Happy Friday to All,

As you may know I bought my first C4 about a month ago, my other 'vettes are '75 and older. It did not run when I bought it, needed a new opti-spark mainly, it had not run for about 10 years. I replaced the opti-spark, fuel injectors, fuel pump, water pump (with a stock water pump), fuel filter and got it running nicely. I drained as much coolant as I could without pulling the knock sensors, then filled it with distilled water and ran it for a few days, then drained that (again without removing the knock sensors) to get a 50-50 blend and have been driving it since. I also used the 1" PVC with an elbow on the end to vacuum the front of the radiator, which pulled out some stuff but in general it seemed pretty clean.

It runs warmer than I think it should. When I take a kid to soccer practice I have to go uphill on back roads for about 4-5 miles normally doing 0-30 miles an hour or so, the car will get close to 230°F on an 80°F afternoon, which seems warm to me. When I go down the backside of the mountain it will cool down to about 205 when I go a bit faster on straight roads kind of coasting.

On the highway at about 70 on a 75°F day it seems to stabilize at about 205-210°F which I think is reasonable. When I get off the highway and take the last 2 miles to the house it will climb up closer to 220°F and when I park it I can hear it gurgling a bit into the overflow.

I have 'burped' the system pretty well I think. When I first ran it the low coolant light was on for the first few times I ran it but that has not come back on.

(note that I am looking at the digital readout, which seems to match pretty closely the analog gauge, for example with the digital is at 230°F, the analog gauge is at about 3/4.)

So me questions are, is this hotter than it should be, and if so, where should I look to bring it down a bit?

Thanks,

Scott

 

What year is the car? I want to know that to see when the factory fans are programmed to come on. Irrelevant to that, have you checked to make sure the radiator is clean both inside and out, the air dam is in place and the fans are operational? If the answers to that are yes you could have the fans programmed to turn on earlier to keep the car from climbing up to 230 degrees. The factory LT1's have 180 degree thermostats and having the fans turn on at 205 and off at 195 will not hurt anything and can give you piece of mind.

I just noticed in the title to the post that the year is 1992.

-The 1st fan for your car is programmed to come on at 226 degrees
-The second fan is programmed to come on at 235 degrees

It appears if you want cooler temps you will have to have the chip reprogrammed to turn the fan on earlier.

 

I am thinking that if you are hearing gurgling at the overflow tank you may need to add some coolant. The coolant surge tanks are designed to accommodate the expansion of the coolant without sucking air. If it is sucking air, you are low on coolant.

 

I replaced the thermostat with what is supposed to be the OEM equivalent that I got from NAPA when I replaced the water pump. I have verified that the fans come on, normally it seems they come on at about 220. I have not removed the radiator or flushed it other than running the distilled water through the system for a few days and then draining it. The air dam is in place. The car only has 75k miles on it and the previous owners kept it very stock so I don't think they reprogrammed anything.

 

I checked the coolant level religiously for the first several times I drove it after I filled it with coolant. The surge tank is always full after it cools down, and the overflow tank fluctuates between the hot and cold levels as I would expect. So I don't think it is low. I have opened the bleeder on the thermostat housing and it never has air.

 

Did you verify that the new thermostat is opening completely before you installed it? I've had that happen to me before. It will flow some coolant but not enough to properly cool the engine.

 

Everything sounds normal for the stock temps. Not sure when they changed but the later models had two stage fans worked at the same temps. I had my 91 reprogrammed to both on at 205 off at 200.

 

Just a couple of thoughts


First, Not sure running water a few days is going to clean the built up crud from the radiator after sitting 10 years. betting it is at least partially clogged. Maybe shoot ain IR heat gun at several spots.


Second, are you saying after the fans turn on at 220 the temp keeps rising to 230?


I've only seen above 230 once on my 92 and that was sitting waiting on a train with the A/C off. And as soon as the fans kicked on there was noticeable drop in temp.


With the A/C on both fans should be running all the time.

 

When you replaced the WP, did you also replace the radiator hoses? If they are original to the car, it may be that the lower hose is collapsing which cuts down on the coolant flow.

Also, there is a second bleed valve on the driver's side of the throttle body. Did you open that one too when you bled the system?

 

I did replace the radiator hoses. I don't think the 1992 has the second bleed valve.

 

The A/C is not charged so I have not been turning it on, that is on the plan for next spring. Yes, the temp will creep up to 230 with the fans on.

So it sounds like my next step should be to clean out the radiator inside and out. Would you agree? Is there a recommended procedure for that?

 

IF it where me, I'd buy a new radiator. I currently have my cooling system removed. I had a pinhole leak in the upper radiator hose at the engine. Since pretty much the entire system is 25 years old I couldn't see keeping any of it. Since I only drive around (no racing, tracking or autocross) I went with a service grade replacement. They're less than $150.


Of course wiser people than I suggested that while in that far I should check the Optispark. Once the hoses and water pump are off, your 3 balancer bolts from accessing the Opti. It was trashed. bearing sounded like gravel and it was full of rust.


If It were just the cooling system, i could pretty much do hoses, radiator and pump (using Gates Brand) for around $300. But add a new Optispark, oh and the balancer had missing rubber, and the thermostat housing had deteriorated at the hose mounting surface. Did I mention I need a new temp switch in the water pump.


I was told I'd be into this for a grand before I was done and I'm really close to that now.

 

My 96 was running the same temps as yours. I flushed completely (with new knock sensors) and installed a new 180deg thermostat from Ecklers. I now run 193 at 75 mph even on a 95 degree day. I will go to 208 in stop and go traffic. I also replaced hoses. Dan

 

Yes it does. It is located on the IAC housing, under the TB.

 

LT1/LT4 cars hitting 230 in traffic is PERFECTLY NORMAL with the factory programming !!!! The PCM turns on the fans, and it doesn't kick the 2nd fan on until about 230 deg F.

If you are out on a hot day - and the car is not moving very fast - you can expect to see the 230 mark. Steady state freeway cruising - the car should stay under 200 F. It normally doesn't take much more than a few miles of 40+ MPH to get the coolant down from the 225 mark back to around 200F.

If you find this unacceptable - you have several options. 1) Get the PCM reprogrammed with lower Fan 1 on and Fan 2 on temps. 2)Wire in a manual switch to turn both fan relays "on" whenever desired.

One final point - seriously consider pulling the knock sensors out - when I pulled them out on a "new to me" '92 LT1 car - the amount of crud that came out was pretty darn impressive!!! It's a messy job - and you're all but guaranteed to have coolant in your hair and running down your arm - but with the LT1 reverse cooling systems - the block seems to be where a lot of the crud ends up - the only way I feel fairly confident of getting it out is to open up the block drains - then to flush some water through the system till it all comes out clear for a little while. And while you're covered in old coolant - a heater core "flush" isn't a bad idea either....

 

Update:

I drained the coolant and hooked up a flush kit and gave it a good flush and it seems to have helped quite a bit. What came out did not look bad, but there must have been some stuff stuck in there clogging the flow. I spliced the heater hose and put the garden hose attachment in there and flushed it before I started it up, then turned off the flow and let it get up to about 200°F and then flushed it some more then took it for a drive. It did not get about about 205 in the slow areas and cooled down to about 195°F on the highway at 65 (bear in mind it is about 60°F this evening). I will plan on taking out the knock sensors and giving it one more flush before draining and refilling everything but hopefully this will resolve the issue.

 

Further update:

I added some of the Prestone flush stuff and have been driving it for about 2 hours and the temperatures are a lot better, from what I have read they are close to normal. I will drain it this week and put in antifreeze and hopefully not have to worry about it for a few years.

 

Thanks - You are correct, I just went out and looked at it. Not sure where I was told it only had one.

 

You have to remove the knock sensors to flush all crap in bottom of block coolant passages and remove radiator to correctly clean the fins with reverse water and then air pressure and then have access to blow out AC condenser, this is the best way to achieve max radiator efficiencey and is worth the labor, you will be very happy and surprized at the crap in there. Sorry about the spelling

 

Your Temps are well within reason.. once the A/C is up and going you'll see a reduction in temps around town..