Thermostat Question
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From: In a 1995 M6 Coupe, speeding through Connecticut
Thermostat Question
I have a 1995 LT1 coupe with about 60,000 miles on it. When stopped at idle, the temp is pegging into the danger zone. When I drive, it comes back down.
I made sure there were no leaves blocking the radiator and that the fans are working properly, so I'm pretty sure I've got a bad thermostat and/or temperature sensor. Since they cost so little, I'm going to change both of them.
I read on the forums that I don't need to drain the system down to do a thermostat. When I started to open the thermostat housing, the coolant started coming out pretty fast so I immediately locked it back down to save the Optispark from any unneeded torture.
Do I need to drain the system down to do this, or was it because the engine was still a bit warm? It hadn't been driven in about 4 hours...but it was running very hot when it was driven. Or is there a trick I'm missing to take a little pressure off of the system?
I appreciate any thoughts you can provide.
I made sure there were no leaves blocking the radiator and that the fans are working properly, so I'm pretty sure I've got a bad thermostat and/or temperature sensor. Since they cost so little, I'm going to change both of them.
I read on the forums that I don't need to drain the system down to do a thermostat. When I started to open the thermostat housing, the coolant started coming out pretty fast so I immediately locked it back down to save the Optispark from any unneeded torture.
Do I need to drain the system down to do this, or was it because the engine was still a bit warm? It hadn't been driven in about 4 hours...but it was running very hot when it was driven. Or is there a trick I'm missing to take a little pressure off of the system?
I appreciate any thoughts you can provide.
Melting Slicks
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From: Indian Rocks Beach FL
St. Jude Donor '08-'09-'10
I drained about a gallon of coolant when I did mine. I'm pretty sure if there's anything in the expansion tank its going to dump out of the thermostat housing since the tank sits higher in the system. When you get it back together if it still has the same problem, check the temp using the digital guage function and compare the reading to the analog guage. They use different sensors and it's unlikely you'd have both go bad at the same time.
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From: In a 1995 M6 Coupe, speeding through Connecticut
Thanks. What's the best way to drain it? I haven't been under the car to check the radiator yet...but I assume there's a drain plug in the bottom. Is that the way to go?
Melting Slicks
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From: Indian Rocks Beach FL
St. Jude Donor '08-'09-'10
Yes, the drain petcock is on the bottom of the radiator on the passenger side. It should be just hand tight, don't overtighten when you close it. I understand they are fairly easy to break.
Le Mans Master
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From: Louisiana
What was the digital coolant temp when you notice the analog needle goes in the "danger zone" or hash marks? The analog guage goes over to the hash marks, eventhough the digital guage may say ~220* which is normal. Both my 95 and 92 do this.
I think you need to verify a few things before draining the coolant (unless it's time) or change the t-stat which is probably good. There are two different spots to get rid of air out of the LTx cars coolant system. One is on located next to the throttle body and the other next to the t-stat housing. If you do drain the coolant, the petcock is located on the passenger side bottom of the radiator. The cap has to be removed from the surge canister before draining coolant. To get the old coolant out of the block, you have to let the car warm up until the t-stat opens which should be 180-190*.
I think you need to verify a few things before draining the coolant (unless it's time) or change the t-stat which is probably good. There are two different spots to get rid of air out of the LTx cars coolant system. One is on located next to the throttle body and the other next to the t-stat housing. If you do drain the coolant, the petcock is located on the passenger side bottom of the radiator. The cap has to be removed from the surge canister before draining coolant. To get the old coolant out of the block, you have to let the car warm up until the t-stat opens which should be 180-190*.
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From: PORT JEFFERSON LONG ISLAND
you will need to remove the knock sensor to drain all the coolant from the block,no need to run the engine prior to draining the coolant just remove the pressure cap but make sure the engine is cool before you do anything.
Melting Slicks
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From: Indian Rocks Beach FL
St. Jude Donor '08-'09-'10
No need to drain all the coolant to change the thermostat, just use a clean catch bucket and you can reuse the collant. If you've got DexCool coolant (orange colored) do not use tap water to fill, distilled water or DexCool only.
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Le Mans Master
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From: Phoenix AZ
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hot car
if driving the car makes the temp come down, you need to consider two things, either your air flow is restricted, or you have extra air inthe engine, ie. bubbles, which your reverse flow engine was designed to overcome with it's advanced water distribution.
If making the car move through the air is cooling it, you have an air flow problem, either a slow moving fan caused by a bad fan, bad ground, or a bad fan relay with high resistance on the relay contacts.
If revvin up the engine is making it cool, maybe the impeller in the water pump is corroded, loose on the shaft, partially restricted, etc.
thermostat isn't the problem if it cools down, and the engine does cools down, so it's not the sensor.
a quick check of the sensor,place a thermometer, or temp sensor from your house in the garage, or from outside on your engine, and check it with the dash gauge when you first turn the key on before you start the engine.
If making the car move through the air is cooling it, you have an air flow problem, either a slow moving fan caused by a bad fan, bad ground, or a bad fan relay with high resistance on the relay contacts.
If revvin up the engine is making it cool, maybe the impeller in the water pump is corroded, loose on the shaft, partially restricted, etc.
thermostat isn't the problem if it cools down, and the engine does cools down, so it's not the sensor.
a quick check of the sensor,place a thermometer, or temp sensor from your house in the garage, or from outside on your engine, and check it with the dash gauge when you first turn the key on before you start the engine.
Last edited by coupeguy2001; Jul 28, 2007 at 11:53 PM.
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That analog gauge will be very close to "pegged" when the fans come on at approx. 220-228. But look very close at the analog gauge, and you'll see the needle is not quite into the shaded zone. At that same time, look at the digital gauge and see what it says. Probably in the 220-228 range, which is normal for a late model C4 sitting at a stop light.
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From: In a 1995 M6 Coupe, speeding through Connecticut
I put the new thermostat in this morning since it wouldn't hurt to have a new one.
I took it out for about 20 minutes of stop and go driving (avg. speed 35-40 mph) and the temp on the digital was between 200-220. I didn't use the A/C.
I came back and sat at idle for a while and watched the digital guage. It would go up to 237 before the fan came on. The fan would shut off when the temp came back down to about 225. Is that fan coming on at a higher temp than normal?
The other issue...I'm getting a low coolant light...but the overflow is full to the hot level. Would air in the system cause this?
I took it out for about 20 minutes of stop and go driving (avg. speed 35-40 mph) and the temp on the digital was between 200-220. I didn't use the A/C.
I came back and sat at idle for a while and watched the digital guage. It would go up to 237 before the fan came on. The fan would shut off when the temp came back down to about 225. Is that fan coming on at a higher temp than normal?
The other issue...I'm getting a low coolant light...but the overflow is full to the hot level. Would air in the system cause this?
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Yes, air in the system is known to cause this.
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From: In a 1995 M6 Coupe, speeding through Connecticut
Yep, when the A/C goes on the fans work great.
I guess I'll look into the higher temp fan start. Any idea what controls that?
Also...kind of a stupid question, but is it better to bleed the air from the system with the overflow cap on or off?
I guess I'll look into the higher temp fan start. Any idea what controls that?
Also...kind of a stupid question, but is it better to bleed the air from the system with the overflow cap on or off?
Le Mans Master
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From: One day you're a Comet...the next day you're dust... Arkansas
Did you mean lower temp fan start? It's controlled by the ECM. Do a search or get a manual. Lots of posts and arguments on this.
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From: Louisiana
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From: In a 1995 M6 Coupe, speeding through Connecticut
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From: In a 1995 M6 Coupe, speeding through Connecticut
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
If the fans are coming on only at very high temps, then check the temp sending unit for the computer, it may have lost its accuracy. This is assuming the digital guage isn't also fed by it. It's also possible it's fine and your dash guage is just reading high. The FSM should tell you what ohms correspond to what temperatures.
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From: The Top of Utah
Originally Posted by FFCus
I made sure there were no leaves blocking the radiator
RACE ON!!!