2004 XJ8 with 4.2. I have a slight cooling system leak. There is no obvious leak. I used UV dye and the got a hit on the water pump. I replaced the radiator and water pump. System will still not pressurize with a tester. I am thinking the heater core or the aux heater pump. Never had a aux heater pump so don't have any experience with that. I assume the system should hold pressure? Agreed? Suggestions please.

 

God forbid it be a small leak in the valley hose. Did you look for a leak down back of the engine/trans? It's very hard to find, the dye will help. Most cars leaks are in the front area, heater hoses, as were you first checked. But ours also has a prone area we ALL don't want to find leaking.
I hope its not that.
Mark

 

I had a persistent coolant leak. It looked as if the radiator was leaking, so I changed with new hoses. But the leak persisted. A test showed I was burning coolant out the exhaust. Not good news - either intake or head gasket (quote $3800 to replace). Tried a $20 can of high quality sealant, which seems to have stopped the leak. So you might have your coolant system tested for leaking into the engine and then burning out the exhaust.

 

One suggestion I would offer is that I've found it is sometimes easier to see pinhole leaks using a flashlight in the dark. You can raise the front end of the car and remove the two undertrays, then either in a dark garage or outside at night, start the engine and use a flashlight to inspect every part of the cooling system from above and below, taking care to avoid getting too close to any moving parts. Pay special attention to the nest of hoses under the coolant reservoir/header tank and the small hoses that T off of the large radiator hoses, because coolant squirting from a pinhole in those areas can be quickly dissipated in the air flow of the radiator fan.

Cheers,

Don

 

Just a quick question: the valley hose is something only on the supercharged X350s, right? I'm trying to track down a coolant/vacuum leak and would like to cross off the possibilities.

Thanks.

 

Correct. The Valley hose applies to supercharged engines only. Stock XJ's will not have this issue.

 

Yes it's a closed system. You would have seen the Auxiliary heat pump in front of the right cylinder bank when you removed the radiator. Do a search if you need to. A leak there is easy to spot. The cap is 14.5 psi which is the max pressure in the system so you want to make sure you're not over pressurizing it and causing the leak.

 

As I have mentioned on another thread, watch out you're not losing coolant into your transmission.Not likely,but rule it out first as can be costly. First hint,in my case was the coolant looking sludge like.

 

What a minute...only XJRs have the leaking valley hose? I thought all the 4.2 V8s had this problem.

 

Thanks for all the advice. I removed the intake manifold and replaced the valley hose. The engine starts and idles fine but now I get a "RESTRICTED PERFORMANCE" message. Code P0117 coolant sensor. The temperature gauge will go HOT very quickly. Too quick, the engine hasn't had to time to get warm. I guess there must be air trapped in the system. I removed the bleeder plug when I filled it. I had the throttle body off maybe that has something to do with it.


Is there something special you have to do to bleed this?

Also the car will not shift out of 1st gear or speed up. I assume it has gone into some "LIMP HOME MODE". I am assuming (hoping) that once I get it bleed everything will run fine. What do you guys think?