When I have ran my XJ for 30 to 40 minutes and then remove the Radiator cap, should there be pressure built up? When I remove the cap, I don't get any pressure relief at all....could this also be the reason I get very little heat and the temp guage won't reach norm any more?

 

bump

 

I would think no pressure would indicate a bad rad cap. Is the rad completely full (coolant present in the neck when cap is removed)? Low coolant temp is probably due to a bad t-stat (stuck open).

 

Thanks djb

 

Did you replace the cap yet? Mine is doing the no pressure thing as well. I'm thinking its one of the plastic tanks on the cheapy Rad though.

 

If your cap is lifting early your exspansion tank is going to be full unless it is drawing the liquid back in after it cools down. Run it at idle and see if you get any fluid back to the overflow tank.
The temp only has to drop below 212 degrees and you will not have any pressure. I can remove my cap after about 10 minutes and have no pressure on it.

 

better stuck open then closed

 

Not really, as the cooling system is designed to be pressurized. Without pressure, hot spots will form in the block and head where coolant will boil and vaporize........not good. We're talking about the rad cap stuck open, not the t-stat.

 

Mine never really gets above 210 regardless if I'm driving or sitting in traffic. Granted it's around 15* here, but I also have the mechanical fan off for the winter. I can go out after 30 mins. of driving and there is no pressure in the hoses. Just replaced the cap w/a OEM one. The overflow tank isn't overly full. I would say it goes up about an inch from when it's cold. I'm assuming there's a leak somewhere since it's not building pressure, correct?

 

I did also notice that on the OEM cap that I got the return valve is loose and just flops around and is not held shut w/a spring like the older style caps. I even went back into the dealership and checked it against another one on the shelf. I'm wondering if w/this valve hanging loose it's allowing coolant to slowly go into the overflow and not build pressure. That's why the overflow tank goes up a inch or soo and then goes down when cooling, but isn't building pressure. I remember on my '01 when I did a CSF 3 core and a OEM cap it held pressure, but I can't remember if it had a spring holding the return valve shut or not. Just a theory... What do you guys think?

 

Nothing loose on the new Stant rad cap we just installed........loose just doesn't sound right.

 

Ill have to take a pic of it. The valve just hangs. It isn't nice and tucked up against the rubber like it should be. Yours has a spring on it, so you can pull it down an it'll retract back right?

 

Yes.

 

Well, I went to AZ and picked up a different rad cap. The cap they handed me was the same loose valve. I found one on the shelf w/a spring in the return valve and Viola! Pressure in the hoses again. I did find now that the cheapy rad is leaking at the tank some.. Time for a CSF. I don't really get the concept of the newer caps w/out the return spring. I suppose if the fluid was flowing fast enough and had enough pressure to keep the valve closed, but eventually the pressure would even out and it would let coolant freely flow into the overflow tank. Makes no sense, unless they wanted to have little pressure in the system...