Ping: Dean, Gary, anyone else with insight
Question:
Just got back from the shop, t-stat was sticking, new one kept the gauge right at 200. Pressure test of the system showed no leaks, no collapsing hoses and that the WP was working PERFECTLY. They popped in the Delco t-stat I took with me, on the ride home (about 20 mins after they got the truck to operating temp.) it never budged off 200. The OE t-stat lasted 6 years and I only replaced it because I thought it was sticking open causing the truck to not warm up, turns out that the temp. sending unit was bad then, so I could have gotten more time out of it… – Hide quoted text — Show quoted text -> Mike, > Use a Stant/Gates/Robertshaw thermostat. The rest aren’t worth the box > they come. A dying water pump can cause the "overheat at speed > symptom" too. I’ve seen OEM pumps fail (loose enough efficiency to > cause overheating) in as little as 50k miles. A dying radiator cap can > also cause this. Again, use a Stant/Gates. > Cap was the first thing I replaced, it is a Stant. Since I already have > the part, and I’ll be sitting at the shop waiting for the truck, I think > I’ll stickwith the Delco t-stat, first one lasted me 80,000 miles. > Not likely to be the lower hose as if it collapses at speed the engine > will overheat in a heartbeat. But give it a squeeze anyway to make > sure the anti-collapse spring is in place. In any case, after 8 years > and 100k miles, new hoses wouldn’t hurt! > Another possibility is restricted airflow through the radiator. Unlike > the good old days, cooling systems are very marginal today. Inspect > the front as best you can for bent fins from bugs/debris. Also, spray > (gently) with a garden hose from the back of the radiator to the front > to remove any dirt that may accumulate. Note that if airflow is > restricted through the A/C condenser, it will be restricted through > the radiator as well. > Back-flushed the rad. and condesner, separately, to get bugs/debris out, > not too much in there. There are a couple bent fins on the condenser, > not too many though. > Have you been removing the block drains when you change coolant? Rust > and scale can build up in the bottom of the water jacket and cause a > very gradual (over the years type gradual) loss of cooling efficiency. > I’ve done one coolant flush since the rad. has been replaced, as another > try at fixing this darn problem. I got a power flush done since at > times I’m just too lazy to do the work myself. I’m also not sure I > could even get the block drains out without pulling the engine or > removing a lot of stuff. > Finally, a small leak can result in air being sucked into the cooling > system as it cools. So now you have an air bubble which usually causes > erratic temperature indications but might result in the symptom you > have. A pressure test should reveal any leak. > No visible leaks, even after it’s sat for a while. Of course, I don’t > go crawling on the ground, in the dark, after work to see if there’s a > drip someplace that I didn’t see. > Let us know what you find. > Dean > Thanks for the tips. >> I have a 94 GMC Jimmy 4-door 4×4. This spring and summer the truck >> has been running warmer than it used to (digital dash gauge showed >> 200 normally, has shown ~220 more this year, one bar up from 200). >> I’m taking it to my shop tomorrow to at least have the t-stat >> replaced, have any of you SEEN where it is on a CPI equipped 4.3, >> it’s a bear to get to. >> On my way to work today, in ~80* weather, it got to 220 when I was >> traveling at 55-60, and took a while to get to 220, like 4 miles, >> cooled down when I slowed down for the lower speed limit roads. On >> my way home, it was the opposite, same roads, warmed up to 220 faster >> on the slower roads, then went down to 200 and stayed down when I got >> on the 55 road and then back down to slower roads. >> I’ve been thinking it was a stuck t-stat all along, though a failing >> water pump is also possible >> Rad. is less than 2 years old, copper core SDI (I think), WP is less >> than 3 years old. I think the fan and fan clutch are less than 3 as >> well, t-stat is less than 2 years old, but it’s an A/M, guy at the >> dealer said the best luck he’s had with t-stats were with AC-Delco’s, >> and I was there for the gasket anyway, since the parts stores say I >> don’t need one, so I got that one, a 195 unit, and that’s what’s in >> there now. Coolant temp. sending unit (for the dash gauge) is less >> than 2 years old as well. Hoses are still the originals I think, >> truck has 101,600 on it, so it could be a collapsing hose, but not >> the way it’s acting. >> I know this was long, just wanted to give a little background. Truck >> goes to my favorite shop (and I know I’m their favorite customer, >> $11,000 in repairs from 2 accidents plus a gas tank and various >> others I didn’t want to tackle), so they can hook it to the computer >> to see what the CTS says the temp is.
Response:
> Mike, > Use a Stant/Gates/Robertshaw thermostat. The rest aren’t worth the box > they come. A dying water pump can cause the "overheat at speed symptom" > too. I’ve seen OEM pumps fail (loose enough efficiency to cause > overheating) in as little as 50k miles. A dying radiator cap can also > cause this. Again, use a Stant/Gates.
Cap was the first thing I replaced, it is a Stant. Since I already have the part, and I’ll be sitting at the shop waiting for the truck, I think I’ll stickwith the Delco t-stat, first one lasted me 80,000 miles. > Not likely to be the lower hose as if it collapses at speed the engine > will overheat in a heartbeat. But give it a squeeze anyway to make sure > the anti-collapse spring is in place. In any case, after 8 years and > 100k miles, new hoses wouldn’t hurt! > Another possibility is restricted airflow through the radiator. Unlike > the good old days, cooling systems are very marginal today. Inspect the > front as best you can for bent fins from bugs/debris. Also, spray > (gently) with a garden hose from the back of the radiator to the front > to remove any dirt that may accumulate. Note that if airflow is > restricted through the A/C condenser, it will be restricted through the > radiator as well.
Back-flushed the rad. and condesner, separately, to get bugs/debris out, not too much in there. There are a couple bent fins on the condenser, not too many though. > Have you been removing the block drains when you change coolant? Rust > and scale can build up in the bottom of the water jacket and cause a > very gradual (over the years type gradual) loss of cooling efficiency.
I’ve done one coolant flush since the rad. has been replaced, as another try at fixing this darn problem. I got a power flush done since at times I’m just too lazy to do the work myself. I’m also not sure I could even get the block drains out without pulling the engine or removing a lot of stuff. > Finally, a small leak can result in air being sucked into the cooling > system as it cools. So now you have an air bubble which usually causes > erratic temperature indications but might result in the symptom you > have. A pressure test should reveal any leak.
No visible leaks, even after it’s sat for a while. Of course, I don’t go crawling on the ground, in the dark, after work to see if there’s a drip someplace that I didn’t see. > Let us know what you find. > Dean
Thanks for the tips. – Hide quoted text — Show quoted text -> I have a 94 GMC Jimmy 4-door 4×4. This spring and summer the truck > has been running warmer than it used to (digital dash gauge showed 200 > normally, has shown ~220 more this year, one bar up from 200). I’m > taking it to my shop tomorrow to at least have the t-stat replaced, > have any of you SEEN where it is on a CPI equipped 4.3, it’s a bear to > get to. > On my way to work today, in ~80* weather, it got to 220 when I was > traveling at 55-60, and took a while to get to 220, like 4 miles, > cooled down when I slowed down for the lower speed limit roads. On my > way home, it was the opposite, same roads, warmed up to 220 faster on > the slower roads, then went down to 200 and stayed down when I got on > the 55 road and then back down to slower roads. > I’ve been thinking it was a stuck t-stat all along, though a failing > water pump is also possible > Rad. is less than 2 years old, copper core SDI (I think), WP is less > than 3 years old. I think the fan and fan clutch are less than 3 as > well, t-stat is less than 2 years old, but it’s an A/M, guy at the > dealer said the best luck he’s had with t-stats were with AC-Delco’s, > and I was there for the gasket anyway, since the parts stores say I > don’t need one, so I got that one, a 195 unit, and that’s what’s in > there now. Coolant temp. sending unit (for the dash gauge) is less > than 2 years old as well. Hoses are still the originals I think, > truck has 101,600 on it, so it could be a collapsing hose, but not the > way it’s acting. > I know this was long, just wanted to give a little background. Truck > goes to my favorite shop (and I know I’m their favorite customer, > $11,000 in repairs from 2 accidents plus a gas tank and various others > I didn’t want to tackle), so they can hook it to the computer to see > what the CTS says the temp is.
Response:
Mike, Use a Stant/Gates/Robertshaw thermostat. The rest aren’t worth the box they come. A dying water pump can cause the "overheat at speed symptom" too. I’ve seen OEM pumps fail (loose enough efficiency to cause overheating) in as little as 50k miles. A dying radiator cap can also cause this. Again, use a Stant/Gates. Not likely to be the lower hose as if it collapses at speed the engine will overheat in a heartbeat. But give it a squeeze anyway to make sure the anti-collapse spring is in place. In any case, after 8 years and 100k miles, new hoses wouldn’t hurt! Another possibility is restricted airflow through the radiator. Unlike the good old days, cooling systems are very marginal today. Inspect the front as best you can for bent fins from bugs/debris. Also, spray (gently) with a garden hose from the back of the radiator to the front to remove any dirt that may accumulate. Note that if airflow is restricted through the A/C condenser, it will be restricted through the radiator as well. Have you been removing the block drains when you change coolant? Rust and scale can build up in the bottom of the water jacket and cause a very gradual (over the years type gradual) loss of cooling efficiency. Finally, a small leak can result in air being sucked into the cooling system as it cools. So now you have an air bubble which usually causes erratic temperature indications but might result in the symptom you have. A pressure test should reveal any leak. Let us know what you find. Dean – Hide quoted text — Show quoted text -> I have a 94 GMC Jimmy 4-door 4×4. This spring and summer the truck > has been running warmer than it used to (digital dash gauge showed 200 > normally, has shown ~220 more this year, one bar up from 200). I’m > taking it to my shop tomorrow to at least have the t-stat replaced, > have any of you SEEN where it is on a CPI equipped 4.3, it’s a bear to > get to. > On my way to work today, in ~80* weather, it got to 220 when I was > traveling at 55-60, and took a while to get to 220, like 4 miles, > cooled down when I slowed down for the lower speed limit roads. On my > way home, it was the opposite, same roads, warmed up to 220 faster on > the slower roads, then went down to 200 and stayed down when I got on > the 55 road and then back down to slower roads. > I’ve been thinking it was a stuck t-stat all along, though a failing > water pump is also possible > Rad. is less than 2 years old, copper core SDI (I think), WP is less > than 3 years old. I think the fan and fan clutch are less than 3 as > well, t-stat is less than 2 years old, but it’s an A/M, guy at the > dealer said the best luck he’s had with t-stats were with AC-Delco’s, > and I was there for the gasket anyway, since the parts stores say I > don’t need one, so I got that one, a 195 unit, and that’s what’s in > there now. Coolant temp. sending unit (for the dash gauge) is less > than 2 years old as well. Hoses are still the originals I think, > truck has 101,600 on it, so it could be a collapsing hose, but not the > way it’s acting. > I know this was long, just wanted to give a little background. Truck > goes to my favorite shop (and I know I’m their favorite customer, > $11,000 in repairs from 2 accidents plus a gas tank and various others > I didn’t want to tackle), so they can hook it to the computer to see > what the CTS says the temp is.
Response:
I have a 94 GMC Jimmy 4-door 4×4. This spring and summer the truck has been running warmer than it used to (digital dash gauge showed 200 normally, has shown ~220 more this year, one bar up from 200). I’m taking it to my shop tomorrow to at least have the t-stat replaced, have any of you SEEN where it is on a CPI equipped 4.3, it’s a bear to get to. On my way to work today, in ~80* weather, it got to 220 when I was traveling at 55-60, and took a while to get to 220, like 4 miles, cooled down when I slowed down for the lower speed limit roads. On my way home, it was the opposite, same roads, warmed up to 220 faster on the slower roads, then went down to 200 and stayed down when I got on the 55 road and then back down to slower roads. I’ve been thinking it was a stuck t-stat all along, though a failing water pump is also possible Rad. is less than 2 years old, copper core SDI (I think), WP is less than 3 years old. I think the fan and fan clutch are less than 3 as well, t-stat is less than 2 years old, but it’s an A/M, guy at the dealer said the best luck he’s had with t-stats were with AC-Delco’s, and I was there for the gasket anyway, since the parts stores say I don’t need one, so I got that one, a 195 unit, and that’s what’s in there now. Coolant temp. sending unit (for the dash gauge) is less than 2 years old as well. Hoses are still the originals I think, truck has 101,600 on it, so it could be a collapsing hose, but not the way it’s acting. I know this was long, just wanted to give a little background. Truck goes to my favorite shop (and I know I’m their favorite customer, $11,000 in repairs from 2 accidents plus a gas tank and various others I didn’t want to tackle), so they can hook it to the computer to see what the CTS says the temp is.
