Weird Cooling Issue havent read anyhting like this?

Ok so i have a issue with my cooling system, it all started last Saturday, i went out hunting and my temp gauge would jump up to a 100 then spike right down to 40 on and off all day, so i figured it was a sticking thermostat spent the night changing it found out the coolant was well overdue being changed so thought that also could have been the problem, But to no surprise i still am having issues and cant quite figure it out.

I had did a flush and changed the thermostat but now my enigne runs hot when the idle is low or im stopped at a light, for example i can be driveing down the road doing 60 k and its just above 40 where it should be then as soon as i push the brake for a stop sign or a light bam it jumps right to 100 until i start driving at regular speed again then it slowly creeps down, so i figured hmmm maybe i didnt quite (burp) it good enough and found out if i leave the cap off the bottle and let it run for even 10 seconds and shut the truck of the thing is like a volcano and burps like no tomorrow and this will keep doing it non stop, if i turn it on let it run shut it off does it again and dosnt stop so im not sure what to check next or what to try im stumped cant figure it out any ideas would be awesome don't want this thing running hot and if i can fix it would be awesome thanks in advance for any advice

Typical description for a failed/failing fan clutch.

NAPA 272310 is the 97-98 ZJ HD fan clutch, $44 down here, direct fit.

Also, buy a Stant 10244 pressure bottle cap, it will work better and gives a slightly higher boiling point to your coolant.

WOW I had to read that twice.....I was thinking Fahrenheit not Celsius. I had to look at your location then it clicked..lol

But yes I second what Joe has said.

Yes, it will boil out of the serge tank if the cover is of just like taking a cap of a radiator will, essentially the same idea.

Where you said it would spike I would check/replace your temp sensor for the gauge as well.

well joe i sure hope your right because that would be awesome if it was that easy im going to have to change that this week and have to get back anything else it might be? and with the pressure bottle should i jsut replace the cap? is that usually what fails is the cap and not the tank threads?

so would the fan clutch also make it burp with the cap off every time i shut the engine off?

That would be a issue with your cap not holding pressure.

well it does leak out of the cap when she gets warm but i mean if i take the cap off the tank start the truck it runs gets hot then i shut it off then it starts burping like crazy then ittl stop after like 30 seconds then if i was to leave the cap off and start it again run it for a bit then shut it off burps like crazy again? and will continue to do soo evey time i shut it off with the cap still of so thats what im stumped about

CromeY90 said:

well joe i sure hope your right because that would be awesome if it was that easy im going to have to change that this week and have to get back anything else it might be? and with the pressure bottle should i jsut replace the cap? is that usually what fails is the cap and not the tank threads?

Click to expand...

Yeah. Some have tried using screw clamps--tighten down the cap to just short of "popping" loose, then put a screw clamp around it and tighten down. The Stant cap works much better, it has a lower profile so the underside of the hood isn't impacting it and causing stress cracks in the pressure bottle--check the marks on the underside of the hood over the cap--and the higher pressure rating is good too.

The bottle should be 1/3 full when cold. The rest of the space is for the expanded coolant.

Once repairs have been made make sure to burp the system--park it with a nose down attitude, then remove the temperature gauge/idiot light sending unit from the rear of the head, then just add coolant to the pressure bottle until all air is forced out at the sender port. Do be careful with the sending unit, they break if you aren't reasonably careful with them.

Good luck.

ok so i changed the fan clutch tonight and got my aux fan running finally stupid relay but still only comes on when its on defrost. So after changing the fan clutch still runs hot and a weird thing i noticed is when im driving as soon as i push the brakes and the nose drops down the temp goes up, and after the truck levels out its slowly goes back down but is still running hot when idling but when driving normally runs at perfect temperature. I found that when i took my cap off the pressure bottle that the gasket on the cap was so swollen that it was pushing its self out of the grove could this be part of the problem that the cap isnt sealing properly? could the cap reek this much havoc? any other options or opinions what this might be would be awesome. Also another thing is that my upper rad hoes feels like there is no coolant in it feels empty when i squeeze it is that normal as well?

and another question whats the usual normal running temperature of a 90 ish xj when everything is working properly??

btt

210-ish would be normal, normal ambient temperature, normal load on the engine.

Mine runs about 205 with the ZJ HD fan clutch no matter what I'm doing.

Without pressure your coolant will boil at a lower temperature, the system is designed to work at pressure--other wise you could just put plastic wrap over the bottle and secure it with a rubber band to keep dirt and bugs out.

Please read this article and it will be abundantly clear how pressure helps your system:

http://auto.howstuffworks.com/cooling-system3.htm

so i read that and its not really clear just says you need pressure to raise the boiling point, so because the gasket on my cap is fugged the water is getting hotter quicker because the pressure is leaking out so there fore makieng the engine run hotter? am i correct?

Without the pressure your coolant will boil 40-45 degrees F SOONER than with the correct pressure on the system.

A 50/50 mix will BOIL at 106 degrees C WITHOUT pressure, or you can raise the boiling point 25 degrees C just by adding PRESSURE.

That a little clearer?

so my cap seal being broken could be the reason im having all these issues because i changed the fan clutch and its still doing it so i guess ill be ordering a new cap tommorow hope that works

Yes. Get the Stant 10244 cap from Napa for about $8. Start there. And, the temp sensor for your electric fan may be bad and not triggering the fan to come on at the proper temp. The reason it comes on with defrost is it's designed to do so.

Here is a great fix to this problem, I myself have a 89 XJ and I could never find a cap that would last holding the pressure in the bottle. Being that the bottle is made in Spain? or some other foreign country the threads are metric. I also owned a Volvo 240 turbo a long time ago. I simply switched the caps to see what would happen. The Volvo cap screwed on tightly and held pressure and has been on my XJ ever since. We are talking 7 or 8 years.

JUst scour the wrecking yards for a Volvo Turbo, either a 240, 740 or 940 turbo. The cap that you want is green in color which is designed to handle the higher temps associated with a turbo motor. They also have a black cap available which would be more readily available but not sure it will handle the pressure. Get the green cap to be sure.
Hope this helps

One thing to remember is that 100c is normal operating temp, if you are having other issues such as leaks, fix those... but at 100c you are not overheating. Also, 40c is quite low. I'm guessing you live in a cold climate?

CromeY90 said:

ok so i changed the fan clutch tonight and got my aux fan running finally stupid relay but still only comes on when its on defrost. So after changing the fan clutch still runs hot and a weird thing i noticed is when im driving as soon as i push the brakes and the nose drops down the temp goes up, and after the truck levels out its slowly goes back down but is still running hot when idling but when driving normally runs at perfect temperature. I found that when i took my cap off the pressure bottle that the gasket on the cap was so swollen that it was pushing its self out of the grove could this be part of the problem that the cap isnt sealing properly? could the cap reek this much havoc? any other options or opinions what this might be would be awesome. Also another thing is that my upper rad hoes feels like there is no coolant in it feels empty when i squeeze it is that normal as well?

Click to expand...

That sounds like air in the system...

ok so i finally got some time to tear into this fu#%ing problem got the stant 10244 cap very easily and only for 14 bucks, so i threw that on and still having the weird issues, so i got home and for some reason wanted to drain the pressure bottle and decided to clean it, so i drained it and found a surprise the bottom hoes was so freaking clogged with what i believe was bars leak barely any water would flow threw it, i mean i had to use a coat hanger to d clog it and 10 minutes later was free and flowed good so i let the engine sit in the drive way for a while as i was cleaning and the temp was hovering just under 100C and tried the aux fan threw it on defrost and the temp moved to about half way between 40 and 100 so im hoping this is the fix i was looking for and ill keep you guys posted as ill be doing alot of driving this weekend thanks to everyone who helped me hopefully fix this dang problem cheers