Hello!

Here's the scoop. 1987 Jaguar XJS 75,000 miles.

Been sitting for about a year.

Drove it for about 150 miles, no problem! Then, it looked like it started overheating. I let it cool a bit, but it still squirted some coolant when I popped the radiator cap. So, I took a hose and lightly rinsed off the engine.

I drove about 10 miles and the oil pressure gauge reads super-low, the red warning light comes on, and the temperature gauge goes way up!

So, next week, I changed the oil with 20w50, capped off the coolant, and started her up. Seemed ok! Temp good and oil pressure went to 50 psi. Then, after about 10 mines of driving, same things started happening! Oil pressure dropped, red warning light comes on, and temp goes way up! I read a ton about faulty gauges, so I kept driving.

After a while longer, she started blowing some white smoke (possibly blown head gaskets?), but that went away.

Any idea what could be wrong? If water got in the distributor, it would've dried after a week...right?

Thanks!!

 

Another thing to add - someone earlier had changed the thermostat, but when I turn the header on inside, there is no heat.

Could the thermostat be bad?

Also, when the car was overheating, there was a ton of pressure building in the radiator. Does this mean it's flowing through the engine?

Could it be a bad water pump possibly?

 

You have two thermostats and, yes, one or both could be bad. You can test them in a pan of water on your stove and a thermometer. Or just replace them. Make sure to get correct replacements that have the bypass disc on the back.

The cooling system will work on these cars but there is no reserve capacity. Everything has to be 100% up-to-snuff: thermostats, radiator, fan clutch, aux fan, hoses. If anything is sub-par, you're in trouble :-)

As far as the radiator goes note that they are often clogged *externally*. Remove it and you'll like find a huge pile of leaves and debris blocking much of the air flow. Of course, they can clog internally as well....like any other radiator

Low oil pressure when warm *at idle* is common on the V12s....even on the few that have accurate gauges :-). At anything above idle the pressure should come right up, though.

You can check for a blown head gasket by using one of those dye kits that detects hydro-carbons in the coolant (NAPA sells them, among others). Or, a shop with an exhaust gas analyzer can "sniff" the coolant to detect hydro-carbons.

I'd want to find out if the head gaskets are blown (or not) before spending much time or money on the engine. Replacing them is a big job on a V12.

Cheers
DD

 

Oh, the heater not working could be from a variety of causes, including air in the cooling system....which will also cause overheating. The V12 cooling systems need to be bled to work properly.

Cheers
DD

 

Thanks Doug!

The fans under the hood do come on, and they stay on after I turn the car off for a few minutes.

Hmm, I'm not sure if they replaced both thermostats. Do I run any risk of hurting the car if I just pop both thermostats off and drive it? Of course, it won't warm up completely.

I've heard people talk about a stuck advance mechanism. She doesn't seem to have full power, and I know the kick-down switch won't work. I don't get that "throw-you-in-the-back-of-the-seat" feeling.

Ah the joys of an old Jag, but I want to get her running very well!!

Thanks!!

 

I don't see where running without thermostats on a temp basis would cause any harm BUT the fuel injection system likes to see 175-180ºF before it stops enrichening the fuel mixture....and running rich over a period of time isn't good at all. It'll wash down the cylinder walls. Better all round to use the thermostats.

Pop off the distributor cap and give the rotor a twist....it should spring back sharply. It probably won't. Also check the vacuum advance as the diaphragm often fails.

Cheers
DD

 

Sounds like Charlie Allthumbs has struck !

As said here, there are two thermostats, (one per bank), and also there are bleed valves in the coolant circuit to make sure all air is removed when changing the coolant. Air pockets will prevent coolant circulation and cause overheating. White smoke from the exhaust could be oil or brake fluid, or, of course, steam from coolant boiling off because of head gasket failure.

Rmember, this car is 23 years old and if all the regular maintenance has not been done, is likely to prove troublesome until you have caught up on others neglect.