Overheating Mystery

[393LX]

I’ve got a very mildly worked 89 GT with AOD. Car is running a Vortec supercharger making 350 to the wheels. Couldn’t stand getting beat by Camry’s

So, here’s the problem and why the car has been in the shop for months. My mechanic is at his wits end and is running out of things to try/replace. Car runs perfectly but after a while starts to overheat. So, in an effort to fix this, we have done the following - external trans cooler so radiator doesn’t have that job, custom ducting so all air goes through radiator, custom Griffin radiator with Spaal electric fan. We have tried 4 different brand water pumps and every temp range thermostat. The engine has been flushed multiple times.

Here is our best case at present- with a 195 thermostat, it seems to hold temp. Until... we put it through 2 run cycles, shutting if off in between. At the beginning of the 3rd cycle, it starts normally and then within a minute the temp gauge flashes like you threw a switch and the radiator cap starts to boil over. We are at at total loss what to do from here and are begging for any help with ideas we haven’t already thought of.

Some final thoughts - machanic is is world class NMRA builder, he also built a car just like mine that has no issues. Please HELP. thanks

 

[nelzfoxes]

Still have a heater core? Maybe clogged? Bypass it? All I could think of.

 

[393LX]

Did that one already. Core is perfect. In fact when we open it, temp drops slightly before climbing again. Worst of it is I live in SW Florida. No room for weak cooling down here

 

[nelzfoxes]

Yeah. I guess that would be one of the first things. Might be engine internal.

 

[MustangIIMatt]

Head gaskets installed correctly?

 

[Bullitt347]

Define "run cycle" and how long is it shut off in between run cycles?

 

[mikestang63]

1. check for air in the sytem
2, thermostat suck closed?
3. what CFM are the fans-do you have a shroud
4. clogged radiator
5, collapsed hose
6. pressure test system?
7. check exhaust gas in coolant
8. what is your timing set at
9. what is your A/F ratio

 

[393LX]

Since we can't keep taking it out on the highway with all the gauges that are hooked up, we are running on the dyno. Basically running it at highway speeds (2-2500 RPM) for about 10-15 minutes and then letting it cool down to idle for about 5 minutes. Then we shut it off and restart after another 5 minutes. Usually after the second cycle, it warms back up and then suddenly the temp gauge wants to peg. We've replaced everything possible and are still at a loss. The folks at Griffin have been consulting with us and say the setup we have should cool an engine of over 500 HP easily.

 

[393LX]

2, thermostat suck closed? We've changed them 4 times at all different temps. We've pulled them every time it overheats and they are fine.
3. what CFM are the fans-do you have a shroud I can't say for sure because I wasn't privy to that. We used the recommended one from Griffin. Has a shroud and all custom ducting up front to ensure that all air runs through the radiator.
4. clogged radiator - a brand new Griffin, flows like a mother.
5, collapsed hose - no and all new
6. pressure test system? - not sure on that, will check with my mechanic
7. check exhaust gas in coolant - not sure on that, will check with my mechanic
8. what is your timing set at - not sure on that, will check with my mechanic
9. what is your A/F ratio[/QUOTE] - not sure on that, will check with my mechanic

Here's what I cannot understand. Why would an engine run fine through a few driving cycles and then suddenly heat up to the boiling point in one minute. It just doesn't make any sense. My mechanic is a real pro and races and builds professionally and he is telling me he has never seen anything like this. It's a mechanical device and there surely has to be an answer. He has spoken to other builders, Griffin, Vortec and has checked and re-checked every suggestion. I've spent a boatload changing virtually everything, all to no avail. My other car runs a Boss 363 making 500 HP with all the same cooling equipment and never overheats. I can idle in traffic with the air on!

 

[nelzfoxes]

Did you do head gaskets recently?

 

[nelzfoxes]

When installed properly one will appear to be upside down. What is important is that the coolant passages in the gasket are at the back of the motor.

 

[nelzfoxes]

I just took these pics of my windsor build.

 

[nelzfoxes]

Head gaskets installed correctly?

Didn’t realize you beat me to it!

 

[mikestang63]

Did you check the radiator cap?
Do you have an overflow and is the hose not crimped?

 

[393LX]

Ok - this is a stock GT motor and has never been opened up. She’s got 60k on her. All the power adders are external. Why do you think I should open the engine when compression and leak down are within specs? I don’t mind doing whatever it takes to cure this issue but so far all I’ve done is throw tons of money at it. If there was suddenly a head gasket issue, wouldn’t there be some other symptoms?

 

[General karthief]

First off even a competent mechanic can make mistakes, but I would think that you would have an overheating problem from the first startup. We had a car come in with the backward gaskets and it would overheat within a few minutes.
Check water pump rotation and try running it without the thermostat, you should check your thermostat opening temp,
Just stabbing in the dark here.

 

[393LX]

Ok - this is a stock GT motor and has never been opened up. She’s got 60k on her. All the power adders are external. Why do you think I should open the engine when compression and leak
down are within specs? I don’t mind doing whatever it takes to cure this issue but so far all I’ve done is throw tons of money at it. If there was suddenly a head gasket issue, wouldn’t there be some other symptoms?

 

[General karthief]

Ok - this is a stock GT motor and has never been opened up. She’s got 60k on her. All the power adders are external. Why do you think I should open the engine when compression and leak down are within specs? I don’t mind doing whatever it takes to cure this issue but so far all I’ve done is throw tons of money at it. If there was suddenly a head gasket issue, wouldn’t there be some other symptoms?

Yes, and the test for fuel in the coolent could show a gasket problem along with the compression and leak down test eliminated that.
And it was not stated as to the miles or the heads where not removed,

 

[mikestang63]

have your mechanic use a laser heat gun while the engine is on- at the radiator hose connections at the radiator and block,, the thermostat, the water pump, the intake, the heads, the radiator,,,,,

 

[393LX]

I’m surely not saying he’s infallible by any means. He’s obviously missing something or it wouldn’t overheat. The big question is what. We have changed numerous caps. All hose are new, no crimps. We tried every temp thermostat, including just a restrictor. The thermostat that seems to behave the best is the 195 for whatever reason. My guy is not too proud to listen to any reasonable suggestion and that’s why I’m posting here hoping to get different point of view. Somebody has to guess or stumble on to it. What it seems to be inching towards by elimination is something in the engine, since all external devices have been rotated, exchanged, etc. Could the blower be causing this? The car never even ran warm when it was stock. You could idle in 95 degree Florida heat with the air on!