My 90 w/L98 overheats in town(stop and go)on the freeway,night or on cooler days it runs normal tempature.I replaced thermostat and had radiator flushed but neither has helped.Water was or is not rusty at all.Anyone with any ideas where to look next would be greatly appreciated.I have looked at front of radiator and there is nothing obstructing air flow.I've done the old trick of turning on the heater to release some heat and get the fans moving and this does help,but just slightly.I had a mechani tell me the fans are programmed to turn on from factory at 232 degress which seems awful high.I will order and install a kit that allows me to turn fan on without heater turned on but am sure this will not fix what the real issue is.I'd hate to wayste $ on a new waterpump if thats not the cause but looks like maybe the next step to take.Anyone else have this problem before? Please help.Thanks.

 

First, corvettes usually run at a higher opertaing temperature than other cars. Your mechanic was on track with the temps. You can also do some simple checks yourself to ensure the system is working properly. Check the belt, tnesioner, and hoses check to see if there is any debris blocking the flow of the radiator. Is the radiator clean (road grime) Spray on some simple gree on the radiator and hose off (don't get the engine wet). Also check for debris between the evaporator and radiator for debris as well.

 

Forgot to ask. After changing the thermostat, did you burp the system. If you didn't, this may be part or all of your problem. To burp the system (free it of air and ensure the system is completely full of coolant) park the car on level ground or at a slight incline uphill, remove the radiator cap (when the engine is cold) and start the car. Let it get up to operating temperature (thermostat open). Look into the radiator and watch the flow of coolant. Once it is flowing increase the rpm to 1500- 1700. If the coolant level drops, this may be your problem. Top the radiator off at 1500-1700 rpm and put the radiator cap back on before dropping the rpm.. This procedure may have to be more than once.

 

Forget about parking the car on an incline, it only works for up to 89, I just realized you have a 90.

 

What do you mean by "overheats"? What is your water and oil temp when it gets hot?

 

We need numbers. You may not have a problem at all.

 

http://temp.corvetteforum.net/c4/vad...erheating.html

 

Thanks for all the replies....Temp shoots up,according to my gauge to around 250 on the water...oil temp around 220..are these normal and safe temps?Gets a little scary to me seeing that high of numbers.As far as burping the system,ive done that.Thanks again .

 

250 is too high. Will it get that hot at idle? It sounds like time for a new radiator. I know you said you looked at the front and flushed it. Fushing can help but most of the deposit won't come out. To clean the front of the radiator you need to remove it. Pick the bugs off the front while it doesn't hurt really doesn't help much either. The dust and dirt that is the main problem will be between the fins. After the radiators out you can take it to the car wash and use the wand to spray it out. You are dealing with a 18 year old part and if it is weak this can damage it. A car that over heats slowly has a air flow problem. If it overheats quickly there are many different things that can be wrong

 

Coolant analog gauges on C4's are notoriously incorrect. Oil looks looks about right coolant temp is suspect.

 

Is there a known and expected relationship between oil and water temp?

EDIT: My bad, I see it in the previous post (http://temp.corvetteforum.net/c4/vad...erheating.html
).

 

Do the mod to lower the temperature as fast as you can. These cars overheated when they were new. When they get older they do not hold up to running on the edge of death.

 

http://gmtips.com/3rd-degree/dox/tips/cool/cool.htm

 

When my '90 started to overheat, it was the water pump taking a dump. I replaced w/ an Edelbrock High Flow, new hoses and thermostat,and it now runs at 195 to 210 in traffic.

BTW, I used a 195 degree stat. My fans come on at 200 degrees.

 

ok a little background info, last summer my 1986 corvette would run a cool 90 degrees celcius on the highway, now after taking it out of storage this spring i noticed it running much hotter on the highway than last year, it now runs between 105 and 110 celcius, im completely baffled as to why, the cooling fan comes on at around 105 degrees, but it does not shut off because the engine will not get cooler than 105 even with the fan running and driving at high speed, thought maybe it was my thermostat but the thermostat is opening since the upper rad hose is hot, the hoses are not collapsing, thought maybe the radiator was plugged so i flushed the rad today and blew out the fins with an air hose to clean it out and still no difference, could it be one of the coolant temp sensors? if its the one under the throttle body that controls the cooling fan, then why would the one feeding the temperature gauge read so hot? although if the one feeding temp gauge is at fault, then why would the cooling fan come on, but not shut off??? help im completely baffled and out of ideas.......

 

I don't know if this would be a good test or not, with the radiator cap off and bringing it up to temp put a meat thermometer in the coolant and compare it to the dash readings. I would assume fresh out of the block it should be close to the same values.

Just a thought.

 

Sorry guys, but I'm just not brave enough to see 232 on my gauge as "normal" for the fan to kick in.

If the fan fails, ..your going to very, very, quickly exceed 250, see a red warning on the readout, defeat the radiator cap and boil the expansion tank, as happened to mine driving down the road blowing off glycol like a WW2 aircraft with a radiator hit. Not good with ally heads, and I don't care what GM says, its unnecessary to be that hot and we do have days here in the summer when the tarmac melts.

I have removed the AC intercooler, fitted a 160deg thermostat, new hoses, back flushed the block and rad, dumped the stock fan relay and fitted an aftermarket controller that turns on the fan at 170deg. I also have a radiator cap with a lever assist to burp the system if needed.

Normal running for me is around 175 deg maxing out at 185 in traffic or on 80mph+ motorway runs for several hours at a time. My oil (Mobil 1 fully synth 10w60 track/extended life oil) runs a little hotter around 190deg with the pressure never falling below 65psi on a motor with 150k miles.

btw, I change my coolant every year after adding a bottle of flushing agent. I use a hosepipe on each component like the heater matrix, rad, and block. You should see the crud that comes out!

 

On my '91 ZR-1, I put in a duel capacity radiator, and a lower t-stat. You can also add the Water Wetter product to the coolant to help. Turning on the AC will also cause the fans to turn on, this will help in stop and go traffic. I just bought an '89, and plan on doing the same for it. I also noticed when I replaced the water pump on my '92 L98 trans am, that it dropped the temp about 10 to 15 deg.

 

the coolant temp is NOT the same everywhere in the engine, and the radiator drops it about 20*.

The statement that these cars overheat when new is balderdash. They run hotter than any of us were used to or comfortable with, but mine never overheated in a hot climate until I modified the engine.

I did install a lower 'trigger' thermal switch on the stock motor, primarily for my comfort with fan ON temp.

If the car overheats there is insuffient coolant or airflow. If only on the highway, it is often due to leaves and crap, which has been discussed ad nauseum here. Low speed overheating only, points to fan problems.

Lower value thermostats might give the system a running start, offering a larger passage sooner, as coolant heats, but as a constantly changing valve, can only open so much. I found Robert Shaw stats allow more flow due to larger oriface; 180* is fine.

I am unconvinced that high flow pumps cool any better than a non-failing stocker, based upon my experience and discussion with cooling engineers. Coolant needs time to absorb and dissipate the heat, and must remain in either area long enough for the heat transfer.

After my car sat for too long, a while back, I saw corrosion coating the internals of this aluminum radiator. I found and used an obscure MB process of running a weak (10%, I think) acid solution for a short time to remove it. By short, I mean startup to normal op temp.. ONLY. there was no rule found, for the cutoff between its effectiveness and erosion of the good portions of the heads and radiator. The acid wash process helped immensely.

The basic and simple things; do 'em first!

 

If you still run your egr system on the car and your emission equipment; running the car at 170 to 185 degrees will have long term effects. THis is why the cars ran hotter. They have to burn up soot/carbon created by Egr. If you want to to run cooler, get 195 or 200 degree thermostats. If you have removed or deleted the Egr , then do what you want.