I have a 1993XJS that just started to over heat. I remover the cap from the header tank and floating on top of the coolant was this thick brown molasses looking stuff. I think it got into the radiator. Does anyone know what this stuff might be? I have never used Barrs stop leak in the car but I got the car used a few years back. Thanks for any help.

 

That stuff is usually oil, either engine oil, or auto trans oil.

The following is primarily based on a 6 cylinder car. If yours is a V12, it is possibly a 6ltr, and some of the following applies.

The trans oil goes through a cooler matrix inside the radiator tank, and they can spring a leak and leach trans oil into the coolant, and sludge forms and overheating follows very quickly. This is in the LH tank of the radiator for a 6 cyl, no idea for a 6ltr, but RH side for 5.3ltr.

The engine oil into the coolant is usually via the oil passage/s in the head gasket, The V12 does not have oil passages the same as the 6, hence my assumption ???.

Stil with me, GOOD.

If it is a 6cyl car you "possibly" have a power steer cooler in the opposite radiator tank to the trans cooler, RH tank, and they spring leaks also. The V12 6ltr, I do not know, but the 5.3ltr has the power steer cooler outside the radiator so NO effect on sludge.

 

It is a 6 cyl. I have a service manual but it does'nt say much on the radiator. Is there any way or telling if it's the head gasket or the trans causeing the problem? Would a compression test tell me any thing?
Thanks for the help.

 

OK, now we know what we are attempting to fix.

I dont think a compression test will establish anything for this issue, as I dont think you are getting compression gases /pressure into the cooling system.

The oil passage through the head gasket "usually" weeps to the outside of the engine, but, it could just as easily track to a water passage, and oil pressure being way higher that coolant pressure, the oil will go that way, but when the engine is shut down, oil pressure is zero, but coolant pressure is 20psi, and coolant will go to the oil passage and then the sump. SO, is the oil in the sump milky, or still OK. If it is still looking like oil, then I doubt the head gasket is at fault.

The trans cooler is in the RH tank of the radiator, and they do fracture, as I said, and again since trans oil pressure whilst running is way higher than coolant pressure, the same thing occurs, oil in coolant, but coolant back into the trans is also a real problem, after shut down, SO, is the trans oil off colour??.

If neither oil is "off" then the sludge may be as simple as some person??? has mixed coolants, this is a NO NO, as they can/will turn to sliudge, and block all sorts of coolant passages, and overheating is quite rapid. The fix here is a long drawn out flushing of the engine/heater core/radiator core/etc etc.

Let us know, it is fixable, after all it is a Jaguar.

 

I took it to a mechanic and he does'nt think its a head gasket. I drained and flushed the radiator an engine. Now I'll drive it and see what happends. The coolant did look kind of red.

 

Don't wait to see, be proactive and check again for sludge after a short distance, say a few miles. Failure of the transmission cooler inside the radiator is a fairly common fault, certainly I have heard about it in the UK Jaguar Enthusiasts Club. You say it just started to overheat, indicating sudden failure of something, and my bet is the tranny cooler. Engine oil in the coolant due to head gasket failure normally creates a mayonnaise-like sludge, due to the additives in the engine oil.

 

I will be keeping an eye on it.