I literally took the car for it's first drive since the two mile trip home last night, and the temperature started shooting up. It was in the normal range for about five-ten minutes. Naturally, I shut her off. I was able to limp home by coasting a long way then starting the engine only for a few seconds when necessary to get up a hill or go through a stop sign, then when the temp started shooting up again, immediately shutting it off again.

I'm guessing it's the thermostat, since the fan runs for a long time after the car is shut off and there is no issue with air conditioning, hoses, fluid leaks, etc. The coolant is topped up nicely.

Does this sound like a good diagnosis? And can somebody tell me how to get at the thermostat to replace it?

Sorry if this has been covered before. I looked through threads, and found a variety of information, but nothing specific to a '98 XJ8.

 

TSB from YEARS ago!!!!!

bob gauff

 

You rock! That is pure gold.

I saw a comment somebody else made about a ck ball that should be popped off when replacing a thermostat--does that apply for my car?

Oh, and what would be my best resource for affordable (but high quality) parts?

 

could also be a waterpump. The early cars have a plastic impeller that fails, there is a revised version to replace it. Try the forum sponsors for parts, you get discount for mentioning this forum, or Jaguar main agents.

 

Yeah, could be the waterpump. It's easier to do the waterpump and thermostat at the same time. It's really not hard. About all you need is the parts, a 1/4 inch drive ratchet and 8 mm and 10 mm sockets. The gaskets are all rubber rings, no gasket sealer. Don't scrimp on the thermostat and get a waterpump with a metal impellor. This is one of the must-do things when you get one of these cars, unless you KNOW it's already been done.

 

FORGET A METAL BLADE ON THE WATER PUMP. THE AFTERMARKET ONES IVE SEEN TEND TO HAVE SMALL IMPELLERS AND CAN LEAD TO CAVITATION. BUY A OEM FROM PARTSGEEK.COM THEYRE $140 FOR BOTH PUMP AND T STAT YOULL NEED THE PUMP GASKET TOO.98 1998 Jaguar XJ8 Thermostat - Cooling System - OE Aftermarket, Beck Arnley - PartsGeek
TO VERIFY IF THE WATER PUMP IS GOOD AND STILL HAS IMPELLERS WITHOUT TAKING IT OFF. ALL YOU DO IS TAKE OFF THE RESERVOIR CAP AND REV THE ENGINE. YOU SHOULD SEE COOLANT FLOWING IN THE RESERVOIR FROM THE BYPASS HOSE UP IN THE TOP OF THE RESERVOIR. IF NO FLOW YOU DONT HAVE IMPELLERS LEFT. THIS WAS ONLY AN ISSUE ON THE EARLY V8'S AND MOST ALL HAVE BEEN CHANGED. THE LATER IMPELLERS ARE MADE FROM A DIFFERANT AND MORE ROBUST PLASTIC AND IVE NEVER EVER SEEN REPLACEMENT COME APART SO DONT REPLACE IT JUST TO REPLACE. NOW ON THE T STAT REPLACE IT EVEN IF YOU FIND THE PUMP IS THE ISSUE. ANYTIME THE ENGINE OVERHEATS IT CAN DAMAGE THE CORRECT TEMP CONTROL OF THE T STAT SINCE IT IS A WAX BULB TYPE. AND YES IVE POPPED THE BRASS CHECK OFF THE TOP FOR YRS TO STOP COOLANT SURGING A VACUUM LOCKS THAT CAN SOEMTIMES CAUSE THE HOSE ON THE T STAT BARB TO SUCK OFF OR BLOW OFF AND IVE NEVER PULLED A T STAT IVE PULLED THE CHECK BALL OFF FOR OVERHEATING AGAIN
PEACE

 

Brutal, I assume (forgive my ignorance, I'm capable of wrenching, but have seldom worked on anything more complicated than an old '68 Mustang) should I be looking for a certain brand?

I'm on PartsGeek http://www.partsgeek.com/catalog/199...ater_pump.html but see no specifications for OEM; some say OE Aftermarket (which should be good, right?) and there is one water pump which says OES Genuine, which makes me think it might be the factory specified part, but I'm unclear on that. It says "OES Genuine" the same place that other brand names are located for other listings. Can you enlighten me? Sorry again for the stupid question.

Thanks for your help, everyone.

 

Oes is in a jaguar box(original equipment stock) at least everything ive ever gotten from them

 

Okay, hopefully my last silly question of the day: can I use any old antifreeze in the car or must I actually use the Jaguar branded sort?

 

I prefer jaguar coolant because it stains when there are coolant leaks and makes much easier to find over others that do not and i dont have to buy it. But you want to use a long life coolant either way. If in good shape save and reuse your original

 

Cool. I will endeavor to do that. Oh, and judging by your test, the water pump isn't working. When I rev the motor, the coolant just sits there.

 

And that would be why it overheated so fast too, even after a restart. Without the coolant circulation the engine overheats really quickly

 

You don't have to use the Jaguar branded coolant, but you have to use the correct type to match what is in your system already.

The later years shipped with a Dexcool type of coolant, but the earlier years shipped with both conventional green, and an intermediate type.

Look at the labeling on your reservoir, and then verify the actual contents visually. If there is a conflict then search for the VIN number breaks on this site.

 

Alright.

Indeed!

 

Sounds like the thermostat but let's hope it wasn't severely overheated before you purchased it. Exhaust gasses getting into the coolant via failed head gaskets can display the same symptoms. If the upper radiator hose is still hard after sitting overnight then you may want to test the coolant for exhaust gasses.

Usually there's alot of pressure when this happens (enough to push past the cap) so I wouldn't be overly alarmed. Its just something to check before dropping a few $100 in parts.

 

It's not.

 

Hi
I bought the metal thermostat housing at an online bidding website for about $40 and it did not include the thermostat. I do not recommend that online website - the vendor - I had problems getting him to accept the paypal payment that he had agreed to before the purchase.

I purchased my thermostat at Welsh Enterprises for $24.95 plus $7.85 shipping (total $32.80).

Welsh sells the updated water pump (AJ88912) for $69.95 and the metal thermostat housing kit with thermostat (AJ8-2217-KIT) for $65.95.
Total for water pump and thermostat kit with shipping ($11.48) would be $147.38.
Total for only water pump with shipping would be $73.80.

The updated water pump is $8 more at Gaudin Jaguar Parts online (pump is $73.13 plus $12.95 shipping (total $86.08). Metal thermostat housing kit is not available at Gaudin Jaguar.

Jim Lombardi

 

I just got my jag. and it seems to be overheating when Im in traffic. I see some coolant leaking from a plastic retention tank underneith the driver side headlights. I see some steam from the top I have not been underneith yet. All I've done is open the hood and I see the steam heating the engine from the plastic tank. But it only happens when I turn the engine off. It seems to start boiling and then the plastick tank starts to leak. Im thinking it may be the t-stat. I have good circulation from the thin hose comming to the resevore where you fill with water.... ANY IDEAS? I was thinking of changing the t-stat myself, Is it difficult?

 

Hi
I extracted this Thermostat removal & install instructions & illustrations from the JTIS21 Shop Repair Manual CD:

1998 XJ8 Thermostat R&I.pdf

This JPEG file is the illustration for removing the engine covers:


A quick way to drain the coolant is to removal the lower radiator hose at the bottom of the radiator. Put a pan to collect the coolant under the hose.

If you want to replace the plastic housing, here is the thermostat housing removal thread:
https://www.jaguarforums.com/forum/j...removal-56208/

It also has links to other threads that deal with replacing the thermostat and its components.

Jim Lombardi

 

Hello again
Look at this Coolant flush/fill thread on this forum:

https://www.jaguarforums.com/forum/j...sh-fill-52842/

Here are a lot of postings in the thread. The most recent ones cover air cleaner filter and other fluids.

Go down to posting #8 for cooling fluid information. Then read all the postings from #8 down to #1.

Jim Lombardi