# 67 gto hot idle, done everything what now?



## fiesta62 (Jan 12, 2011)

hi, my 67 gto sits on 190 driving but as soon as i sit and idle the temp goes up, today in traffic temp went to 215 before i got moving again, if i had to wait longer it would keep going up etc, i have had the water pump modified to flow better, also installed a new pully to spin pump faster, installed aluminium manifold which should help cooling, installed a coolant recovery tank, and just replaced fan clutch with the hayden severe duty, when i bought car receipts show the harrison rad has been recored with a max flow core , i could install a aluminium rad but thinking that may not change anything as my rad looks fine, i have a hi flow 180 thermostat installed, i thought about electric fans but many seem against this idea so what can i do, any ideas? thanks


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## jmt455 (Mar 26, 2012)

If the temperature is creeping up at idle, it's typically caused by insufficient coolant flow, insufficient air flow, lean air/fuel mixture or timing. It can also be due to a combustion chamber leak that builds heat and pressure in the cooling system.

First of all, make sure there are no combustion leaks.

If all is healthy, then verify timing and air/fuel mixture because they both will create excessive heat that the cooling system cannot remove.

Because your problem is limited to idle operation, you want to verify that your A/F mixture is not too lean at idle AND that the base timing is correct. If you are running ported vacuum for your vacuum advance system, you could experiment with manifold vacuum. Advancing the timing at idle will help it run cooler at idle, but it can lead to part-throttle acceleration stumbles when the throttle plates open. It's been my experience that experimentation is the best way to know if your engine will like to run with manifold vacuum for the advance function.

If all those items are where they need to be, you're back to confirming air flow through the radiator at idle. You don't mention a shroud, but I assume you have one on the car. If not, add a good fitting shroud. Make sure the fan shroud fits properly with no gaps around the radiator that allow air to sneak around the perimeter of the radiator instead of being pulled through the fins.

Also, make sure the fan is positioned properly in the shroud; the blade tips should be 1/2 to 2/3 in the shroud.

The fan diameter should be correct for the shroud opening; the blade diameter should be about 1" to 2" smaller than the diameter of the shroud opening. And of course, verify that the fan pitch is correct for the engine rotation (though if that was wrong, you would have problems all the time).

If you're running a high compression combination with cast iron heads, you might end up needing the aluminum radiator because the cooling system can't handle the heat generated by the engine. BUT, since you don't have a temperature problem under normal driving conditions, you should be able to solve this without needing an aluminum radiator.

I see you also posted on the PY forum. There is an excellent reply there from OldGoat67; his comments are "on the money" as far as the cooling system for stock engines.


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## fiesta62 (Jan 12, 2011)

jmt455 said:


> If the temperature is creeping up at idle, it's typically caused by insufficient coolant flow, insufficient air flow, lean air/fuel mixture or timing. It can also be due to a combustion chamber leak that builds heat and pressure in the cooling system.
> 
> First of all, make sure there are no combustion leaks.
> 
> ...


hi, i posted a lot more info on the py forum, everything is done pretty much as you suggested, engine rebuilt 25,000 miles ago compression is 9.1, stock heads, my mechanic who as i have said knows his stuff feels alu rad or electric fans are definatly not the answer, i have the stock shroud fitted with the 2 bolts either side so not much more i can do there, fan position looks right, friend has adjusted mixture and double checked its all good, we are going to look at adjusting the kick in time of the fan clutch by adjusting the spring, but ideas are running out....


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## fiesta62 (Jan 12, 2011)

4 pics of shroud and fan, fan is 17.5 inchs tip to tip...


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## fiesta62 (Jan 12, 2011)

3 more pics of shroud along base of rad, i been asked if the shroud is sealed to the rad base, as u can see its not sealed and not sealed across top of rad, is this a problem, is this the correct shroud ?


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## jmt455 (Mar 26, 2012)

That fan looks too small for the shroud opening and the shroud looks too small for that radiator.

I'm looking at the radiator and fan usage info in the GTO Restoration Guide.
1967 shrouds were either 9783757 or 9774621. 

The 9783757 shroud is plastic and has a 21 1/2" diameter opening. It was used with a 19 1/2" diameter, 7-blade clutch fan with 2 1/4" pitch. This was the standard setup for air conditioned cars. Ram Air cars used this shroud, but with a 4-blade fixed fan.

The 9774621 shroud is fiberglass and has a 19 1/2" opening. It was used with an 18" diameter clutch fan. This combination was used for cars equipped with the trailering package or for dealer-installed air conditioning.

The radiator for HD cooling or trailering package was 3010454 (TT code).
With A/C, the radiator was part no. 3010455 (TY code)

If that was my car, I would find the largest diameter fan that will fit in that shroud opening, leaving no more than 1/2" clearance between the tip of the fan blades and the inner edge of the opening.

I would also seal the shroud to the radiator.


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## fiesta62 (Jan 12, 2011)

jmt455 said:


> That fan looks too small for the shroud opening and the shroud looks too small for that radiator.
> 
> I'm looking at the radiator and fan usage info in the GTO Restoration Guide.
> 1967 shrouds were either 9783757 or 9774621.
> ...


hi..well my car isnt factory ac, although i have a classic air system that i will be installing soon, so i have the standard 17.5 inch 7 blade fan and stock shroud, exactly as sold by ames i had a look today its on there site...anyway we adjusted spring on fan clutch and removed spacer from fan so fan is not as far into shroud now, pics on other forum, i will test drive tomorrow but if it dont work i am going to search for a 19.5 inch fan and larger shroud thats the next step..... we put a towel in front of my grill with engine running and it barely sucked it towards grill....my mechanic did same test on his 66 gto and wow almost sucked towel thru grill...so i am not getting enough air , and i guess thats going to mean i need a bigger fan !


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## 67GTOCoupe (Mar 6, 2013)

I think your on the right track with the air flow through the radiator with the car standing still. One other typical probelm I have seen with many different makes of cars are aftermarket fan clutches. Many of them just do notwork properly or as someone else pointed out a couple weeks ago they are not tuned for older cars. The operating tempatures of many newer cars is around 215-220 F and the aftermarket fans are often tuned to operate in this manor. Some of the cars built in the last 10 years have an operating tempature as high as 235 F!
If you find your fan shroud fit good up against the radiator and you do not have to big of a gap between the blade and the shroud I would definetely take a good look at the fan clutch. 
Someone here also made mention of being able to adjust the spring on some to get the clutch to engage at a lower tempature but I have never tried that myself.
The paper test on the face of the radiator is a good simple foolproof test. If your car is up to temp and sitting still it should suck a piece of paper right out of your hand and pin it right to the radiator face if the blade and shroud are set up right and the clutch is working properly.


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## geeteeohguy (Feb 2, 2008)

Two things: the shroud needs to be sealed to the radiator, and the fan is too far into the shroud. The fan should be half in, half out. Too far in can result in turbulence and cause airflow problems at idle. As a side note, yeah, the shroud looks a bit small, but if it's sealed it should be ok.


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