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350 sbc running hot on highway

24K views 25 replies 11 participants last post by  406 bug 
#1 ·
I have a 350 in a '32 Chevy sedan with a th-350 tran. behind it. 3:55 rearend. Runs 180-185 in town, stop and go w/o air on, runs 190 with air in same situation. Go out on the highway and after 15 or so miles at 60-65 mph, the engine temp starts to go up and seems to run about 225 or so. Gets hotter if a semi gets in front of me. I have a hayden elec. fan on it. Don't know what the cam is but the engine is a 1969 vintage with Edelbrock manifold and 500cfm carb on it. Stock distributor with pertronix flame thrower II conversion in it and high voltage coil. How can I tell if it's timing (too retarded), to lean, air flow, or radiator? This is a real stumper for me. Where to go from here as I've done all the basic testing. I did back the timing off a bit after it was running hot and causing ping when accelerating.

Thanks
 
#2 ·
Are you still running the hood sides?? Might try removing them temporarily to see if it is and airflow/air escape problem. If the hot air can't get out of the engine compartment after it goes through the radiator it is as bad as not having enough airflow or enough radiator size.
 
#4 ·
Running hot

Running a brass/copper radiator, cannot tell brand. I believe it was not the original. It has tranny cooler in bottom. I have an aftermarket chrome water pump, again no brand or model #. (I bought this car and it had been in storage at least 5 years or more, old build) As I said elec. fan thermostat in bottom of radiator tank.

Yes the hood is on, but not stock it is louvered top and sides extensively, but still could cause a flow problem. Good suggestion, I'll try it without the hood and see what happens.
 
#6 ·
My car would do something similiar to this. After checking over the whole system and finding nothing, I went back to what I started with, the T-stat. It was a new 180 degree unit. In town, ran 190, get on the interstate and do 70 the temp would climb to 230 which made me uncomfortable. I checked the stat in boiling water, opening temp great, closing temp off, after the water cooled down past 150 the T stat was still wide open, down to 120 still wide open. Got a new one, tested it before I installed it, it too was bad, next checked out good so I used it. I`ve found over the years the quality of T stats has really went down, I even tried the high dollar 6 bucks a piece jobs to find they too were bad right out of the package. Check your T stat, it may save you a lot of work.
 
#10 ·
Fan / radiator answers

1BAD80 said:
Is there a fan shroud covering what the electric don't?
No, there is no shroud
How much of the rad is open on the motor side ?
Basically the whole back side is open to the engine. The fan is there set up as a puller.

Check what DV said also.

Plus put a 1/8" hole in the thermostat it helps any cavitation & air pockets.
Any pics ?
Pics will be attached.
 

Attachments

#11 ·
I would guess 1 of 4 issues listed in order of probability

1, Too little air flow through radiator or it is undersized.
2, Internal cooling system pressure holding thermostat closed.
3, Radiator hose sucking shut at highway speed.
4, Ignition timing retarded
 
#12 ·
Thanks for suggestions

T-bucket23 said:
I would guess 1 of 4 issues listed in order of probability

1, Too little air flow through radiator or it is undersized. Possible

2, Internal cooling system pressure holding thermostat closed.
Running a 7-8 lb cap and it does not blow off through the overflow. If I watch the temp guage, as it goes over 180 to around 190, the temp then will drop back to 180 in about 30 seconds, so I think it is opening.
3, Radiator hose sucking shut at highway speed.
Brand new hoses for top/bottom/heater core.
4, Ignition timing retarded
This is where I'm going right now. Also, checking lean and vacuum stuff. Then to #1 with hood off trial at highway speed.

Thanks again.
 
#13 ·
I see green mold outside the radiator. That radiator needs to be either replaced or boiled out. Some of the tubes may be clogged from letting it sit around. I wonder if tubes in the radiator are more efficient horizontally then vertically. I read an article a while back it's more efficient running the tubes horizontally. I do not know of that is true.
 
#14 ·
Jim7231 said:
This is where I'm going right now. Also, checking lean and vacuum stuff. Then to #1 with hood off trial at highway speed.

Thanks again.
I will be surprised if the hood make a difference at highway speed if you are not having issues in the city. A water cooled engine does not rely very much if at all on block surface cooling from ambient air.
I have seen several vehicles that don't have the heater connected and the block plugged that the internal pressure keeps the thermostat from opening.
 
#16 ·
air flow

T-bucket23 said:
I will be surprised if the hood make a difference at highway speed if you are not having issues in the city. A water cooled engine does not rely very much if at all on block surface cooling from ambient air.
I have seen several vehicles that don't have the heater connected and the block plugged that the internal pressure keeps the thermostat from opening.
What I was wondering about is at highway speed, if there was not adequate "venting" of the engine compartment, could a pressure front build up such that the flow through the radiator could be reduced?
 
#18 ·
Jim7231 said:
What I was wondering about is at highway speed, if there was not adequate "venting" of the engine compartment, could a pressure front build up such that the flow through the radiator could be reduced?
It is possible I suppose. I would think the air rushing under the car would suck the engine compartment air out as it would create sort of a vacuum. The is usually plenty of room around and under the engine for air to escape.
The bottom line is air has to move through the radiator to cool the fluid. Anything restricting this or causing the air to go around the radiator would hinder cooling. Some fans will actually reduce the forced flow of air at highway speeds. I have seen some very subtle changes to mounting or grill design solve cooling issues.

Over heating issues are hard to diagnose without having the car. A remote sensor on the radiator can also tell if the radiator is the issue of if the cooled water is not reaching the engine for some reason like a collapsed hose
 
#19 ·
T-bucket23 said:
It is possible I suppose. I would think the air rushing under the car would suck the engine compartment air out as it would create sort of a vacuum. The is usually plenty of room around and under the engine for air to escape.
The bottom line is air has to move through the radiator to cool the fluid. Anything restricting this or causing the air to go around the radiator would hinder cooling. Some fans will actually reduce the forced flow of air at highway speeds. I have seen some very subtle changes to mounting or grill design solve cooling issues.

Over heating issues are hard to diagnose without having the car. A remote sensor on the radiator can also tell if the radiator is the issue of if the cooled water is not reaching the engine for some reason like a collapsed hose
I assume by remote sensor you mean a temp sensor connected to a display or ? in the car. I may be able to do that and that's a terrific idea. I really want to know the cause and not purchase a radiator or something that may not be the problem. Ok, I'm adding a remote temp sensor to my list of things to do.
Thanks.
 
#20 ·
To set the timing for max vacuum-

Unhook the vacuum advance. Plug in a vacuum gauge to a manifold source. Turn the engine on. Now turn the distributor counterclockwise to advance it until you reach peak vacuum, and you are done.

You might have to re-curve the distributor's mechanical advance for less total advance if detonation occurs. I had to do that with my BBC, though they like more initial advance. Had 22 initial plus 38 mechanical advance, not good.
 
#21 ·
sbc running hot on highway update

Well, I had the radiator (Walker 4-row) rebuilt at a radiator shop. Lots of stuff plugging the tubes he said. Now it really is nice at slow speeds, the electric fan even cycles off idling showing much better cooling (93 degrees outside temp). Still need to test on a long highway run, but expecting that this fixed the weird problem.
Thanks for all the help you guys provided, I learned a whole bunch!

Jim
 
#23 ·
Jim7231 said:
I have a 350 in a '32 Chevy sedan with a th-350 tran. behind it. 3:55 rearend. Runs 180-185 in town, stop and go w/o air on, runs 190 with air in same situation. Go out on the highway and after 15 or so miles at 60-65 mph, the engine temp starts to go up and seems to run about 225 or so. Gets hotter if a semi gets in front of me. I have a hayden elec. fan on it. Don't know what the cam is but the engine is a 1969 vintage with Edelbrock manifold and 500cfm carb on it. Stock distributor with pertronix flame thrower II conversion in it and high voltage coil. How can I tell if it's timing (too retarded), to lean, air flow, or radiator? This is a real stumper for me. Where to go from here as I've done all the basic testing. I did back the timing off a bit after it was running hot and causing ping when accelerating.

Thanks
This is symptomatic of not enough coolant flow getting thru the core as a result of corrosion or crud plugging the passages. At lower speeds and RPMs where the BTU transfer is less, the engine operates at proper temps as sufficient coolant is passing thru the core. When the heat transfer demand increases and the RPMs come up, the returning coolant can't pass thru the core in quantities sufficient to feed the pump's demand. Pump head pressure increases with-in the engine and in the return tank of the radiator but falls within the core, lower tank, and ahead of the pump where the restiction of the core simply can't feed the pump's demand curve.

The core will have to be cleaned or replaced depending on how clogged up it is and how coolant tight it is. Many old cores sprout leaks everywhere when the corrosion and crud is cleaned out.

Chrome looks nice but greatly inhibits heat transfer. I'd limit it's use to places where it doesn't matter in engineering terms like license plate bezels.

Bogie
 
#24 ·
When you have time or money allows think about purchasing and installing a FlowKooler water pump impeller modification kit. It makes a high flow water pump out of any OEM or after market pump. Also use a water wetter solution.

As mentioned earlier about the quality of T-stats, I concur totally. Recently when I was doing a cooling system service on my 04 Tahoe I had a real problem finding a T-stat that was not made in China. Not at NAPA, not at Autozone, not at Car Quest, but found one at Oreilly. He listed two, one made in China and one made in Israel of all places. I took the one made in Israel and it is working fine.

Vince
 
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