Howdy guys! New corvette owner with a new vette. It's either bad luck or a well hidden problem, but I have a 94 Vette that just started overheating today on my way home. Stopped at a drive thru and noticed the temperature had climbed up to the 2nd notch past 180 (I think thats around 235), so I got out and on the road ASAP thinking that maybe it was just a lack of airflow, and on my way out the lot it died on me. Thankfully she started up again, and I got her home with the temp at 210 most of the way. It started rising pretty fast when I got in the neighborhood, and was at about 220 when I turned her off. It sounds like either a closed thermostat or a burned fan clutch to me, but I'm not certain. Anyone have any ideas on other things it would be, or know how to check the fan clutch or thermostat?

 

lol

The LT1 runs pretty hot. Not laughing at you but laughing at how I thought the same thing. The second time I drove the car the dash electronics showed around 230 and I got off the fwy right away panicking but its normal.

Speeds above 40-45 mph you should be at 195-205. It might take a few mins to bring it that low if its hot outside. If youre going slower it wont get that low but will stay below 210/215 from my experience. If youre going real slow it will keep climbing to 228-235. Around there the fans should start up and bring the temp down to I think 205-210?

Some ppl like to keep the AC running to have that fan going even if the temp is below 230. Others do the t stat replacement but its not needed from what I've read. Maybe if you're doing bumper to bumper commuting in the desert aka socal

Coolant flush is always a good idea on a new-to-you car though! Welcome to the forum.

 

Ok. Had the AC running while it was stationary but it didn't seem to help, makes me suspect the fan. Kept it at 50-60 going home, but would nearly die when at a red light for more than about 45 seconds. If this is a head gasket then I quit lol. Coolant light never came on and coolant is at a good temp. Heading to Autozone to get a Haynes manual on the thing and some coolant, and prolly some rags to cover the opti. Never done a flush before, so any recommendations on things to do or not to do, or any thoughts on what else it might be?

 

Take to a shop. C4's are not as easy to flush as some cars. If you have never done one this is not the one to learn on. Dan

 

Have you had a chance to check out the radiator and air flow? If you have debris in the radiator and condenser crevices, you can get a rise in temperature quickly.

Our cars are like vacuum cleaners--- if you ran over a plastic grocery bag and sucked in up into the radiator the blockage can cause you to over heat very quickly.

 

Over-heating is caused by lack of coolant flow, or lack of air flow. Block one, or both, and the vette will over-heat.

1. Is there sufficient coolant in the system?
2. Have you checked for debris in front of the radiator?
3. Have you check the air dam for damage blocking air flow?

The fans are of no concern at speed, only at low speed or idle.

You may have more than a temp problem (if you have a temp problem (?)) if the vette dies.

You should always confirm temp using the digital gage, not the analog dash needle.

You can test the t-stat by removing it, and placing it in boiling water to see if functions (opens).

If interested, answer the 3 questions above, and we will continue.

 

Coolant level is where it's supposed to be
Nothing in the front of the radiator blocking airflow
Does not appear to be any damage to the air dam, anyone know the clearance needed there for optimal airflow to be certain? Otherwise air dam does not appear to be damaged in a way that would block flow. Lemme get a picture

 

Apologies for the poor light quality, nighttime here and used my phone light

 

Your front condenser looks clean but there is a space behind the condenser and the radiator,,,,,THAT is where the crap gets stuck.

 

Ok. Do I need to remove the air dam to check that out? It's probably really obvious to check but I don't see it...

 

No need for a dam photo.

I'm assuming "coolant level is where it is supposed to be" to mean the system is full, including the overflow bottle at the proper level.

You are working with a closed coolant system, meaning no outside air is allowed to enter the system. When hot, the coolant expands into the overflow bottle, and during cool-down, the coolant siphons back into the reservoir. A closed system allows for pressure to build increasing the boiling point of the coolant. Pressure is controlled by the rad cap at about 15#.

If air enters the cooling system via split hose ends, damaged rad cap gasket, loose hose connections, etc. then the boiling point increase is negated, along with the return siphon during cool-down.

If the t-stat is ok, then think about a coolant flush.
A proper flush includes removing the 2 knock sensors located in the bottom of the block. Just allowing coolant to flow out the sensor holes is not sufficient to remove the 20+ year sediment. You need to squirt water under pressure in to sensor holes several times..... nasty/smelly job

Replace knock sensors with new..... sensors come with thread sealant applied.

I'm betting on a faulty t-stat.

If buying a new t-stat, ensure that it is for the LT1 engine. A special t-stat is required.

 

Awesome! Are there any special tools I need to do the flush, or to replace the thermostat? I've got some power tools, a big craftsman wrench and socket set, and whatever odds and ends I can get at AutoZone

 

Test the t-stat before continuing. Flush can follow at any time.

No special tool required for removing the t-stat. Just take care not to cross-thread unit. Even if the t-stat checks out to be functioning properly, I would replace with new.

 

The nice thing about a LT1 Thermostat is, it doesn't require any gaskets or scraping off old sealant. The T-stat comes with an 'O'-ring already installed in it. Just take the housing neck off, pull out the old T-stat and drop in the new one. No mess like other old engines. One of the easiest jobs to do on an LT-1.
Just make sure the parts guy gives you a T-stat for a LT-1, because they are different from others.

 

There is no fan clutch.

Did your fans come on at all with the a/c on ? or without the a/c ?

I think you will also need to find out why your car is dying.

 

You may have to remove the fan shroud. Looks harder than it is. You are "In and out" in about an hour.

But first, take a flashlight and look between the cracks in the shroud to see between the condenser and radiator. It you don't see anything then you are good.

I've seen the front condensors clean as a whistle, and then the "in between" space almost half full with leaves, plastic bags, housing insulation, cigarette butts and a larger slurpee paper cup. Once cleaned out the car cooled nicely.

 

I just scored this yesterday for $16...I see it when up in price, but still a good deal

 

Ignore the analog coolant tem gauge! The analog gauges are not linear so that "2 notches above 180" really doesn't provide any accurate/useable information. Keep the digital display showing "COOL F". That will display a much more accurate coolant temp value.

And as mentioned, C4's do have higher coolant temps compared to other cars. In fact, the secondary cooling fan does not even turn on until about 238 degrees. The fan also comes on when the A/C is running so that's a good way to check if that fan even works.

If you do decide to replace the 'stat, make sure that coolant does not drain down over the OptiSpark!! It doesn't like liquid and it will die if it gets soaked. Hundreds of dollars to replace If you can't get the car off the ground to where you can easily slide under, consider having a shop do the flush/fill. Most good shops have equipment that will remove all of the old coolant and add fresh coolant.

The '94 uses green (ethylene glycol) coolant in a 50/50 mix and it's a good idea to replace it every 2-3 years. If the radiator hoses are original/old, it would be a good idea to replace them when you do a flush.

When the engine died, did the SES light stay on after re-starting? Check for any error codes; AutoZone can do this for you if a store has an OBD1 scan tool.

 

I am surprised no one has brought this up(maybe someone did and I did not see it). The c4 lt1 engine has a bad habit of developing air pockets. It does not do this on its own. If you make a big mistake and open the cap on the overflow fill while the engine is hot, you relieve the pressure and allow the coolant to boil forming air pockets. I know because I was scolded about this when I was looking at the cars. GM knows about this and so should every lt1 owner. GM put in bleeder valves to fix this, so look it up and make sure you cover the opti because it can be a messy job. Turn on your a/c to see if the fan(s) start up. They should. GM has over complicated the parameters for the fans to start with many switches including high side a/c pressure. Blah. The lt1 is not for the faint of heart while driving in heavy traffic on hot days.

 

Should be able to see it from the side looking between the ac condenser and radiator. My 94 had a huge matt of dirt and grass covering about a 3rd of the radiator.