Howdy, and welcome to the forum! The head gasket will never leak into the exhaust manifold. BUT, leaking into the "water jacket" (coolant) will do as just you say, "cause it to run hot quick"

Hello - I have an '87 XJ 4.0. It's the closed system with no radiator cap. I drained the radiator using the drain plug so I could replace the coolant. I replaced the plug and filled the plastic coolant bottle. I started the engine and let it run for a few minutes. Only about 1/2 the bottle went into the engine. The oil on the engine started to smoke. Knowing it was overheating I shut it off. I filled the bottle, let it cool overnight and all of the coolant had gone into the engine. I filled the bottle again and started the engine. It seemed to be okay. I drove it for about 10 minutes and now the temperature light comes on and goes off while driving (no gauge). However, it doesn't appear to be overheating when I raise the hood and the bottle is staying 1/2 full. Do I have an air pocket that's causing this? Should I 'burp' it at an angle like I've seen discussed? Thanks!

From what I understand your supposed to fill the closed system at the thermostat . I have the same system 1990xj and this is what the radiator shop said. Just a bad system all the way around!! My heater stopped blowing hot air so I'm thinking clr to clean out my lines . I have a new Radiator and the hoses aren't collapsed . When I was sitting In traffic the other day it ran 210 I guess this normal ?

Assuming the air bleeder hole in your t-stat is at 12;00, you just fill it on level ground, or with the front up one foot. Run it till it warms up then let it cool. With it running, again fill till the expansion bottle is 1/2 full. (It NEEDS air in there, to compress). Then keep an eye on it, refill to 1/2 as needed the next day or two. 50/50 water/coolant. always.

Well the new engine does have more power, but didnt cure the overheating problem. So i was at a loss, and went to lowes and bought a t to t off the t stat housing. Put a mechanical gauge in, and routed it under the windshield wiper just to drive down the road. Well climbing a 6 % grade it never went over 200 degrees, while the stock gauge said it was getting hot. So on the plus side, my jeep is basically all new, but the problem was just a gauge. So dont trust your gauges i guess.

dang now im starting to wonder about mine when i go up hills it starts going near the 230 spot i have a ford electric fan and the stock aux fan both on and it still goes up i guess i will put a mechanical guage in an see what happens

how much did you find that used motor for? mine has 255k on it, runs good passes smog but i know it doesnt have all the power it should

Doing a water pump change any recommended for a 1990 xj 4.0 L? Automatic 2w. 4h. Part time 4. And 4low possible link/ or a video ? Thanks guys! Hop everybody's enjoying their Sunday !!

Doing a water pump change any recommended for a 1990 xj 4.0 L? Automatic 2w. 4h. Part time 4. And 4low possible link/ or a video ? Thanks guys! Hop everybody's enjoying their Sunday !!

I normally just trust Napa when I have the choice. I guess for just about anything except the T-Stat. (although I'm not sure if they sell the evil Airtex fuel pump or not)

Used engine had 150,xxx miles on it. I paid 250 bucks, but tore it down to check everything and replaced all the gaskets and seals.

Hopefully, it looks simple even without pulling the radiator. What's the recommended operating temp for 4.0 L? Pep boy auto, showed me two different water pumps. One had a different size pulley and the bolt size was different .

You don't need to pull rad. Just pull e fan out, and go for it. Also I. Dont trust anything pep boys sells. Go to Napa, o reillys, or even AutoZone. Buy a new pump not rebuilt.. and yours is a reverse rotation. Any more questions let us know.

for those suggesting the Tstat could be in backwards...? not sure on the older ones, but it can't be installed backwards on my 97.

also, not sure why a mechanical water temp gauge didnt make it's way into the equation early on. like first step in diagnoses.

Because it started over heating over night. And had replaced everything up to this point.

There's no way to install t stat backwards on a 4 liter. It won't fit.