When I purchased my 2004 VDP at 140,000 miles it had a slight engine coolant leak. I replaced the water pump, which seemed to be leaking, but the coolant level continued to go low. Then I noticed a crack in the thermostat assembly that was leaking coolant so I purchased an off brand replacement that included new thermostat and engine coolant temp sensor. Replacement went fine, but after a couple drives the new thermostat appeared to be malfunctioning by not opening and not allowing coolant to circulate (the coolant level also kept going low). I put the old thermostat back in, and it worked, while the place where I bought the bad unit sent me a new one. However, the second new unit had the same problem (no circulation out of the radiator to the engine). Check engine light also came on with a P0128 code. In the meantime, the place I bought the bad thermostat assembly said their unit was wrong for my VIN. So now I'm waiting on a "real" thermostat assembly part from a Jag dealer. But I don't know if putting on the OEM part will solve both the overheating and low coolant problems. What could the cause(s) be?
-bad thermostat?
-plugged radiator?
-bad coolant sensor?
-wrong thermostat assembly (even though it seemed to fit)?
-something else I'm not aware of?

My next step is to put the genuine Jag thermostat assembly on and see if both the overheating/non-circulation problem and the low coolant problem persist. It's been puzzling, and I don't know if I'm on the right track. Any ideas?

 

I forgot to mention an important piece of information, that after the second thermostat seemed to fail, I put the old apparently functioning thermostat back on for a second time. The coolant seemed to circulate correctly on my first test drive, but then on the second drive the coolant didn't circulate again, leaving me to wonder whether the thermostat was even the problem.

 

If you have the 4.2L V8 they notoriously leak coolant from 1. the over flow nipple on the recovery tank 2. the plastic thermostat housing 3. the two coolant hoses that go under the intake manifold to the heater core.

 

Thanks. I'll take a closer look at those.

 

Overflow tank on my 2004 XJR was replaced early when the car had only 20K miles on it. So its very likely an area of concern
RyeJag

 

I haven't noticed any leakage there, but I suppose it's possible there's some leak point I can't see that is diverting coolant in a way that looks as if it must be coming from somewhere else.

Any ideas on what could be causing the overheating problem?

 

Issues resolved. I thought there might be a leak coming from my 3 month old AC Delco water pump, and sure enough the plastic impeller inside was chewed up. So I put in a new one which resolved my slow coolant leak and my overheating problem. I has passed on considering the problem being the water pump because it had just been replaced. Pleased to have all that resolved!

If you're interested, I had two more challenges. First, my windshield washer pump stopped working. I had voltage to the connector on the pump, so I was advised the pump had just seized up. I bought a universal pump for under $20 (as opposed to an OEM replacement pump for $300+), installed it, and my cleaner fluid's flowing again.

Second, no sooner had I closed the hood on the washer pump fix than the hood stuck closed. I read horror stories about drilling 1" holes in the wheel well to get at the opening mechanisms. It took a couple days of going back to the car and checking everything out, but I finally figured out the opening mechanisms could be reached through the front grill. The passenger's side one popped pretty easily by inserting a long screwdriver through the grill and sideswiping the gear. The driver's side gear was covered by the electronic apparatus that indicates whether the hood is correctly closed, so I couldn't reach it through the front. I took off two plastic protectors under the front end so that I could reach up from underneath in front of the radiator and sprang the gear that way. I used penetrating oil and lube oil then to make sure the spring mechanisms would work freely, and it's working right again. I was prepared to take it to a body shop tomorrow to see what they could do, but a little persistence and some reasoning saw me through.

 

Just a couple of quick questions. Did you replace just the thermostat housing, or the complete thermostat housing tower? If the tower, how easy/hard was it to take off? Did you have to remove the throttle body or the intake manifold? Was the replacement plastic or metal? My tower has a hairline crack (which I epoxied while I order the replacement and assortment of hoses, etc. (going to replace all hoses while I'm at it--understand I have to take the intake manifold off for one of the hoses).

Thanks in advance.

Gordon

 

Hi Gordon. Good questions and ones I encountered at the start or along the way.

I replaced the entire (plastic) thermostat housing assembly because I had a hairline crack too that was leaking coolant. Similar to you, I used JBWeld as a temporary fix. I found it easiest to remove the throttle body and then start removing bolts from the thermo assembly, working my way logically down to where the final pipe entered at the intake manifold.

That was the hardest part because some bolt heads are hard to get at. But patience, persistence and a variety of tools did the job for me. Because of the tight space, the two farthest back bottom two bolts of the thermo pipe entering the intake manifold were hardest to get off. Not having a small enough open ended wrench I started them off with a socket but then ran out of turning room and finished with a needle nosed pliers.

This final pipe that I'm talking about inserts into the rest of the thermostat housing, sealed not by any bolts but just by being tightly fitted against an O-ring. You'll be able to see what I mean and take it on and off your replacement assembly before installation. It might be possible to leave the old one on if it's too hard to get at and the replacement unit fits it. But while I was there I chose to do the somewhat painstaking work of replacing it (after all, it could fail down the road too). Ironically, since my water pump was bad without my knowing it, I thought I had gotten a bad new thermostat and had a replacement sent. Then I even ended up going with a different manufacturer, so all in all I replaced the whole thermostat assembly twice before I figured out the issue of my coolant not circulating was not the thermostat but the water pump. Go figure.

My hoses looked fine, but that's a good idea to be proactive in replacing yours while you have things torn apart. I hope that's helpful. Wish I had pics for you. Feel free to ask if you have more questions.

 

kbeachy
thanks for the detailed info. The water pump you are referring to is the circulating pump for the heat? where is it located? What model engine do you have? supercharged or not?
RyeJag

 

Hi RyeJag,

The water pump is what circulates water from the radiator through the engine and is also responsible for hot water circulating through the heater core. I have the 4.2L aspirated (not supercharged) V8 engine. The water pump is located below the top coolant hoses and is the topmost apparatus run by the serpentine belt. It's kind of hidden until you look down through the openings in the hoses, but when you locate the path of the serpentine belt the water pump pulley (attached to the water pump itself) is at the top of the path of the serpentine belt. Hope that helps.

 

kbeachy, thanks for the info.

I haven't been able to find the hoses that connect to the throttle body (I got all of the other hoses (except the one that runs under the intake manifold) from Autopartswarehouse). I also got the thermostat housing tower. However, they don't come with any gaskets, etc., so I'm afraid I'll have to go to the dealer for them (yuck).

When you changed the water pump, did you need a "special" tool to remove the belt pulley from the water pump? I ordered one as well (figured I might as well just replace everything I can get to). Thanks,

Gordon

 

Hi Gordon. Funny you should mention autopartswarehouse. I bought my thermostat housing assembly from them (it did come with gaskets and O-rings). While it seemed to be just like the OEM, they ended up telling me it wasn't the right part for my VIN and gave me my money back. I wasn't very impressed with their expertise and customer service, but prices are great (their markup was so small--only several dollars on a $60 part).

Here's a link to a Jaguar dealer who also sells online with reasonable prices: Jaguar Parts Center - Call (800) 510-1401 for Genuine Jaguar Parts and Accessories. I got my thermostat housing assembly then from them. I also suggest you change your serpentine belt while you have it off. But either take careful note of the belt path or print off a diagram from an internet search because it's awfully tricky getting it back on (it usually takes me about 10 minutes even with the diagram in front of me).

The water pump's belt pulley is attached with 3 bolts that come off with (I think) an 8mm socket. Just make sure you loosen (not completely remove) the bolts BEFORE taking off the belt because the belt provides enough tension on the otherwise free turning pulley to turn them loose. Once I forgot to do that and then had to attach a vice grip to the edge of the pulley to hold it in place while I loosened the bolts. Likewise, wait to fully tighten the bolts down until AFTER you have the belt back on when reinstalling.

I've also had good service and parts at RockAuto Parts Catalog. Let me know how your project goes. Good luck!

Kenton

 

They asked me for my VIN (I ended up purchasing from APW over the phone although they did select the same parts I did with one exception). I went to Rock Auto first, but they had very little in the way of hoses for the X350.

Great advise!!!

 

Thanks for the link. APW ended up not having two hoses (to the recovery tank), so I am going through that link to find what I'm missing.

Two questions:
1. On the rear of the thermostat housing tower (directly behind where the thermostat is and facing the engine, what is it connected to and how is it connected/sealed? I can't really see looking at it what it "connects" to or how it seals. The other ends all have O rings, so I'm not worried about them. But this has nothing, so I can't tell if it how does that. It is where the arrow is pointing to on the tower (picture from rear (from engine looking forward).

Also, the second picture is an "inlet" part that came with the housing tower, but I have no idea where it goes or what it attaches to. There's no place on the tower that it connects to. It does have an O ring so if I can figure out where it goes, then I'm set on seals, etc. on the one side (the other side may need something).

Anyway, any and all suggestions are greatly appreciated. I'm trying to get all the hoses, parts, etc. so I can do all this stuff during the week of the 4th.

Thanks,

 

Surely the rear of the housing doesn't connect to anything, it's just the bottom of the housing.

 

I wish! But no such luck.

Looking into the rear of the housing opening in the first picture, you can just make out the edge of the thermostat. In the second picture, you can see light where a hose gets connected, and in the third picture, you can see where that hose connects.

So, the rear needs to seal/connect with something. It looks like there is something that is a smaller diameter that it goes over, but I can't tell what (probably won't know until I can pull the throttle body, etc.). I just don't want to pull everything apart and then realize I'm missing a seal or something.

Ideas?

 

Sorry it has taken me so long to reply but just got back from a several day vacation to Niagara Falls where I disregarded anything internet related.

I hope I can answer your questions. The two pieces of your thermostat assembly fit together. The rounded end of the pipe-like piece that has an O-ring on it fits snugly inside the back end of the other part (where the arrow points in your first picture). The O-ring makes the seal against the inside of the other piece. So the pipe-like piece will actually be able to rotate once it is snuggled inside the other piece. That allows the very bottom end of the pipe-like piece with the four bolts to fit over the engine where the water will flow out of the thermostat assembly and into the engine.

When you start taking the old thermostat assembly off you'll be able to see better how everything fits. You have all the parts/pieces you need. It's the bottom most piece that causes you to have to take the intake manifold off in order to get to the four bolts. Being a DIY type of mechanic who learns as he goes, I'm not very good at names of parts, so I hope what I've described is understandable. I'll be glad to answer any questions as you proceed!

 

That's super helpful! Thanks.

So, any particular reason why I should replace the bottom piece with the four bolts if there is nothing wrong with it (so I don't have to take the intake manifold off)? Of course, I'm answering it in my mind as I write this: It's plastic and it's hot in there. If the other piece cracked, this piece is probably on its way out and I don't want to do it twice.....

Dang it! I did not want to take the intake manifold off; I don't have a new intake manifold gasket and am leary of using the old one in case it doesn't seal properly and I end up with an air leak. Oh well, that's what you get (doing all that work) for piece of mind.......

 

Hi Gordon. I think you answered your own question with what my response would have been. If you can tackle the job I'd say it's worthwhile replacing the part because it could fail down the road. Easier now than possibly later.

If I recall correctly there is no gasket but another O-ring on the intake manifold. I re-used what was there already and haven't had any problem. In order to move the manifold away from the engine block it's necessary to take another part off that's attached to it. I don't know the name of it but it's probably a vacuum hose or tube of some kind that runs to this part. It should be evident to you what else you have to take apart once you're there.