overheating 87 4.0

well today my 87 4.0 overheated on the way to work. It was idleing for a little while (in line for the drive through, what can I say) and it started to go up to the redzone. I pulled it over and the expansion tank was boiling over. Also I noticed some steam coming from the radiator (87 renix closed system, no rad cap) so I am thinking I deffinatly have a leak in the rad. I have never had it overheat on me at speed, so I am not quite sure what the problem is. The thermostat is fairly new (1year old or so from the dealership but who knows could be a stuck thermostat) and the coolant was added last summer (I did burp the system as well) but I'm not sure whats causing it. It is possible that because I had that unnoticed leak in the rad that it could have been low on coolant, but I am also thinking that there could be an issue with the clutch fan not working since its overheating at idle (I'm from eastern Nova Scotia, the temperature today is maybe 6*C so its not really a hot day). I have to make a 12km drive back from work at 1 in the morning tonight so anyhelp would be appreciated. I am going to tighten one of the hoses on my lunch hour (the one on the bottom of the expansion tank looks like it sagged down a bit) and I am going to get someone to follow me home.

I'd say prolly low on coolant from leak that went unnoticed-- fill her up and keep an eye on it on the way home. Needless to say (so I will anyway) fix the leak when you get home.....

yeah deffinatly, I am not to sure exactly what is leaking but I have a suspicion that it might be a crack in the side of the plastic of the rad (it still has the factory low-grade plastic sided rad). I may pull her off the road for a little while. Another stupid question but how much more coolant should I add, after it overheated, I put 2 liters into it and have another liter unopened in the jeep. That was halfway between home and work (I had someone take some coolant out to me). I need to tighten that hose and lunch time and I think I will pick up another jug of coolant.

Don't forget to check the plastic canister by the firewall. These are prone to cracking.

Sounds like it's time for a cooling system overhaul.
I did it to my '87 about 6 months ago and have had ZERO issues out of it. It can idle on the trail all day long and it's fine. Just do it, you'll be happy you eliminated potential problems.

yeah I am aware that they crack, mine MAY have a crack along the mold line but I have never seen it leak. I am thinking about converting it over to an open cooling system.

BruceB83 said:

Sounds like it's time for a cooling system overhaul.
I did it to my '87 about 6 months ago and have had ZERO issues out of it. It can idle on the trail all day long and it's fine. Just do it, you'll be happy you eliminated potential problems.

Click to expand...

what kind of a rad did you use, and did you switch over to an electric fan, those are things that I have been thinking of doing. I may be doing the whole engine this summer, I plan on taking the jeep off the road (as in putting it in the garage) for a few months and doing a whole top and bottom on it. Need to touch the body up a little bit cause its beem through 3 winters since the restoration.

You've overheated, so replace the thermostat as well.

When you do, drill two 1/16" or so holes (2-3m/m should also work) in the flange 180* apart. Install with one hole at 12:00 and the other at 6:00, and the system will be able to purge itself if it gets an air pocket.

Treat this point as important. The RENIX system is known for getting air pockets behind the thermostat if it "steam voids," and getting rid of them is a pain - unless you drill your thermostat in the manner I mentioned - then it solves itself. I also suggest doing this with the "open" system...