Overheating and can't figure it out...

shane416ex · Aug 13, 2009

I built my 79 yota with all the goods but my problem right now is the sbc 350 in it. I can't keep it cool. The motor is stock, and I have a summit aluminum radiator that I have put in the bed, now it's in the front, brand new water pump so thats not it, new thermostat so that shouldn't be it, new hoses that are not collapsing so probably not that. I have had this motor in a blazer that I wheeled for a while and never had a problem, and that was with a stock radiator and just a mechanical fan, now I have a 1,500 cfm electric fan but it doesn't do the job. The motor sat a while during the build but was always inside. But could there be some type of blockage inside??? Could the radiator cap pressure be an issue? (the cap is also new) Any other ideas???

TreeClimber · Aug 13, 2009

Check for air pockets due to rear radiator - front engine. You may have to lift either the front of the rig or the rear of the rig in order to 'burp' the system

Check for CFM of the cooling fan. Check for the volume of the radiator. When a stock radiator sits in the front of the rig, it's got a giant grill to hide behind, so it's quite large. Most aftermarket radiators are significantly smaller, so the fan pulls less air AND there's significantly less coolant in the system.

And just for kicks and grins, make sure the fan is pulling air the correct direction thru the radiator. Nothing like having a pusher fan set up in a puller scenario.

JOOP · Aug 13, 2009

shane416ex said:
I built my 79 yota with all the goods but my problem right now is the sbc 350 in it. I can't keep it cool. The motor is stock, and I have a summit aluminum radiator that I have put in the bed, now it's in the front, brand new water pump so thats not it, new thermostat so that shouldn't be it, new hoses that are not collapsing so probably not that. I have had this motor in a blazer that I wheeled for a while and never had a problem, and that was with a stock radiator and just a mechanical fan, now I have a 1,500 cfm electric fan but it doesn't do the job. The motor sat a while during the build but was always inside. But could there be some type of blockage inside??? Could the radiator cap pressure be an issue? (the cap is also new) Any other ideas???

I think you answered your own question.:eeek:

Make sure you don't have any air trapped behind the Thermostat. Try running it without a thermostat and see if it still overheats.

shane416ex · Aug 13, 2009

And yes the fan is pulling just like it's supposed to. Forgot to mention that before. I may have confused everyone before, the radiator is now in front so air shouldn't be a problem. Or at least not a problem after the thermostat opens up. And another fyi, I let it run quite a while without the cap to let all air burps out of it.

WHITE TRASH1 · Aug 13, 2009

I played that game before... Point the nose up hill and pull a heater hose and fill the system through whatever is the lower point, either the hose ot nipple on the intake/water pump. Once the air is out pop the hose back on and be done.

nevada · Aug 13, 2009

how big is the fan, in relation to the radiator? does it cover it?
and what size is the rad?
how many, and what size of cores?
brass, or aluminum?

what temp of stat are you running?
how hot is it getting?

TreeClimber · Aug 13, 2009

shane416ex said:
And yes the fan is pulling just like it's supposed to. Forgot to mention that before. I may have confused everyone before, the radiator is now in front so air shouldn't be a problem. Or at least not a problem after the thermostat opens up. And another fyi, I let it run quite a while without the cap to let all air burps out of it.

I'm running two similar rigs. Both run hot.

My YJ is AMC 401
My TJ is Chevy 350.

The reduced size of the grill dictates the size of the available radiator. Since the radiator is significantly smaller than the original application (full size truck), you must compensate for the smaller radiator by pulling an abundance of air. I've built massive shroud to force ALL available air to flow thru the radiator. I've gone to the largest available fan to force ALL available air thru the shroud. I even had the lower radiator hose location moved wider on the radiator so that I could run a bigger fan.
I've gone to a pusher electric fan in front and a mechanical puller fan behind the radiator. I even louvered the hood of the YJ as the AMC ran hotter than the Chev

At this time I don't run hot at all in the Chev, and rarely in the AMC. But it's only in hot weather and on long hauls

Fordzuki · Aug 13, 2009

You can put a flush kit in and barely crack the cap, this makes it easier to get the air out, plus you can usually stretch the heater hose up enough to be the highest point in the system.

I agree take the thermostat out till you get the problem fixed it will help in getting air out also, since an air pocket near the thermostat may make it not open properly.

While the fan is blowing the right direction, are the fan blades facing the right direction to maximize flow? A good aftermarket fan will allow you to flip the blades over between push and pull. It's not as easy as just reversing the wires.

Damnyankee · Aug 13, 2009

1500cfm is not going to cut it.

find one thats about 3k

PUO-BANNED · Aug 14, 2009

go to the junk yard and find a 2.8/3.1/3.4 litre GM passenger car (lumina malibu) and rob the coolant bleeder screw. Leave it open when you fill the system. you can also drill a hole in the t-stat. You want the radiator cap to be the highest point in the system but this doesn't guarantee you will get all of the air out.