Thread: 348 Running warm

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How much does it take to cool these things? It is pretty well stock with a 1406 Edelbrock carb and a 4 core Champion aluminum radiator. It seems to cool fine at first for about 4 miles but then just like it can't keep up and it will slowly clime to about 220 on a 90 deg day. The weird thing is even when I stop to let it cool down, it really doesn't do that well either. I have sit and idle with electric fan running full bore it takes forever to cool. Timing is about 15 base and 40 at 2500. I have my heater hose looped right now, could that be cavitating the pump at all , shouldn't be so complicated. The carb was running lean so I swapped the primarys and that seemed to maybe help a little, down to 210 but its a different day too. Changed thermostat right away and that did not help at all. If my radiator can't handle this thing, you'll see a 348 for sale and a 6.0 put in my 53, I've come to the part of my life where I grow tired of fighting things

Originally Posted by 53 Chevy5

Timing is about 15 base and 40 at 2500.
The carb was running lean so I swapped the primarys and that seemed to maybe help a little, down to 210

15 initial and 40 total tells me you did not disconnect your vacuum advance when you set the timing and your timing is retarded.
When I set timing I always set it by total timing at 4000rpm with vacuum advance disconnected and hose to carb plugged, SBC 32-36° total (you'll have to look up 348). The initial timing will be whatever the distributor allows after total timing is set, usually 12-16°, some distributors require adjustments.

Lean mixture will also cause overheating, however get your timing correct first, then adjust carb.

If you don't have a temperature gun buy or borrow one and verify the temperature gauge is reading accurately (especially if it's an electric gauge). I've run into a couple over the years where the only problem turned out to be the gauge.

I agree with what 36 Sedan says and that should probably be your next step..

If that doesn't completely cure the problem here are a few other things that will probably help. I fought heating issues on my 58 Chevy for the first couple of years I was driving it. Changing fans, the radiator and a few thermostats it turns out the problem was air was backing up in the engine compartment (I had installed the factory control arm seals when I built the car. Removing them to allow the air out cured the problem.

Aftermarket electric fans are also not my favorites. A lot of guys seem to have better luck adapting factory electric fans to their projects but the down side is they usually take up a lot more space than the aftermarket ones. My own personal preference is a factory 7 blade fixed fan on a thick HD fan clutch with a good fan shroud.

If push comes to shove you might also look at a different radiator. I bought one of the 4 row champions a few years back. The problem is the tubes are usually only 3/8" wide, which gives you about 1 1/2" cooling surface as opposed to 2" with a 2 row with 1" tubes. I ended up replacing the 4 row with a Champion 2 row (1" tubes) (same physical size) and the temperature going down the highway dropped 10 degrees.

Rather than completely revamping the cooling system all at once, (as my last suggestions would require), do one change at a time and see what works.

As Denny says pictures would help (and besides I'd love to see that 348).


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I'll try to get some pics tonight for you guys,.I'll recheck the timing also and make sure it's all good. Should the vacuum advance be plugged into constant vacuum or port vacuum after it's timed?

I would use manifold (constant) on your motor, it will add timing at idle and help cool it. But be aware it will raise the idle speed 200-300rpm, nothing to be alarmed about, just wanted you to know so you didn't think something was wrong. You'll probably have to re-set idle speed after it is plugged in (normal).

Not taking away from these other guys as they have good things to follow but this has helped me on some other cars diagnosing issues. My engine overheats, what should I be looking for? to cool a motor to give up on, Matt

Nobody (else) EVER recommends an oil cooler.
The cooling system SHOULD keep proper operating temperature. BUT- custom system can overwhelm engineered standards.

There is no downside to cooling the oil.

Disconnect the vacuum advance and plug it for setting the timing.

Here are some pics, the water pump does have a reversed impeller to run backwards for the serpentine belt.

I do know to disconnect and plug the port for the advance for base timing , but one thing I never understood is I think that the port vacuum is the factory spot, so I always wondered what the advance weights in the dist are for. To add to that , then I never am quite sure if total advance should checked with the vacuum hooked up or not. From what I understand now, use the weights for total advance and plug the dist to constant vacuum after its all timed.

I have got one small thing to check, this problem happened to me, badly and caused me a ton of grief, if you happen to have a similar hi flow thermostat and they dont have room to expand, or the water doesnt have room to go around the outside, which could be a possibility on some motors https://m.youtube.com/watch?v=mvZ1UunKGqI

Originally Posted by firebird77clone

Nobody (else) EVER recommends an oil cooler.
The cooling system SHOULD keep proper operating temperature. BUT- custom system can overwhelm engineered standards.

There is no downside to cooling the oil.

It has crossed my mind but if I have to go that route or revamp my whole cooling system, the 348 is going to a new home and a 5.3 or 6.0 will go in it's place this winter. It's a cool motor, but honestly, I would feel a little more comfortable driving this thing across the states with a modern motor if this thing is going to fight me.

Originally Posted by 53 Chevy5

It's a cool motor, but honestly, I would feel a little more comfortable driving this thing across the states with a modern motor if this thing is going to fight me.

JMHO, I think you're fighting the indefinable. If you’re anything like me, you may as well start now and put the motor in. Get your piece of mind and enjoy!

Originally Posted by Matthyj

I have got one small thing to check, this problem happened to me, badly and caused me a ton of grief, if you happen to have a similar hi flow thermostat and they dont have room to expand, or the water doesnt have room to go around the outside, which could be a possibility on some motors https://m.youtube.com/watch?v=mvZ1UunKGqI

Great info! However, it appears he is installing the stat upside down???

Originally Posted by 53 Chevy5

I do know to disconnect and plug the port for the advance for base timing , but one thing I never understood is I think that the port vacuum is the factory spot, so I always wondered what the advance weights in the dist are for. To add to that , then I never am quite sure if total advance should checked with the vacuum hooked up or not. From what I understand now, use the weights for total advance and plug the dist to constant vacuum after its all timed.

I do know to disconnect and plug the port for the advance for base timing.
Great!

but one thing I never understood is I think that the port vacuum is the factory spot.
Pre 70’s cars used manifold vacuum advance (all of the muscle car years), the 70’s brought us the SMOG motors (de-tuned) and the vacuum advance was moved to port or timed vacuum source (above throttle, no vacuum at idle) to raise idle temperatures and burn hydrocarbons.

so I always wondered what the advance weights in the dist are for.
Mechanical advance, allows the motor to start easier and helps in tuning the power curve for street use, race motors are locked out (no mechanical advance).

To add to that , then I never am quite sure if total advance should checked with the vacuum hooked up or not.
Vacuum disconnected.

From what I understand now, use the weights for total advance and plug the dist to constant vacuum after its all timed.
Correct! There are times with some motors that using the ported vacuum is advantageous. Some motors use no vacuum advance as it has nothing to do with horse power but rather economy.