I know this has been discussed ad nauseum, but I haven't been able to find a thread that mirrors my exact issues, so my apologies for starting yet another overheating thread. This car has had an overheating problem ever since the engine was rebuilt by the previous owner, but since it wasn't a daily driver and was only driven in cooler weather, it was never addressed. I'm going to use a numbered list for ease of responding. Thanks in advance for any and all help and advice!

1. Car is an '89 coupe with auxiliary fan that comes on around 235*.

2. 350 has been rebuilt and now runs about 11.25:1 compression (based on calculations) using flat-top pistons with close-to-factory spec cam. Other than that the engine/air inlet system is stock.

3. ECM has been tuned to provide more fuel (a lot more) to combat lean issues, but it still has pre-detonation issues at part throttle or when hot (over 190*).

4. Stock ignition module. Accel "hot" module didn't seem to help.

5. Stock exhaust manifolds, aftermarket cat-back.

6. New aftermarket aluminum 2-core radiator.

7. New radiator cap.

8. Clean space between radiator and condenser.

9. Intact air dam.

10. Water pump was replaced with aftermarket unit when engine was rebuilt. Someone told me that only factory AC-Delco water pumps worked "properly" on L98s.

11. 160* thermostat, functioning properly.

12. Main fan has been programmed to come on at 180* and turn off at 175* when A/C is not on. Works flawlessly.

13. Alternator maintains 13.6-13.8V at speed with A/C on.

14. Water temp and oil temp always remain relative to one another.

15. A/C charge has been checked and found to be at the proper level.

16. Air temp out of the vent is only about 55-60*.

On an 85* day, when driving without the A/C on, the system cools just fine. With the A/C on and at highway speeds, it'll maintain about 185-210*, depending on speed and air temp. Around town in stop and go traffic, it'll run anywhere from 210-235*. Even worse is when I've been on the highway and then get back onto city streets. At that point, it seldom cools below 220*, and will climb to 245* (or until I turn off the A/C, whichever comes first), whether I'm sitting still or going 40mph. When air temps get above 90* or so, I don't even bother to drive it any more. What am I missing here?

 

My first question is how do you KNOW your car is running 245 at times? Are you shooting your engine with a thermo heat gun or do you have a gauge that is accurate? If you are relying on your car gauges they can be way off.

My initial thought is that your set up seem to be pretty squared away. My first guess is that you need to have both main and auxiliary fans working earlier in your cycle.

Running at 225 (while not optimal) is totally in specs as your auxiliary fan comes on at 235. That is what I'd be focusing on; Just wire the auxiliary into the main so they come on simultaneously at the 180.

Also, you are running 11.5 (!!!) compression so your engine will run hotter. Sorry, you are expecting your cooling system to work at factory specs with a non factory spec engine.

I bet if your get that aux fan to come on earlier you will be good.

 

You're right Bill, I don't know how accurate the factory gauge is, and yes I expect it to run a little hotter with that compression. I'm just surprised that the system can't keep up with the minimal "upgrades".

 

Also, check you timing and advance as far as you can (comfortably) go. You will get a performance boost and your engine will run cooler.

 

I've got as much initial cranked in as I can without the pre-detonation getting silly. I believe it's at 10.

 

Is that what the chip guy said to do? If he assumes 6 and you put 10 and run that high a compression, it might have issues. How did they write the tune? Did they dyno or do a SWAG based on what you tell them?

 

I honestly can't answer that, as the tune was done while the previous owner owned it, and I'm just going off of what he said. I can tell you that I've played with the timing a bit and have found the car runs it's best overall with where I currently have it, but I honestly don't recall if I have it set at 10, 14, 2, etc.

 

Problem is the program might assume you have a certain base timing and go from there. Mine was set to 0 but the ECM doesn't care, as I understand it. It will advance based on what it was told to do. So if I jacked it up 10 degrees and the ECM advances it 20, I would have a total of 30 degrees. After which, it will run well at some points and detonate at others. Will you know? Doubtful since any sign of detonation and the ECM will pull timing unless it is grossly out of the ECM ability. This is why I think that you need to get it tuned properly on a dyno so that it can be maximized throughout the curve.

 

I'd also confirm proper heat transfer capability of the radiator. Mine (aluminum) had some internal corrosion, which decreased thermal transfer. The car's cooling well while moving, but not while stopped, tells us that airflow is the probably issue hence Bill's comment about fans.

I've battled this dragon a few times, with my modded engine and learned that stock rad and WP can handle power up the the 700 range. (I wish I knew that before throwing aftermarket BeCool and more, at it!)

The thing that finally solved my car's problem was a Robt. Shaw thermostat, which flowed better than the Stant.

 

I kind of have questions about this. Idling in stop and go, mostly stop traffic in hot and humidity summer with the AC on max, I'm not sure if it can

 

With flat tops how are you coming up with that much compression>

What size cc do your heads have? Head gasket thickness, how far down in the hole are your pistons.

Doubt compression is your problem.
Which cam?

Get that fan turning on earlier 23x is too damn hot no reason for it
You can pass smog running way cooler

 

I have said this before, my 1986 vette when it was all stock had this same problem. If I turned the air on and let the car sit in my driveway on a 90 degree day the car would overheat (get too 245 degrees or higher, fan on), just like you are describing. The stock cooling system even with the aux fan could not cool the stock car when it was not moving or moving slowly with the air on. I think the stock cooling system is inadequate for these cars. I always had to turn the air off on hot days driving through town, on the highway it was OK. I fixed the problem with a Dewitt radiator.

 

Good point about the ECM and it's ability. I've often wondered why it didn't pull enough timing out to prevent pinging. I was planning on a dump tune once I got the cooling figured out, but now I'm thinking I should reverse the order!

 

I would hope the radiator has no such issues since it's new, but I guess you never know...

 

Heads have 58cc chambers, gasket is "thin" (according to previous owner), don't know the piston location but I assume it's .025" down (prev owner never said anything about a decked block), the cam is a custom grind with near-stock lift but more duration. No smog test to worry about here either!

 

Actually, it would sit and idle on a hot day and be fine AS LONG AS I hadn't gotten on the highway or driven in stop and go traffic. It's after it's gotten thoroughly warmed up that it has problems getting cooled down.

 

Thanks for all the input everyone!

 

That happened to me in my (built) 4th gen camaro. Hot day, A/C on overheat. Found that the condenser was clogged up with grass clippings(?)
New condenser and cleaned out the radiator (outside), fresh air dam and it never happened again.

 

Normally I would say that you do not have enough cooling fan but:

If checked properly AC register temps should be in the 40's which leads me to think that you may have a clogging orifice valve = to much AC high side head pressure = to much condenser heat.

Suggest checking AC high side pressure to verify if over 180# change the orifice valve.

 

Thanks!