348 overheating - Impala Tech
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post #1 of 5 (permalink) Old 07-02-2018, 09:11 AM Thread Starter
 
 
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Thumbs down 348 overheating

I have a 1958 and a 1959 Impala. Both have 348's with tri-power and both overheat. I have had the engines rebuilt after one showed combustion gases had entered the coolant. I installed new, 180 degree thermostats, aluminum radiators, Cooling Components electric fans and new water pumps. I run a 50-50 antifreeze mix and have added a can of water wetter. I use 16 lb radiator caps. I have overheating in both city and highway driving. My RPM's at highway speed are in the ranges of 2,300 to 2,500. I am running 32 degrees of mechanical advance. Total advance with the vacuum advance connected is 45 degrees. I have tried running with and without vacuum advance.

I would appreciate any advice as I just don't have any idea of what else to try!
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post #2 of 5 (permalink) Old 07-02-2018, 09:35 AM
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Well timing does affect the temp of the motor, but if you removed the vacuum advance that should have changed it enough to see a difference in temp. The only thing I can think of at this point is plugged water passages in the block. The only cure for that is to pull it completely apart and to boil the block in sodium hydroxide to remove the corrosion.

Big Dave
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post #3 of 5 (permalink) Old 07-02-2018, 10:26 AM
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Quote:
Originally Posted by Jedechnik View Post
I have a 1958 and a 1959 Impala. Both have 348's with tri-power and both overheat. I have had the engines rebuilt after one showed combustion gases had entered the coolant. I installed new, 180 degree thermostats, aluminum radiators, Cooling Components electric fans and new water pumps. I run a 50-50 antifreeze mix and have added a can of water wetter. I use 16 lb radiator caps. I have overheating in both city and highway driving. My RPM's at highway speed are in the ranges of 2,300 to 2,500. I am running 32 degrees of mechanical advance. Total advance with the vacuum advance connected is 45 degrees. I have tried running with and without vacuum advance.

I would appreciate any advice as I just don't have any idea of what else to try!
What is your definition of 'overheat'? Are you boiling over? Or just 'high' temps?

If only 'high' temps, what temps are you getting? At idle? At forward speed?

At idle there is little if any mechanical advance; it is 'initial' plus vacuum. Something close to 24 degrees (+,- a few) is what I would call 'typical'. At speed, vacuum advance is nil, timing is 'initial' plus mechanical. If you are 45 degrees BTDC at idle, that looks quite high to me. I don't know what your specific engine needs, nor how it was built. But 45 at idle is way more than GM did.

One thing to try is simply retard your 'initial' timing to around 12 degrees BTDC (with the vacuum advance disconnected and plugged off). Attach the vacuum advance and see if you get up around 24 degrees BTDC, at idle. See if that runs well and reduces your temps. It's free and be be undone easily.

I personally am not a fan (no pun intended) of the electrical fans. A mechanical fan installed properly in its shroud works quite well. It allow full air flow thru the radiator at forward speed and pulls enough air thru the radiator at idle to keep temps within an acceptable range.


Pete

Last edited by japete92; 07-02-2018 at 10:42 AM.
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post #4 of 5 (permalink) Old 07-10-2018, 08:43 AM
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The 1958 348 did not have some of the steam holes on the heads that were added later due to overheating issues the engine was having. If you are using a later set of heads that don't have these passages filled then you will overheat something terrible. If your 1959 is an early manufacture date it could be the same way, or if you use a set of 1958 heads that due not have the cooling passages on a block that does it creates heating issues.

The 1959 engine block and heads were re-designed with cooling around the plugs as this was the hot spot on the 1958 engine. If when you had the engines rebuilt they put the 58 heads on the 59 and vice versa this would be a major heating issue. Also head bolts on these engines are required to have thread sealant as the head bolt holes are open to the water jacket in the block.

I've got a 1960 348 block that I am building as a 438 stroker. When rebuilding these motors the best thing you can do is replace the pistons. The stock pistons are well over a pound each. New after market pistons are slightly lighter. I think the each rod and piston combo on my engine weighs in around 634 grams. That is pretty heavy compared to SBC and BBC engines, but a lot lighter than a stock piston and rod combo for a stock W motor.
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post #5 of 5 (permalink) Old 07-15-2018, 01:52 PM
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With most heads there is a difference in the cooling passage holes that will be partially obstructed if the head gasket is not installed correctly. Professionals should know this (I thought that you had mentioned that you had it professionally rebuilt), and I only mention it because of your problem with a freshly built motor.

When using GM 10105117 0.028" compressed factory service parts head gaskets (this is for a SBC 350, but same applies to a 348 head gasket) the part number should be facing up and dimpled (stamped) side down. With a FeL-Pro gasket there will be a front stamped into the gasket. Believe it is the same with Mr. Gasket gaskets. Victor gaskets have only a part number which should be facing up.

The front is the side of the engine that has the belts on it (called the front on a rear wheel drive motor, but it can be confusing on a motor that rides side saddle). Fords and many other brands have a tab that should be visible sticking out under the front of the head with the head installed. Most mechanics beat those tabs down to prevent getting cut by them latter on; so you may not see it sticking out if the motor is covered in grime.

Once again apologize as I thought you had it professionally rebuilt; so I missed the fact that you might have done this yourself.

Big Dave
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