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Old 06-04-2006, 01:46 PM
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How hot is too hot?

Howdy guys!

I've got a 68 Firebird with a newly rebuilt 462 (455 + .030 over) in it with an aluminum radiator and new clutch fan. Yesterday, I was out on the road and I ended up idling in gear for about 5 minutes (very long stop light, actually that and an accident). The temp rose to 220 and I pulled off the road and shut the engine down as I was afraid of doing damage to it. Now this is in Las Vegas and the air temp yesterday was around 100 degrees with no wind.

My question is: How hot can you let your engine get before it is too hot? I was guessing that 220 is about the limit.

Jerry

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Old 06-04-2006, 03:56 PM
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used to live there 220 isnt to bad but if your not carfull it can sky rocket out of control
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Old 06-04-2006, 04:14 PM
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Quote:
Originally Posted by henkelphoto
Howdy guys!

I've got a 68 Firebird with a newly rebuilt 462 (455 + .030 over) in it with an aluminum radiator and new clutch fan. Yesterday, I was out on the road and I ended up idling in gear for about 5 minutes (very long stop light, actually that and an accident). The temp rose to 220 and I pulled off the road and shut the engine down as I was afraid of doing damage to it. Now this is in Las Vegas and the air temp yesterday was around 100 degrees with no wind.

My question is: How hot can you let your engine get before it is too hot? I was guessing that 220 is about the limit.

Jerry

220 might be OK with a good pressure cap, and synthetic oil, but prolonged stopping is headed for trouble since it will continue to rise.

I would look into the fact that the temp went up when stopped = lack of sufficient airflow.

1) Check to see that the shroud is air tight over the entire radiator area.
2) Be sure the water pump is overdriven
3) Be sure the thermostatic fan clutch is actually working = MUST HAVE THE SPRING ON THE FRONT (have seen new ones poorly calibrated). and you have 7 blade fan with lots of pitch to the blades.
4) Be sure the fan is only 3/4 inch into the shroud and not recirculating hot air forward off the blade tips,
5) be sure that the fan is not sucking hot engine compartment air back into the front of the radiator.

a) That the radiator is tight to the core support,
b) Seal the top of the core support to the hood.,
c) Seal the bottom of the core support to the front of the air dam/splash pan, use an air dam below the core support to prevent the air from moving forward to be recirculated,

You could build an air tunnel from the core support to the grille.

6) help the hot air get out of the engine compartment by raising the back of the hood as a test, louvering the hood, or using a cowl hood. Remove that rubber seal between the rear of the hood and the cowl.

If you get trapped in that situation again,
1) turn off the AC
2) turn the cabin heater on full blast..... it is a minature radiator.
3) rev it up to 2000 rpm and watch the gauge.

Of course you have cold air induction on your carb intake..... right?

Last edited by xntrik; 06-04-2006 at 04:21 PM.
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Old 06-04-2006, 04:34 PM
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What Xntrik said. However, just for the record the last 5 clutch fans I`ve bought have all been defective, Make sure you know how they operate.
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Old 06-04-2006, 05:41 PM
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220 is not that hot, as an example the Corvettes over the last 10 years and more have elec fans that do not come on till 230 for the 1st fan and at 250 the 2nd fand comes on. but, there is no reason for a car with a mechanical fan to get that hot unless the cooling system has a problem. check the things already mentioned.
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Old 06-04-2006, 05:51 PM
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One more thing to consider.

Some cars had restrictors in the heater hose if they were full flow systems, (no water shut off valves). 1/4 inch diameter holes. This did 2 things. It prevents the water pump from blowing up the heater core and it also reduces summer cooling. This water flowing all summer through the unused heater is NOT being cooled, it is bypassing the radiator.
I prefer a manual shut off controlled by a pull lever.

Any trans cooler inside the radiator tank should not be much of a problem.
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Old 06-04-2006, 08:53 PM
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As long as the coolant doesn't start boiling, its fine to however hot you want to make it. The more important factor is the oil temp. Oil temps over 230 for regular oil and 250-270 for synthetics is danger zone.

I have non-aqueous coolant and I've seen 285 a few times, but my oil temp gauge never went past 220 thanks to an oil cooler.
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Old 06-05-2006, 12:03 PM
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Thanks for the info guys.

What I'm going to try right now is to make sure the shroud is sealed all the way around the radiator, look into a lower air dam and try Water Wetter in the radiator. If that doesn't work, I guess I'll have to look into an electric fan setup. I don't have any problems with cooling when the car is moving, just at idle.

I will also look into setting up an oil temp gauge and perhaps getting an oil cooler, although I don't really think that is a problem at this time.

Jerry

adding this a bit later than the rest of the post:

Would wrapping the headers with heat wrap material help?

Last edited by henkelphoto; 06-05-2006 at 03:01 PM.
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Old 06-05-2006, 03:49 PM
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Quote:
Originally Posted by henkelphoto
Thanks for the info guys.

What I'm going to try right now is to make sure the shroud is sealed all the way around the radiator, look into a lower air dam and try Water Wetter in the radiator. If that doesn't work, I guess I'll have to look into an electric fan setup. I don't have any problems with cooling when the car is moving, just at idle.

I will also look into setting up an oil temp gauge and perhaps getting an oil cooler, although I don't really think that is a problem at this time.

Jerry

adding this a bit later than the rest of the post:

Would wrapping the headers with heat wrap material help?

Water Wetter will not help. You don't have a temp problem all the time. It is a low speed air flow problem. If the temp is rising it will continue to rise because the cooling system cannot keep up.

You must either, cool the airflow, increase the airflow, increase the coolant exposed to the air by a bigger radiator, ...or by pumping more coolant through the radiator.

Electric fans will make the situation worse. Few electric fans will pull the air that a 7 blade x 18 inch with a fan clutch will pull at 1000 rpm. Usually about 50-60% of the volume.

You need to be sure that your water pump is overdriven, as much as 20% is good. That will also turn the fan faster as well as pressurize the block for less steam pockets.

If the fan clutch checks OK..... I would try to find a 7 blade factory fan with more blade pitch. Roaming around the salvage yard carrying your old fan for comparison is a good idea. That worked for me on my Buick V8. A blade with more pitch completely eliminated by problem.

The only way header wrap will help is to reduce the amount of heat that might be sucked back into the front of the radiator. Yes it will make the engine compartment cooler, but that air in there is already behind the radiator and of no consequence otherwise.

Another test: Drive it and recreate the situation. Open the hood and see if the problem goes away.... If all the heat is going UP instead of down and being recirculated, you know what needs attention.
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Old 06-05-2006, 05:04 PM
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thanks for the reply, you've given me a number of things to look at. I'm not sure I can find a pully that will overdrive my water pump...parts for pontiac engines are not as easy to come by as for chevys. But the fan is a good idea. The one I now have is a 6-blade 19".

Jerry
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