I know there's a lot of us out there that has a 90 model year L98 C4. I am helping a friend out with one and he has what appears to be an engine cooling issue. I ran a datalogging session with his car today, and on the freeway the engine coolant temperature is running between 105.5 and 113 Deg C or 221 and 235 Deg F. Mind you this is traveling down the freeway at normal cruise speeds on a 70 degree ambient temperature day at near sea level.

He says there is a new radiator, a 165 Deg thermostat and I checked the air dam under the car and its intact, and there is nothing in the front of the radiator that is blocking air flow. I was told by a a couple GM techs that these do run hot, but I don't remember them running this hot. At Idle sitting in the shop it run up to 108.5 or 227 Deg F. Both fans were running as well as they should have been as commanded by the ECM to come on at 108 and 113 Deg C.

My car will run at 85 Deg C or 185 Deg F all day long cruising or at idle it may pop up to 89 until the cooling fans are commanded to come on. However my car is a 95 LT1/4 series engine. However the radiator system is very similar. But other than that cooling systems similarities end with the LT1 reverse cooling system.

Anyone got any ideas as to why this thing is running so hot. I had thought perhaps he had the wrong water pump installed, one for a v-belt car vs a serpentine belt unit. But he swears it's the right pump, and besides I would think it would overheat severely with the wrong pump installed.

 

Your friend probably has air in the system. C4's are infamous for that.

This is usually prevalent in older C4's as the front spring sags causing the top of the radiator to be lower than the engine. This makes an for air bubble whenever you get into the cooling system.

There are several ways to cure this. I run without a thermo. This keeps that airbubble from forming. But in other states than CA, you might not want to do this.

The easiest way and the way I did it before my engine rebuild was, take off the radiator cap or at least to the first stop when the engine is cold. Jack up the car from the front jack points until one or the other front tire is off the ground. You can jack from either side. Start the car and let it warm up to normal orperating temp or beyond the temp your thermo opens.

Shut the car off and let it sit 3-4 hrs or overnight preferably. At that angle and when everything cools and contracts, the airbubble will work itself out. In the morning before starting, lower the car, top off the rad and you're done.

You can also drill one or two 1/16" holes in your thermo (in the part that doesn't move). This also allows air to bleed through and you won't have to do this again. Mustangs had a big problem with this awhile ago.

Good Luck,

BIG JIM

 

I would say he has air in the system too, either that or a Water Pump. Are you sure his stat is even opening? The temp gauge should pause for a couple minutes when it opens.

Remove the radiator cap and make sure the engine is allowed to get past the stat temp, refill with water and keep doing it for a few minutes so that all the air gets out.

If that doesnt fix it, his WP is likely shot.

 

I had a slight leak in the intake manifold on my 90. Not enough to leak any fluid, but it kept my cooling system from holding pressure, and subsequently it would run hot, especially in traffic.

Mark

 

I had a similiar problem, AFTER flushing my entire system!! So, after being told, by a few people here on the forum, how important it is to 'burp' the system, I did it, and have yet to see over 205 again, even sitting still on an 80+ day. (it's the highest it's hit around here so far this year!!)

 

How I fixed it: I installed the temp sensor probe in the side of the motor that Ecklers sells. It makes the fan kick on sooner. You can by a switch that they sell as well that allows you to turn this sensor off and let it heat up to what it use to. That might be benefitial in the winter time. :thumbs:

What my problem was:
On my 1991 C4, L98 engine I was having an issue with the engine getting so warm, 205-235 degrees that I installed the new sensor.

I have the stock setup, at 225 degrees kicks fan #1 on, so it works like it's suppose to. I did learn that the fan on the dash is a tab it off, so it's about useless. After reading the other problems of ppl finding out these things run warm, when sitting still.


[Modified by tgroghan, 7:03 PM 5/23/2003]