Overheating going uphill at Hiway speeds

[CowboyX]

So the CJ is overheating, but so far only at highway speeds going uphill in the mountains. Highway speed=60-65 @ around 3k. The cooling system was NASTY when I bought the jeep. Believe the PO ran it with straight water and let it sit for years. I’ve replaced the thermostat and the radiator and the symptoms haven’t changed. I’ve noticed that if you start the jeep with the radiator cap off, once it warms up and the thermostat opens, water pours / bubbles out the radiator neck at a good clip (at idle). I always thought that at idle you can leave the cap off and you shouldn’t lose any water, assuming of course you had the cap off before the system warmed up and pressurized; maybe I thought wrong. The Jeep starts and runs smooth. About a ¼ cup of water runs out the exhaust on startup but never any appreciable white smoke. Doesn’t seem to be losing any coolant (I haven’t let it actually boilover).

I’m suspecting the head gasket but wanted to get some feedback. No signs of water in oil. I have not checked for gases in cooling system or done a compression test yet. A gear head I know suggested that the timing might off and that is causing the issue when the engine is under load and / or vacuum is low. Thoughts?

86’ CJ7
GM 350 TBI
GM Turbo 400 Transmission
Dana 300
4.11 gears

 

[Saddle Tramp]

A couple of thought I have- When you said that the coolant was “bubbling” out with the radiator cap off did you mean you see bubbles in the coolant or just that the coolant overflows the radiator? Bubbles in the coolant would indicate a bad head gasket; it could still be the head gasket even if you don’t see bubbles. If the cooling system was abused maybe the water pump is gummed up and not pushing water properly. If so then the heavy load of going uphill could be too much heat for the for the amount of coolant passing through the radiator to handle. A proper coolant flush of the block wouldn’t hurt either.

 

[gert]

Looks like a good time to get to know your Jeep I see that you posted it being a GM 350 with TBI on it. Is the radiator big enough? Is the radiator fan big enough? sealed to the radiator to pull enough air through the rad? Is it a flex fan with weak blades? is the engine running lean? a good time to do a compression check and leak down check on the clyinders to check for blown head gasket. What is the timing set at? any of the above can make it run hot and its hard for us to tell from here