Can someone please help me troubleshoot before I go in the wrong direction? I've got a 1999 XK8, the top radiator hose is suddenly hot, soft, and certainly about to fail, the bottom hose is always cold. My wife drives the car 1 hour each way to work, the other day was 5 degrees, and the heater stopped working on the way into work. The engine temp stayed in the the middle of the gauge most of the time, but it did shoot up very high a couple times, but then returned to the middle before she was able to get it home. The low coolant light was on-my XK8 has a small leak...somewhere. I've been adding a very small amount of coolant once every 45 days or so(its been doing that since I bought it over 2 years ago, I can still live with that for a while). If I cycle between full hot and full cold, the heater will work for a few minutes, and then go cold again. I replaced the thermostat 2 years ago.
Since the bottom hose is cold, could the radiator be clogged, or is that a sign of a faulty thermostat?

 

First off I would remove that hose that bulging like a baseball is inside and see if the hose has collapsed inside creating a blockage. See what is going on with it first.

 

I would be very concerned about overheating the car, and would not drive it at all until this is resolved. Unless you have the Jag Wrangler's real gauge, the temp gauge just sits in the middle even when the engine is running hot, then AFTER it over heats, the needle goes up. Real Gauge is well worth the small investment.

I have seen intermittent over heating (on other cars, not my XK8) where the radiator hose collapses because it is weak and can't hold its shape. The suction produced internally with the fast flowing coolant collapses the hose, effectively blocking coolant flow. Then, when the engine speed slows and coolant isn't flowing as fast, the hose opens up again, and the temp comes back down. This can go on and on cycling like that. If you have an obvious weak hose, I would consider this a real possibility and replace at least the upper and lower radiator hoses. And for insurance, I would replace the thermostat while in there, it is cheap money. They can be sticky.

 

Dave,
Stop driving the Jag until it's fixed. If you have a small leak in the system it is probably sucking air as it cools and you may have an air lock. As the others have said. replace the upper and lower hoses, swap the thermostat and find the leak. If that hose bursts you may find yourself with electrical issues as well. It's time to get your hands dirty.

 

SteveJacks, That's some useful information about the temperature gauge, I always wondered why it never moved. I looked up and found the Realgauge for $110. Is that something fairly easy to install? I'm stretching my mechanical abilities swapping out the thermostat by myself(I found a tutorial on here I plan to follow). I ordered the hoses and new Thermostat today.

 

You can view information on the Realguage on Steve's page RealGauge FAQ - TheJagWrangler He also has a lot of other information. However, you need to find the cause before you cause damage to your engine.

 

Great information provided by everyone who has contributed thus far. You don't want to take ANY coolant leak lightly with these cars. Lots of potential weak points in these XK8 cooling systems due to all the plastic parts and if you don't take the time to find and fix your issues, you are whistling by the graveyard and eventually a weak point will crack or burst and you're likely to burn up your engine. Park the car until you can troubleshoot it and fix it. You'll get plenty of help and guidance here if you just ask....

 

I am not sure that this is a problem with your car but it has been identified that mixing two different types of antifreeze could cause gelling that could cause a clog in the system. It would be best that you consider flushing the system and install one type of antifreeze as you begin your troubleshooting to find the cause.

 

Hi Dave,
The forum will help you with the hoses and tstat. Search the forum first, as others have written about their experiences wit this procedure, and if you get stuck, ask for help. Many members are here and willing.

Regarding the Real Gauge, just to be clear, the "Steve" mentioned in Gus's earlier post isn't me, it is another forum member. I just simply am a big fan of the product, and have it installed myself. I would say that if you can replace your hoses and tstat, you can probably install the real gauge. The instructions are excellent, and support from Whitexkr (Steve) is excellent.

 

If you can change oil in a car, even change a air filter then doing the tstat stuff is easy. Lucky for you, you have a model year that you can switch the tstat housing over to alum made one, that I would do if/when you replace the tstat and housing.
I second getting new hoses on that car. As you will see, the Jag hoses are pricey, don't get them, look on ebay and get the off brand ones. I put the URO brand ones you see on ebay on mine.
If you have a DROID Smartphone you can get the Torque app with the ELM adapter to look at your temps thru the OBDII port.

 

Several gauges are out there, but this ScanGaugeE is inexpensive and sells for $94 at Amazon. And, it is PLUG & PLAY, you simply plug it into your OBD socket, run the line somewhere clean, stick it where you want and you can monitor most everything you could want. I ordered one today and can't wait to plug it in!

 

ScanGauge is a good product and you can continuously monitor all available OBDII data plus has trip computer features. It is plug and play.

Unfortunately oil pressure is not available over OBDII. This is one of the areas RealGauge has an advantage if you have the dummy factory oil pressure gauge. RealGauge also let you maintain a completely stock look and and has preset audible alarms for coolant temperature and oil pressure. Obviously it does require installation.

It all depends on what is important to you.

 

I already had a friend replace the plastic housing and cover for an aluminum ones 2 years ago. That looks fine, so I'm leaving the housing connected so I don't have to mess with those 2 difficult to reach 8mm bolts in the back. I've removed the thermostat cover, and it looks like there was a paper/fibrous type gasket between the thermostat cover and the thermostat housing, in addition to the rubber O-ring thermostat gasket. Is that correct? Because my local parts guy and the online parts fiches don't list a gasket for that connection.

 

If it's just a o ring you need a gasket, but usually it's a slotted o ring that the thermostat sits inside of.

 

Yes, it is a slotted O ring surrounding the thermostat, but any idea where I can find the fibrous gasket that goes between the housing and the cover?

 

Mine does not have a fiber gasket, maybe yours is different.

 

The split 'O' ring is all you need. There is no reason to add the paper gasket.

 

Thanks guys, I guess that's why I couldn't find a stock one online, I'll just add a tiny bit of silicone. I figured out that when I replaced my housing 2 years ago, the 'kit' came with a fibrous gasket. I also found in another thread that I'm supposed to discard the O ring that came with the thermostat, and use the thinner 'kit' O ring. Not ideal, but the old O ring still looks pretty serviceable, a little thinner. Any thoughts on that?

 

another area that develops small leaks is the hose between the stat and the housing by the windshield it becomes very brittle over time and cracks i replaced mine with a regular rubber hose .

 

Just a word of caution - Not sure about your year but my 2000 XK8 had (past tense) 1/4 turn to full tight on the thermostat housing bolts. Past tense means I overtightened and stripped one on reassembly. Replaced with a new bolt/washer and nut assembly.