Overheating problem

I have a 1978 Anniversary Corvette that overheats at idle. I just had the engine completely rebuilt and made some modifications to increase my horsepower. We bored it 30 over, installed flathead pistons and installed a 262 cam shaft AND aluminum radiator. I have the original fan shroud and air scoop.

Now, I'm in Texas where right now we're running 90+ with 70% humidity. If I run the AC it overheats at an idle (red light), if I don't run the AC it'll heat up but not red line.

HELP, I don't want to install secondary cooling fans if I can avoid it. Any ideas………..

Make sure your radiator is sealed to the core support. All the air that comes in the front you want to FORCE thru the radiator. Even the seal on top of the core support that seals it to the hood. MAke sure you have a good coolant mix, the water pump/fan/t'stat are all OK. Don't forget the hoses too.

I had my BB out today- same weather you have in Tx, I don't have a/c, but it'll run right up to 200* and over if I get above 70. (4000 RPM)

I'd say the biggest thing is the seals on the core support and how good your fan shroud fits.

And read this: http://www.vettemod.com/forum/showthread.php?t=1401

first things first....... you say it's overheating but is it puking coolant out? Have you confirmed the actual temp with an IR temp gun against what the gauge reads?

second, WHEN does it overheat, assuming you confirmed the issue with an IR temp gun.
is it at idle or slow speed driving or on highway driving?
EDIT:: opps, I see it's at idle.

idle or slow speed cooling issues are typically caused by a bad fan clutch, improper timing or vacuum advance.
Highway driving cooling issues are typically caused by either an insufficient radiator, or restricted coolant or airflow.

As mentioned already, make sure ALL the radiator and core support seals are in place, plus, the air dam under the nose is in place, the fan clutch is working correctly, t-stat is opening correctly and fully, timing and vacuum advance are correct, and the lower radiator hose is the correct one with a spring inside it.

because you state it's an issue at idle, to check the fan clutch start the motor and get it up to full operating temp. Shut the motor off and watch the fan. it should stop within 1-3 revolutions. If it takes much longer or completely freespins it's bad.
Again, check timing and vacuum advance for correct setting and operating. What is your initial and total timing without the vac adv connected? Is the vacuum advance connected to full manifold vacuum?

BTW, if it's not puking, what temps are you actually getting? I see MANY threads from people complaining of overheating issues and come to find out the car is running at around 200º.
My 100% stock, 12,000 mile '78 still has all factory emissions equipment including the factory 195º t-stat so runs normally at between 200-210º and with AC on a hot day will run 210-225º. That is NOT overheating or running hot, that is normal and the designed parameters for these cars.

BarryK said:

My 100% stock, 12,000 mile '78 still has all factory emissions equipment including the factory 195º t-stat so runs normally at between 200-210º and with AC on a hot day will run 210-225º. That is NOT overheating or running hot, that is normal and the designed parameters for these cars.

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That's exactly where my stock '82 runs... 200-210 daily... hot day - 210-200.

Okay, I printed all replies and have delivered to the mechanic. He's still thinking the aux fans are the answer.....maybe it's time to take my girl elsewhere. Kind of get the feeling this 'girl' is getting the brush off.

Thanks for all your advise, makes sense to me.

:suspicious:

aux fans can help, but unless you find the real issue (if there really is one) all you will do is mask it.

you didn't answer what temps the car is running and if it's puking coolant or not.

Red 78 said:

Okay, I printed all replies and have delivered to the mechanic. He's still thinking the aux fans are the answer.....maybe it's time to take my girl elsewhere. Kind of get the feeling this 'girl' is getting the brush off.

Thanks for all your advise, makes sense to me.

:suspicious:

Click to expand...

Red, save yourself some money, take the damn thermostat out, and see how it runs.....assuming you have a proper NON LEAKing fan shroud and the fan is GOOD

I have found that mainly STANT brand of thermostats caused me tons of troubles....get that thing TT recomended some time ago, i'ts made of brass, and goes for a VOLVO and designed to fail in the OPEN position....for this latest install I put 3 1/8 holes around the edge of it, to assist in cooling form my non stock install...you maybe want to do that also....

bet it cures your problem....get a MURRAY brand stat....

:banghead::clobbered::drink:

mrvette said:

Red 78 said:

Okay, I printed all replies and have delivered to the mechanic. He's still thinking the aux fans are the answer.....maybe it's time to take my girl elsewhere. Kind of get the feeling this 'girl' is getting the brush off.

Thanks for all your advise, makes sense to me.

:suspicious:

Click to expand...

Red, save yourself some money, take the damn thermostat out, and see how it runs.....assuming you have a proper NON LEAKing fan shroud and the fan is GOOD

I have found that mainly STANT brand of thermostats caused me tons of troubles....get that thing TT recomended some time ago, i'ts made of brass, and goes for a VOLVO and designed to fail in the OPEN position....for this latest install I put 3 1/8 holes around the edge of it, to assist in cooling form my non stock install...you maybe want to do that also....

bet it cures your problem....get a MURRAY brand stat....

:banghead::clobbered::drink:

Click to expand...

sorry, I'll never understand why people recommend removing the t-stat. Unless it's failed and completely closed it answers nothing and if it was a failed t-stat I'd venture a guess that the poster would be posting about having to have his vette flat bedded home. A non-opening t-stat is going to bring the car to a stop on the side of the road fairly quickly.
The same for running a car on a regular basis without the t-stat that some people like to recommend. The t-stat is there not only to help speed up bringing the motor to operating temp to reduce cylinder bore wear but is also a designed and calculated coolant restrictor to allow coolant to flow thru the system at the designed rate. Removing that restriction allows coolant to flow too quickly, detrimental overall to the cooling system.

The Robert Shaw or Mr. Gasket brands are the best t-stats. They are the same, Mr. gasket is just a R.S. unit marketed under their brand name.
These are balanced flow units and if they fail they fail in the open position allowing coolant flow to continue.

Over the years I find the Rob Shaw gave me some troubles to boot....never bought any MrGaskets....

now, over the years I find the hole diameter in the mounting plate is smaller for the 160 stats these days...and the 180's for long time now...same flow as the 195 stat....greatly restricted....want proof of my memory, go get a BOAT engine stat, you find they are rated at 160f and still have the larger diameter opening...but the AUTOMOTIVE ones do not....

all the damn stat can do is open at whatever temp...got news, they don't...they sold as 180f stats and open on the stove in water at sometimes high as 195-200 and unfortunately I"m serious....but that is only 1/2 the problem the flow when open is restricted.....

so what I do to prove the point is remove the stat, and try that for the summertime running, never once failed to significantly reduce the temps....

but then in winter have to put one back to keep temps up

I have found that MURRAY seems to be the most stable brand, here in Florida, so far....

:bounce::smash:

mrvette said:

all the damn stat can do is open at whatever temp...got news, they don't...they sold as 180f stats and open on the stove in water at sometimes high as 195-200 and unfortunately I"m serious

Click to expand...

ummm, that's the way t-stat are suppose to operate. the rated temp is when they are suppose to START to open, not when they are suppose to open fully, that takes a few more degrees of temp.
The rated opening temp, for example a 180º rated t-stat is suppose to START to open at 180º give or take approx 5º or so.
The Robert Shaw 180º unit in my car starts to open at 183º and is fully open by 190-195ºº. This is normal and how they are designed to function.
I've also never had a R.S. unit fail on me.
My car has a restoration DeWitts radiator in it that's approx 10 years old and the rest of the system is 100% original equipment (except for the Robert Shaw t-stat) and it runs consistently at 180-185º regardless of ambient temp.

mrvette said:

....but that is only 1/2 the problem the flow when open is restricted.....

Click to expand...

of course it is, as I explained in my last post a t-stat is SUPPOSE to be a designed restriction. not enough flow obviously is bad as we can all agree on but at the same time an unrestricted flow is too much and can be detrimental to the overall cooling since it flows so quickly without restriction - as fast as the water pump can pump it - it doesn't allow the coolant enough time in the block to absorb heat from the motor.
your statement that your motor runs cooler without a t-stat is proof of this. Remember, the temp sender units measure the COOLANT temp, not what the actual motor temp is (temp of the actual block, heads, etc). You are seeing lower temps without the t-stat in there because the coolant is flowing too fast thru the block to absorb the heat from the motor into the coolant to carry it away and since the coolant isn't picking up the heat the temp sender is showing a nice, low temp but it's really a false reading if you think about it because the heat is still in the motor, just not in the coolant where it should be.
One last comment that warrants repeating since I mentioned it before. The MAIN function of the t-stat is to help the motor warm up to operating temps faster than a car without one. The longer it takes a car to warm up the more wear on the cylinder wall bores and rings.

mrvette said:

....but that is only 1/2 the problem the flow when open is restricted.....

Click to expand...

of course it is, as I explained in my last post a t-stat is SUPPOSE to be a designed restriction. not enough flow obviously is bad as we can all agree on but at the same time an unrestricted flow is too much and can be detrimental to the overall cooling since it flows so quickly without restriction - as fast as the water pump can pump it - it doesn't allow the coolant enough time in the block to absorb heat from the motor.
your statement that your motor runs cooler without a t-stat is proof of this. Remember, the temp sender units measure the COOLANT temp, not what the actual motor temp is (temp of the actual block, heads, etc). You are seeing lower temps without the t-stat in there because the coolant is flowing too fast thru the block to absorb the heat from the motor into the coolant to carry it away and since the coolant isn't picking up the heat the temp sender is showing a nice, low temp but it's really a false reading if you think about it because the heat is still in the motor, just not in the coolant where it should be.


Sorry man, guess we have to agree to disagree.....the water is under pump pressures as well as rad cap.... and it's going to pick up plenty of heat from the engine regardless of speed.....in fact faster flow will over cool the engine....even in summer....proved that way ever before I got a infrared temp sensor....just pop the hood the stick my head over the engine, I can tell a over hot engine from normal running in a flash on MY cars....

the engines never got hot, the intstruments are correct, reading from the heads, anyway.....edit, and if engine was all that hot, oil pressures would drop also....no change once 160f was attained....

:tomato:

well, somehow I've gottom myself in the middle of two different "cooling issue" threads plus now a vacuum advance discussion between here and over on CF, not to mention another thread with a topic I don't even want to think about anymore.... and it's been too long of a day to for my brain to keep this up.

As you say, we will just have to agree to disagree