Like the title says, I have a 2004 S Type with the 4.2L V8. Had a local shop replace the knock sensors. Now I have a mysterious coolant leak. I've added dye and looked all over, but no evidence of a leak. Looking for possibilities, any of you gurus have a suggestion?

Thanks,

Brian Smith
NW Louisiana

 

Well, which is it? You've kinda contradicted yourself. Perhaps you could define "coolant leak". Are you seeing a puddle collect under the car, smelling hot coolant, or something like that?

Or do you mean the coolant level in the reservoir keeps dropping? That is somewhat normal for a little while after the system is disturbed, no matter how carefully you bleed it.

 

Good point. I do smell a hint of hot coolant and the level in the tank has dropped a lot (ie I've added a whole gallon of coolant since the repair.

 

Putting on my Sherlock Holmes cap, and lighting my Sherlock Holmes pipe:

How much have you driven the car since the repair? And was the shop familiar with the elaborate bleeding procedure for the cooling system? I've attempted it myself, but gave up after the part about sacrificing a chicken while chanting a Latin incantation.

I wonder if this scenario occured: The shop replaced the sensors, but spilled some coolant in the process. The coolant likely collected in the bottom of the intake valley or some other inaccessible spot. Then they topped off the coolant, unaware of the bleeding procedure. You drive home and smelled the spilled coolant as it heated up, and noted the low coolant at the reservoir.

If you haven't driven much, that spilled coolant hasn't had much chance to burn off. For peace of mind, I'd do a cooling system pressure test. This is the doohickey, similar to a bicycle pump, that connects in place of the reservoir cap. Pump up the system to the rated value on the cap. Let it sit for 15 minutes. You should not see any notable pressure drop in that time.

If you have a leak, you'll see a noticeable pressure drop. Just running the engine and looking around at idle will miss most leaks. There's not much pressure at idle. A pressure tester is the way to go. If you don't want to purchase one, many parts stores loan them for free.

 

My wife drove it to work a couple of times (about 50 miles round trip and Interstate speeds). I checked when she returned, coolant drop in reservoir.
Pretty sure the shop isn't familiar with the specific "Jaguar" procedure involved, but they are an experienced shop with other vehicles both foreign and domestic.
I have not done a pressure test, but will.
I did the UV look immediately after the car returned from my wife's commute (ie, car was hot and cooling system under pressure), still no sign of leak.

 

+1 on pressure testing the cooling system after a cold soak, preferably overnight. Pressurise the system to 1 bar for at least 10 minutes and if the pressure begins to drop, look for leaks. The EGR feed hoses are something that should be replaced if the inlet manifold is removed as they can fail and leave you stranded.

The normally aspirated cars should also have the water outlet assembly replaced whenever the coolant is changed as it can only withstand a finite number of cold to hot to cold cycles before failing. The part number is AJ811793.

 

They might have disturbed or damaged the valley hose. Its in close proximity to the knock sensors underneath the intake manifold.

 

Look at the situation this way:

If the pressure test fails, even if you can’t see a leak, it’s the shop’s problem, not yours. They caused it and will have to fix it on their dime.

If the pressure test passes, and the coolant refills taper off, then there’s no leak.

You win either way.

 

Ive never known a shop to admit they screwed up. They'll claim its a separate issue that just popped up.

 

Dear listers

I finally got around to renting a pressure tester. Engine cold, Pressued the system up to 20 psi (the pressure listed on the cap). In 15 mins, pressure dropped about 2 -5 psi. Checked again, very slow pressure drop, noticed that the coolant tank was low. Topped off coolant and ran test again. noticed not only pressure drop but small coolant level drop. So, figure I'll take it back to the shop that did the original work.

 

Yep, sounds like you've got a leak. Keep us posted and let us know what the shop has to say.