1992 Lt1 temperature running very high

**rolinger** · 10-06-11, 11:32 PM

Hello all.

About 2 months ago my 92 blew the lead hose (exiting the engine) to the radiator. I replaced the hose, added my own coolant mixture (50/50) and afterward the car was running high. Prior to this event the car around 180 regularly, occasionally creeping up to 195. Following this event the car ran over 220. I then went to the shop and had them flush the whole system and refill. The car continues to run very high and has been running around 230 as of late. Today it crept up to 236 on a relatively cool (75 degree) evening. Basically, the car is running 50 degrees hotter than it was before the hose blew and its running at what I think is a dangerously high temp. I constantly drive with one eye on the road and the other on the cars temperature; with one eye on the temp it means I don't have two on the road.

In addition, over the last several weeks, the "add coolant" light keeps coming on when I start the car and stays on for about 5min then it goes off. I have checked the levels continuously and theres plenty of 50/50 fluid in there. It seems the 'add coolant' light comes on when the car is cold - this never happened prior to the hose bursting.

I suspect the thermostat has gone bad. Are both issues related to a bad thermostat? What else need I look at? I am not much of a gear head, and know enough to fix basic things and such, but I want to fix this myself before trying to send to the mechanic.

Thoughts?

Ohh...what is that screw/bolt on the neck of the thermostat housing - I can't find any reference to its purpose and I have never seen that before.

Thanks,
-Russel

**rolinger** · 10-07-11, 08:21 AM

What I don't understand is why my car has been running around 180 for the better part of 14 years and now. After the hose burst, and everything else I described, the car is now running 50 degrees hotter. At first I was thinking I had a 160 or 180 thermostat and that after the shop flushed the system they replaced the thermostat with an OEM one - but I checked my shop receipt and there is no mention of a thermostat replacement (and I called the shop to verify). In addition, thermostat housing bolts don't look like they have been touched in years, so at this point I am thinking its still the original thermostat. Car only has 95,000 miles on it and is in otherwise excellent condition.

If the car is designed to run at 230, and recommends to turn car off at 260, there doesn't seem to be much room for error. I would imagine lots of vette owners are sitting on the side of the road on hot days waiting for their cars too cool down.

What can I do to get my car running back down around 180 again?
1) replace thermostat with 180 thermostat??
2) can I lower the factory .Pri fan to turn on at a lower temp?

I am going to try to bleed any air out of the system using the bleed screws...should car be hot or cold to do that?

Thanks

**Hib Halverson** · 10-07-11, 09:43 AM

If you are reading coolant temp from the analog gauges, know that they are inaccurate.

When the hose blew, if it happened while you were driving, how far did you drive after it failed and how hot did the engine get?

Have you had to add any significant amount of coolant?

To bleed the system, warm the engine to operating temperature then use a tiny wrench and open each bleeder until it "spits" coolant. Shut off the engine, allow it to cool, then check the coolant level.

I'd also pull the top of the cooling stack off and clear any debris from between the HVAC and the radiator then make sure the front air dam is functional.

And, verify both cooling fans are working properly using the diagnostic instructions in the Factory Service Manual.

A 180 thermostat and lower the fan ons can lower operating temperature somewhat, but the strategy here is to find out why the engine is running hotter than it did before.

**rolinger** · 10-07-11, 09:51 AM

Thanks guys.

Going to start looking into all this. Yeah, I agree, I don't like just fixing things without knowing exactly what caused the issue in the first place.

Will post results soon.

**strokin383-c4** · 10-07-11, 12:10 PM

Originally Posted by rolinger

Thanks guys.

Going to start looking into all this. Yeah, I agree, I don't like just fixing things without knowing exactly what caused the issue in the first place.

Will post results soon.

Also make sure your Thermostat is opening. Or just replace it with a nice HD balanced 180.

**rolinger** · 10-07-11, 01:17 PM

1. The analog gauge has always matched the digital read out. When digital read out was 180, so was analog gauge...now the digital is reading 235 and the analog guage is almost right at the warning stripes at the 260 mark

2. Was driving about 75mph on highway, hose blew...maybe I drove with it a minute before I saw it. Turned of engine immediately and coasted to side of road.

3. While engine completely cold, overflow tank looks right level. High Fill Reservoir is low, mixture about 2+ inches lower than filler neck. This would appear to be the air in the system ("add coolant" light). Have not yet added coolant.

4. ordered an HD 180 thermostat and a new lower hose...the upper blew last time, might as well replace the 20year old lower hose too.

5. No debris or blockage that I can see anywhere on the cooling stack.

Last: I have the 1992 Corvette Specifications manual (lists all the MVMA specifications) and the 84-96 Haynes Repair Manual. the MVMA specs say the t-stat opens to start cooling at 180, the Haynes says it opens 195. Either way...180 or 195, I don't see how Vetteoz comment "Exactly were it was supposed to run (230F) from the factory. Pri fan doesn't turn on until 228F" can be true.

Based on all my reading, the car should be running, on average, about 10 degrees hotter than t-stat opening temperature. Yes? No?

**2VettesMike** · 10-07-11, 03:06 PM

This may or not help you but here goes. Owned a 93 since 96. One water pump and t-stat at 125K as preventative maintenance when the optispark died.

In that time temp's are:

Interstate/in town moving 192-196F
Sitting in traffic AC on (fans on automatically) 194-196F
Sitting in traffic AC off, slow climb to 228F, one fan on, cools to 221F, cycles fan off.

On a rare hot day idle in the driveway I have tested and gotten the 237F second fan to come on.

178K miles and still going strong.

Thanks and good luck,

Mike

**rolinger** · 10-07-11, 03:14 PM

2VettesMike:

Thanks. Yeah, mine is running 235 at 70mph on the highway with the A/C (thus fans) running. Something is def wrong with my system. Just got the new thermostat, will be working on everything in about an hour.

**93Rubie** · 10-07-11, 07:14 PM

I am willing to bet that you have air in the system and that is your only problem. The procedure is in the Owners Manual, as well it can be found in the FSM. Field Service Manual. While replacing the t-stat and lower hose is a good idea. I think the real problem is you have air in the system, and nothing more.

**strokin383-c4** · 10-07-11, 08:53 PM

Originally Posted by rolinger

1. The analog gauge has always matched the digital read out. When digital read out was 180, so was analog gauge...now the digital is reading 235 and the analog guage is almost right at the warning stripes at the 260 mark

2. Was driving about 75mph on highway, hose blew...maybe I drove with it a minute before I saw it. Turned of engine immediately and coasted to side of road.

3. While engine completely cold, overflow tank looks right level. High Fill Reservoir is low, mixture about 2+ inches lower than filler neck. This would appear to be the air in the system ("add coolant" light). Have not yet added coolant.

4. ordered an HD 180 thermostat and a new lower hose...the upper blew last time, might as well replace the 20year old lower hose too.

5. No debris or blockage that I can see anywhere on the cooling stack.

Last: I have the 1992 Corvette Specifications manual (lists all the MVMA specifications) and the 84-96 Haynes Repair Manual. the MVMA specs say the t-stat opens to start cooling at 180, the Haynes says it opens 195. Either way...180 or 195, I don't see how Vetteoz comment "Exactly were it was supposed to run (230F) from the factory. Pri fan doesn't turn on until 228F" can be true.

Based on all my reading, the car should be running, on average, about 10 degrees hotter than t-stat opening temperature. Yes? No?

On an L-98 the thermostat opens at 180. Thus why the thermostat is labeled 180. in lamens terms. a 160 opens at 160 and a 180 opens at 180. my HD 180 opens at 180, and will drop down to 170.

**93Rubie** · 10-08-11, 08:04 PM

Originally Posted by vetteoz

As I stated in my 1st post.

The OP has stated he was not aware of the purpose of the bleed valves
( and their required use when refilling the system)

I also posted a link to the correct method of refilling a LT1

My bad, missed that, continue....

**rolinger** · 10-11-11, 12:13 PM

First off, thanks everyone for you help, explanations and suggestions. The issue appears to be fixed.

Number 1 issue, apparently when the hose blew the engine overheated so much that it damaged the thermostat. From that point on the thermostat struggle to work correctly gradually getting worse and worse. I bought and put in a new 180 tstat and the car temp (and analog gauge) are both reading at 190 now. It could be the original thermostat (from 1992), but I doubt it since I have had two full tune ups on the car and I imagine that the tstat would have been replaced at each tune up.

Number 2 issue, the "add coolant" light no longer comes on. I filled it to proper level, bled it out and topped it off again. Though this didn't help the system, the real culprit was the tstat.

Last question: could extreme overheating on the engine cause it lose power? Yesterday morning, before fixing the tstat/cooling issue, I had to drive the car. It reached 244 degrees on the highway, I pulled to side of road, shut off car and sat for 10 minutes. After turning on car and merging back onto highway, in regular "D"rive, the car virtually had no power until it reached about 30miles an hour - then I could feel the full power kick in. After exiting highway and going through surface streets for about 2miles to my home, the loss of power happened two more times taking off from stop lights.

Knock on wood, she is still 100% stock and going strong...and everyone who see's her thinks she just came off the assembly line. In the 19 years I have owned this car (95,000 miles) the only things to have gone wrong with it are:
1. blower fan module died
2. Antenna mast broke (and replaced)
3. side view mirror back-plate broke
4. upper radiator hose blew ultimately leading to this whole thread about the thermostat failing
5. I did replace all the weather stripping...original dried and cracked causing window leaks.

...driver side seat "grinds" when using the auto-seat controls (back movement only). Reading tells me a cable needs to be replaced. Will be working on this one soon.

**John Robinson** · 10-11-11, 09:31 PM

You might replace the radiator cap. If it is the original cap it has served its purpose. After the hose burst the spring in the cap may have gotten hot enough to not be able to hold pressure when hot and a vacuum when it cools off to pull fluid back into the engine and fill the air pockets from the overflow tank. When you replaced the t stat you had to remove the radiator cap and put it back on and in doing that you may have got it to seal again. And that is why now the engine is running cooler. Like you I have had the hose burst this year and then it would not pull from the storage tank to refill on cool down. I replaced the cap and it fixed the problem. Also if the cap is not holding pressure the boiling point for water (don't know for antifreeze) is 212 degrees When you have it under pressure it is much higher. On my LT1 it seems that the temp runs around 208 and in heavy traffic it goes to 235 with the aux fan kicking on at 228.