Blown Head Gasket
 

1987 Jaguar xjs V12- numbers matching. Pristine condition, and a 3 year old paint job (champaign). Bought it for 2k on a hunch that the owner was wrong about a it having a blown head gasket. There is no smoke or excess noise. The oil is not milky colored. Idles and cranks smoothly. It does have a lack of power however. It does overheat. The car leaks about a quart of coolant on the floor over 1-2 weeks. I have already replaced a cracked coolant hose which helped dramatically. Could the fact that the cooling system cannot fully pressurize because of the leak be the sole cause of the overheating? Additionally are there other ways to check for a blown head gasket without tearing into the engine? I can't take it to the mechanic for a couple weeks because I'm short on money.

All the best,
Lou

Common things that can cause overheating:

Air in the cooling system
Debris between the evaporator and radiator
One or both thermostats not opening
Bad clutch on mechanical fan
Foam shroud around radiator missing
Plugged radiator core
Leaking radiator Caps

IMHO the best way to check for a blown head gasket is to test for hydro-carbons in the coolant. You can buy a "block test kit" (about $50 from NAPA Auto Parts) which uses a liquid dye or take it to a shop that has an exhaust gas analyzer....which can be used to "sniff" the coolant.

Go through Don's list and there's a 99% chance that you'll fix the overheating.

Cheers
DD

Thanks to all for the quick response. and i just took it for a drive, and to my surprise, not once did the electric fan come on. Troubleshooting the fan today..

Hi, how did you get on the end, did you fix it?

Thanks.

I spent several days checking different parts of the cooling system. The car sill overheats with the electric fan remedied. Then I made sure there were no air bubbles in the cooling system. After that, I replaced the radiator caps. (one was slightly leaking but both were replaced for good measure) The PO said he replaced the thermostats and I am sure he did because he gave me the old ones with the car. There is a mystery smell of evaporated coolant in the garage after running it. Now I am looking for leaking hoses. I already found and replaced one cracked coolant line which helped dramatically but the smell remains. I might just have to bring it to the mechanic but money is tight right now so it will have to wait a little bit longer. continuing with self diagnosis attempts...

Ok, thanks for the update ECBJAG.

Good luck with the further checks. Have to keep us posted. Be interesting to see what's at the bottom of this.

There is UV radiator leak detector dye you can get from Autozone. It's a small bottle. It empty the whole bottle to your radiator and run the car normally and the look for the leak in the dark. You'll need a UV lamp. I used it to locate a coolant leak in my BMW.

that is very helpful info bigwiki! now all i have to do is find a UV lamp!

Update: Today I took the car for a drive after repairing a suspected leaking coolant hose. The car never overheated although after a 10 mile round trip it was creeping up toward the "N". It seems like a mild problem as of now. When cruising at high speeds the car runs well and cool; it's stop lights that kill it... THEN: upon returning home I found the possible source of my electric fan problems: a blown inline fuse for the electric fan which has been inop since I bought the car (it has been overheating since I got it in July so I haven't even really got to drive it yet!) I will take it for another drive in a couple days, observing how much coolant is still leaking onto the ground and seeing if the electric fan works! wish me luck! if I could fix the overheating all that would be left to fix would be the strange delay from the gas pedal to the engine response.

"Moving towards" the "N" is fine, usually.

You might want to buy or borrow an infrared thermometer (you know...they look like a ray gun) and check temps at the left and right water rails and then look at your gauge. It's nice to know what temperature corresponds the the "N" rading on your guage....and it can vary quite a bit from car to car....as much as 20º. The gauges are not all that great.

As I recall the bottom of the "N" on mine was about 180º and the top of the "N" was about 195º. Yours may vary.

Anyhow....

It's good to know if your left and right banks are about the same temp as it suggest proper coolant flow thru the system and the segregated radiator. This is important because "overheating" is the typical sense isn't necessarily what hurts these engines. Lack of proper flow can cause steam pockets....localized overheating....in the cylinder heads even though the overall coolant temperature is well within the safe range.



Cheers
DD

Ok. I'll see if I can find my Infrared thermometer :-). Reading other threads about overheating it sounds like 220 degrees is technically overheating? I am starting to suspect a marginal radiator because at cruising speeds there are no problems but at stoplights when it loses air flow, it starts creeping up. The thermostats are new so I believe they are fine (unless I got duds) Another thing is that it is pretty cold here right now, 40 degrees average and it could be masking a more serious problem.

Pull your rad...I'll bet it's at least 30% clogged with leaves and debris.

Your e-fan will make a difference, too, as will a good fan clutch

Cheers
DD

will do as soon as I can. how difficult is it? is it a diy worthy job?

As radiator removals go, it's a PITA....but entirely DIY-able. The lower radiator hose is what makes b*tch to deal with. The rest is straightforward enough.

I strongly suggest having a helper ready when the time comes to lift it out or you'll bang it up pretty badly. It has to be lifted up and canted rearwards simultaneously. Awkard for one person to do on his own

Cheers
DD

After 8 months of struggle I finally broke down and saught a power greater than myself as the spring months creep in and the problem intensified- the local mechanic. He has the car now and will get to the bottom of it. I found the radiator job best left to him if need be. :) I should have closure to this in a week or so an a working car! :) will keep up to date..

The mechanic found the radiator to be over 50% clogged. The electric fan was shorted/fried. The hoses on the Y pipe by the water pump were leaking badly. No blown head gasket after all! 2k in repairs to the cooling system but if it needs to be done what are you gonna do?

any word on the power problems?
If its just a delay that could be the tranny, hows the fluid in it?

Yeah actually. The fluid in the tranny is fine but the mechanic said it was just the TPS. Its a 330 dollar part so I was just going to buy it and install it myself.

ahh yeah thatd make sense. Def a good idea should be a pretty easy job


tbh with you man Id go check that **** out in a junk yard because thats pretty pricey for that little sensor.