Hello all, I've been lurking on this forum for a while, trying to learn a thing or two about X300s before taking the plunge. Well, this past week I bought a 95 XJR, 144K miles, needs some minor sorting but in pretty good shape overall. I've always done most of my own car repairs, including fairly major ones, so I'm not afraid to tackle most repairs on this car. In a nutshell, I've got a coolant leak from somewhere on the driver's side of the engine that I can't easily locate the source of. I'd appreciate any wisdom on the likely source of the leak so I can avoid taking apart more than I have to in order to fix it. Details of the problem are as follows:

Yesterday morning, I started it up and began to back out of my driveway, when I noticed a fairly small (maybe 15-20 sq. in.) puddle of coolant in the driveway. I looked under the car and could see a slow drip of coolant coming off the back of the front crossmember, just in front of the steering rack, toward the driver's side. Since it didn't appear to be any kind of high-volume/high-pressure leak, and since I was only planning on driving a short distance to my father's house, I checked the coolant level in the header tank, which was slightly above max (and no bubbles in the tank) and went for a drive. During the drive, the temp gauge came up to just below the "N" mark at a normal rate and did not go any higher.

While parked at my dad's for about 2.5 hours, the car continually dripped coolant from the same spot on the crossmember, as well as dripping for a short time from a small (maybe 1" diameter) protruding spot toward the front of the oil pan toward the driver's side. The drips were falling at a rate of one every couple of seconds. When I left, I checked the header tank again after starting the car and letting it run a little--the level had dropped below the max mark, but was still well above the min mark. I made a couple stops on the way home, and the drip rate stayed fairly constant.

When I got the car home, I put it up on ramps and poked around underneath and from above to see if I could determine the source of the leak. Again, all I could see was coolant dripping off the same spot on the back edge of the front crossmember, toward the driver's side. There was no longer any coolant dripping from near the front of the oil pan on the driver's side, just some green residue from the antifreeze. Interestingly, after letting the car cool for a couple of hours, the dripping stopped this time (recall that it had not stopped at my dad's). So I got back under the car, wiped the oil pan, crossmember and steering rack down so I could (hopefully) better trace the path of the coolant. Shining my flashlight around, what I could see of the lower radiator hose appeared clean and dry. In fact, I could not see any wet spots anywhere. So I started the car back up and after a couple of minutes, I could see antifreeze starting to collect on the "flange" (for lack of a better word) at the bottom of the block, where the oil pan bolts up. From front to back on the engine, this was in the general vicinity of the bracket for the driver's side engine mount. As far as I can tell, from there, the coolant runs down onto the crossmember, and ultimately drips off the crossmember a little further back, by the steering rack. But I can't tell where it's running down from in the first place. Looking at diagrams of the engine block and cooling system, and relating them to the location of the coolant on the bottom of the engine block, it seems feasible that the leak could be coming from the water rail. Due to all the intake plumbing on the XJR, however, I cannot even begin to get a good look at the rail to see if there is any seepage. I'd rather not take everything apart to get in there if I don't have to, so I wonder if there is another, more likely source?

A known issue which may or may not be relevant to my question: a rattle from the front end of the engine, which I have not definitively narrowed down yet. I believe the upper tensioner needs replacing, as there is a brief, but louder, rattle when the car is first started but that goes away within a second or two. There is a constant, lighter rattle however, which I believe is either the supercharger coupler or the water pump. I haven't removed the supercharger belt yet (I will do so today, time permitting), but I do not see or feel any coolant leaking from the water pump weep hole.

Sorry for the very long description of the problem, but I figure many requests for help don't include enough relevant information. Any and all pointers are greatly appreciated. I suppose I could just bite the bullet and tear it way down, doing the lower radiator hose, the pump-to-rail hose, the rail gaskets, etc., but I was hoping to wait until the car was in storage for the winter before doing work that extensive.

Thanks in advance,

Scott

 

Things would be a whole lot easier if it was the NA car. The supercharged model makes finding such problems that bit harder. There are a while lot of areas where it might be coming from. I wonder if it would be best just to take it to a garage and have them find the source of the leak with their flourescent dye stuff. There may be more than one leak?
If you want to have a go yourself, taking the fan pack out and supercharger belt off will increase access. Waterpump, octopus hose, and any union from rubber hose to alloy (where the alloy corrodes) can present leaks. A

 

Not sure if this will help but I had a mystery coolant leak on my XJR. In my case it was the gasket where the thermostat housing bolts to the head. It was leaking at the bottom...drip drip...where I couldn't easily see it. But, as you've noticed, there are other hidden possibilities. You may have to do some disassembly to find the leak....although I know you'd rather avoid it, of course.

Have you read up on the lower radiator hose...the "octopus hose" ? If you end up having to do some teardown to find the leak there may be a good opportunity to get the ugly job of octopus hose replacement out of the way.

There is a hydraulic chain tensioner that can get weak with age. It's replaceable from the outside of the engine. Never done it...but others here will comment and add some pics. I'll likely have to face the job myself one day. I guess it's pretty easy.


FTR, unless yours is a very early '95 the temp guage is a little deceiving. It will stay "just below the N" over a wide range of engine temperatures (starting at 174ºF) and then go higher after a certain threshold is reached. Not sure what that point is, but it's higher than 205ºF....as my coolant temp has been that high (reading from my scan tool) with the needle still one tick below the "N".

Cheers
DD

 

Thanks for the pointers. I am aware of the octopus hose and that was my first thought when I saw the drip, but what parts of the hose I can see (and granted, there are many parts I cannot) appear clean and dry. If I have to tear it way down, I figure I will replace all of the difficult to reach hoses, including the octopus, and the water pump as preventive measures.

Doug, I will check the thermostat housing, though I think that is probably a little far forward of where the coolant is running down. But who knows what other parts might divert the coolant once it starts running down.

Unfortunately, with all of the supercharger plumbing, a flashlight does not do much good from the top of the engine. I have an idea, consisting mainly of attaching a cotton swap to the end of a thin probe to help me "feel" around for the source of the leak in there. We'll see if that gets me anywhere. Otherwise, I'm probably going to have to start taking things apart.

 

Well, Doug, you may be onto something with the thermostat housing. Got back under the car with a better flashlight. Discovered that the crossmember drip was slower--maybe once every 10 seconds, give or take. There was also a really slow drip (maybe once every ten minutes) from the little protrusion at the front of the oil sump. I started the car up again and let it warm up, which increased the frequency of the drip by the rear crossmember. Shut it back down, got underneath the car, and with the better flashlight, I could see some coolant collecting on the front of the block underneath the water pump housing. The way I see it, with the car on an incline from being up on ramps, the only way coolant could end up on the front of the block is if it is leaking from somewhere way up front--like the water pump or thermostat housing. At the same time, it would be feasible that coolant would run toward the back of the engine, since it's on an incline. I took off the cover over the fuel rail and injector harness to get a better look at the back side of the thermostat housing. It looks like there may be some moisture down there, but nothing in the quantity that is dripping on the ground. So I'm thinking it's either leaking off the front side of the thermostat-housing-to-cylinder head joint, or the water pump is leaking somewhere, even though it appears to be dry up top.

Thanks again for your help. Once I've fixed it, I'll let you know what it was. Incidentally, how hard was it to remove the thermostat housing--it looks like the bracket for the supercharger idler pulley might have to be removed?

 

I needlessly replaced my water pump because of that thermo housing leak :-). Oh well....

I can't remember anything about removing the thermostat housing so it must not have been very difficult. You're obviously experienced....I'm sure it'll be intuitive once you start.

One tip.....

If you do anything involving the drive belts you'll surely find the adjuster mechanisms. ....a long bolt with a 1/4" square drive at the end. Each adjuster moves a pulley on a slide to actually change the belt tension. The center bolt of the pulley must be slackened for the adjuster to operate.

Cheers
DD

 

Doug, you are the man! It was the thermostat housing, and although it was a bit of a bear to work on in the 95 degree heat, it sure beats doing the water pump or the octopus hose! I'm still not sure precisely where it was leaking from the housing, but I cleaned up all of the sealing surfaces, coated everything with Hylomar, put it all back together and...no more drips!

Not sure if this was a contributing factor, but when I pulled the thermostat cover off, the thermostat itself was pretty mangled-looking. The "top" of the thermostat (the side that faces the front of the car) had actually broken on one side, causing the innards to get all cockeyed. My assumption is that the thermostat could neither open nor close all the way, and may have been causing excess turbulence or pressure in the thermostat housing due to the way it was cocked in there.

So thanks for the tip and if you're ever in the Detroit area, I definitely owe you a pint or two!

Cheers,

Scott

 

Glad it worked out for you. :-)

Cheers
DD