I noticed my coolant temps have been rising lately, so I flushed and filled with new coolant (green stuff). No change in temps, though . I have historically run 194* on the highway in 6th gear and never got above 205* with AC on in traffic, but now I am running 205* on the highway and just today the auxillary fan kicked in for the first time ever when temps climbed to 223* with the AC on in traffic . I am getting scared to drive the car in traffic now, waiting for the car to overheat. Any thoughts on causes or remedies?

 

Just a guess, look make sure there aren't any plastic bags or anythng else in the front of the radiator.
The C4 Corvette is a perfect road vacuum cleaner, gathering everything on the road.

When I run over a piece of paper or especially a large bag, I always look in the mirror to make sure I see it exiting from the back of the car before I relax.
I've, more than once, had to stop and pull a large bag from up under the front air intake.

Tom Piper

 

Pull the surge tank cap, start the car and let it run until the thermostat opens, while reving the egine (around 2000 rpms), pour in some coolant and replace the the surge tank cap. This will purge any air out of the coolant system.

 

First things first: You did bleed the air out of the system after your flush/fill didn't you? There should be two bleed screws...

Tom Piper gave you good advice -- check for the presence of anything blocking airflow through the condenser and/or radiator. You can get a very limited view of the space between the condenser and radiator through a hole in one side (I can't remember which side).

What did the coolant that you drained out look like? It's possible that you've developed some amount of buildup on the inside of the radiator and/or engine block, but if the coolant that came out looked pretty decent, discard this thought.

It's possible that your thermostat is not opening all the way now. Consider swapping it out (and going with a 160*F replacement).

If you do go with a 160* 'stat, consider also having your ECM re-flashed to kick the cooling fans on at lower temp settings (but don't expect lower fan-on temps to solve the problem you're presently having, as I don't think it will -- it sounds like something's gone deficient in your cooling system).

I'm a bit puzzled about the behavior of your cooling fans. They should both come on with the A/C.

Good luck.

Be well,

SJW

 

i would love to be at 223 in traffic... in my opinion, i don't think that is high. i have always regularly been in that range and a bit higher with no problems whatsoever.

 

Ive said it before the water wetter will help out alot. Try it you wont be dissappointed .

 

 

I took a piece of screen.. (course, not the fine screen in your house window) the type with about 1/8" squares.. I cut it to fit below the front of my car (under the radiator) I did this because I have a Breathless bottom breather intake, & this prevents leaves ..etc from getting up there.. It also keeps the 2" space between the radiator & AC condenser clear of debris..

I also have a 160 thermostat, & Hypertech program to run the fans sooner..on a HOT day 90 deg with AC off my car runs 180-185 ... with AC on 190-200 tops..

 

On my 94 only the one (left) kicks on when the A/C is running. The other doesn't come on until it gets really hot.

 

Are you sure the green coolant is correct???
When did the C4 switch to orange?

Larry
code5coupe

 

I have a late 94, and it came with green coolaid.

 

Exactly what mine does.

 

Mine is a late '94 (#18399 to be exact ) as well and came with green stuff. They switched in '95 or '96.

 

I bled the coolant when the temp was 200* and higher to clear the air. The coolant that I drained was horrible -- completely saturated with rust. I am thinking that is the main cause of the increased temps -- too much sludge build up in the coolant passages and radiator. If I was going to keep the car, I would really dig into it, but I plan on selling it by year end, so I will not undertake a big project.

I have used Water Wetter in the past with mixed results, but I will probably buy another bottle this time -- couldn't hurt.

I'll check the area between the radiator and condensor, too. Thanks for all the suggestions .

 

Any car not running at or close to the stock thermostat at cruise isn't right. Assuming you didn't coincidently suck up a shopping bag, your cruddy looking coolant is the key. Draining it probably clogged up some of the passageways with what was being held in suspension. You can try to flush it or have it hot tanked at a radiator shop, or simply replace it. Don't be surprised if your heater core gets plugged up next - in fact did you try the heater?

 

I would flush it a few more times and get all the crap out of it, then refill with the GREEN..

 

No stock LT1 I know of runs anywhere near 180*, the stock thermostat rating, so I am not sure about that comment. I did in fact flush the coolant several times until the water ran near-clear out the radiator drain, so I think I got most of the crud out that could come out. Some of the crud is probably still stuck in there, though. No, I did not try the heater yet -- I will tonight. Thanks

 

Hard to imagine it left the factory running much higher than the thermostat at cruise - GM put the 180 degree thermostat in there for a reason - is the design flawed???? I would think that with reverse cooling, the sender in the head, you would see something close to the 180 at cruise - but maybe not - coolant temps are as much a function of capacity as they are of the thermostat. I do know that every car I've hooked up a scanner to has always been close and that gages can be inaccurate or with the sender in the head, usually a couple of degrees warmer then the CTS signal. Hopefully, a good flush will get you back to where it was - don't think it needs any magic elixirs or a different thermostat until you accomplish that - it certainly didn't when it was built.

 

I have a 160* t-stat in my stock '94 six-speed. I also had the ECM re-flashed to kick the fans on/off at lower temps (190/180 primary, 195/185 secondary, if I recall correctly). Cruising on the open highway with the A/C off on a mild day, it runs ECTs between 171* and 174*. On a really hot day, it cruises more in the 180-something-degree range with the A/C off. With the A/C on, in stop & go traffic on a hot day, it'll sometimes creep up to around 205*.

All of these temps are WAY lower than I routinely saw before making the changes to the 'stat and fan settings. Stock settings for fan-on are 228* primary, 324* secondary, so at idle, even on a cool day, it would hover in the 220s.

Be well,

SJW

 

Next time, make sure the heater is on when you flush. When I flush mine, I like to remove the lower radiator hose at the radiator. This will allow the larger chunks that won't pass through the petcock to escape. Besides in my car, it saves going underneath. If you think "Some of the crud is probably still stuck in there", it may pay to try it.

RACE ON!!!