wicked 90 xj

First off, I drive a 1990 xj, 4.0L l6. My promblem is that when i sit at a red light for about ten minutes, it starts to overheat. Now, it has never got above about 230, it normally runs between 190 and 210. My fan works and i have an electric fan, when im at a red light i just flip the electric fan on and it wont get above 200. I have a new water pump, new oil pump all new belts, all new hoses, new t-stat. Oh, oil is clean and new head gasket. Basically everything under the hood is new, nothing leaks. The only thing that is not new is the filler bottle and cap. I read about some overheating problems coming from bad caps or bottles. I've checked the bottle, no craks or leaks. When I had the filler bottle cap off i checked the anti freeze, proper level. But I did notice for the next three days that i drove it, the truck didn't get above 190, even in traffic, like normal. after that, it started getting hot again. So that night i toke the cap off again when the truck was cool, put it back on, overheat problem gone for another two days, then started again. Now i know this is a closed system, so what i'm asking is, does anyone know what i should do? Does anyone else think the cap could be bad? Sorry for writing a book here, this is just starting to get under my skin! I want to fix it!

mudderx

My '98 does that when Im wheelin, I learned to back blast the radiator with a water hose after every trip and have not had any more problems. BUT if your cap is bad your cooling system will not work right,when the water is hot it expands filling you overflow tank,when it cools it sucks the water back into the radiator. If your cap is bad you'll lose the pressure in the cooling system causing it to fail...

rich

You didnt say you had a new clutch fan on the xj,if it is bad it wont work at low rpms like it should, thus not cooling at a stop etc.

89stroker

upgrade to a 3 row from a 97+ without the burp tank and put a 160 stat in it. will never get over 200

damageincracing

I have a 1990 as well, and had the overheating issue. Same thing, new radiator, t-stat, water pump, hoses... What I found is the cap on the pressure bottle will "stretch" at the bottom. Look at a brand new one from the side and it will be a nice even squared off shape, one that's been through a few heat cycles will bow out a little at the bottom. I saw this and threw on a new cap. 4 new caps in 3 months later, I made my own "fix". I got a hose clamp and put it around the bottom of the cap, then tightened it down just enough to "square up" the cap. Hasn't overheated since. Runs at roughly 160-180 all the time unless I run the a/c, then it does creep up until I kick the electric fan on (I wired mine through a switch- bad diode pack). If you need a pic let me know...

wicked 90 xj

Yeah, if you could post a pic that would be great. I think this is what im going to do though. I talked to a friend of mine and he said to do the same thing.

damageincracing

Sure thing. I'll snap one and get it up as soon as I can. Might take a day or two since the wife has commandeered the Jeep so she can get through the road construction on her way to work. LOL

wicked 90 xj

Cool, thanks.

damageincracing

Basically, take a hose clamp that's a little bigger than the cap, and put it on so the bottom edge of the clamp is flush with the bottom edge of the cap and tighten it just a little. All you want to do is "square up" the cap again. If it's too tight it will build up too much pressure in the system and bad things will happen... It took me a couple tries to get the cap to "feel" right when I screwed it on, but I haven't had the overheat problem since. One more little bit of advice: if the bottle is empty due to it overheating, fill it to about an inch above the bottom, then start the engine. The coolant will suck down and you will need to add more. ONLY ADD ENOUGH TO GET COOLANT TO FLOW STEADY OUT OF THE TOPMOST "BLEED HOSE" ON THE BOTTLE (closest to the fill neck)! Only fill it about an inch over the bottom of the tank with the engine cold (learned from experience). Then just keep an eye on it for a few days to make sure the air is bled out of the system. When mine is cold, it's only about an inch from the bottom, but when it's hot, it's up is the "full range" on the little dowel that sticks up in the bottle.