving >exactly as the old one did, leading me to believe that the problem is coming >from somewhere else. >In any event, the solution to this will have to wait another day or two — >latest repair is the fuel pump, which went out on me yesterday. Talk about a >pain in the neck! Hey, GM — how about putting an access panel in the cargo >area so we can get to your electric fuel pumps when they invariably fail??!! To >make matters worse, the fuel lines on top of the tank were a little rusty and >in the process of trying to turn wrenches in the limited space available, I >twisted one of the fittings off the fuel sending assembly. About $200 to >replace that, plus another $70 for the fuel pump itself. <sigh> >Like they say, "If it has boobs or wheels, it will give you trouble." >Thanks for your response. >BRB
Response:
>>>…most of the time, the new pump has a bigger impeller…<<<
In my case, the aftermarket impeller was the exact same size and construction (I opened the panel on the back and looked.). Next time I will avoid GMB aftermarket water pumps… >>I forgot to ask…you are using a 50/50 mix of antifreeze and water?<<<
A little thicker, but not much. Checked it with handy-dandy Prestone-brand measuring gadget & I’m protected to a little more than -40 (the end of the scale), so I figure I have a 60/40 coolant/water mix… I live in Maine & the prospect of a -40 degree day is not out of the question (It’s -4 outside as I write this…). >>Check the fan clutch…<<<
Fan clutch checks good… Also, oil pressure in my 4.3 TBI varies, depending on how long it’s been since an oil change, but ususally highway pressure is 50 or so, with idle pressure at 25-30… Thanks for your response. BRB
Response:
I read your problems on the newsgroup. what usually cause this running overhaet cindition like you describe is a worn out lower radiator hose. This hose feeds the pump and has a wire inserted to keep the hose from colaping when the pump is sucking hard. when the wire deteriorates the hose goes into partial colapes under driving conditions. You will not see this with the car parked. Squeze the hose for its full length to see if any portion can be collapesed by hand. This is most likely your problem. replace the hose and the overheat condition will go away. The new pump with its higher demand for input triggered the demise of the hose. If this fixes let me know. //greg
Response:
>I have a baffling cooling system problem with my 1993 Oldsmobile Bravada. It >is >almost, but not quite, overheating…
I have two little nuggets of advice for you. Check under the truck to see if your lower air damn didnt break off. Lots of vehicles have a plastic deflector that directs air into the radiator, this is particularly important while driving and will make the vehicle run warmer while moving than while sitting at idle. To tell you the truth I am not even sure your vehicle came with one but its worth checking into. The other thing that it could be is a "cylinder to coolant" head gasket leak begining to show its ugly head. There is a product called "block tester" that can detect exhaust in your coolant system. Its sold at NAPA stores and is very easy to use. This is unfotunately a very common symptom with beginning head problems. If you have any other questions please feel free to Email them to me.
