Okay, well after almost a year and 7,000 miles of mainly trouble-free driving, the apparently-inevitable finally happened. I was on the interstate this morning happily motoring along when I looked down and the temperature gauge was WAY above normal. I was in the left lane, but got over & off to the side within about half a mile. Got it towed home. Based on what I saw, I believe that it is a blown coolant hose, but all of the steam was from the back of the engine compartment, not the front (maybe the heater supply hose??). This is a 1991 XJS Coupe with 79,000 miles and the original V12.

I presume/hope that there is a collectively-agreed stepwise process of what I should check for before I attempt a re-start. Of course, I'll track down the hose, check & refill coolant, check the oil, etc.

Hopefully Grant has some words of wisdom (or even better, one of those nice, detailed pdfs....)

Thanks,

Brad

 

Heater hose, yes, likely

You'e already pegged it: find the offending hose, replace, refill, bleed properly

Access isn't exactly a pleasure cruise but it's doable. I'd replace both heater hoses while I had my hands dirty....as well as any others that are the least bit suspect and/or of unknown age.

Slice the old hoses off the nipples rather than twist-n-yank. Of course you'll want to make sure your new hoses look correct first.

Properly bleeding the system is important, messy, and a bit of a pain so while the system is opened, now's the time to do any other replacements you've been pondering. The fewer times you have to bleed the system, the happier you'll be.

It might be just a loose clamp. Fingers crossed. Speaking of clamps, using new ones may not be a bad idea as sometimes the old ones don't tighten evenly. At least clean and lube the old ones so the screwing-in action is smooth and easy. When working in tight quarters any little aggravation is magnified !

Cheers
DD

 

I've overheated (not pegged to the red H) but probably 75% of the way up twice. Once I was flushing with a garden hose car running I go inside to get a drink and forgot the car was idling with probably very little coolant it was certainly boiling the tap water, another time I forgot a vac hose was off and probably leaned out the fuel waaay too much. This was years ago still driving it daily no apparent harm.

It can get hot but as long as its not pegged to the top of the gauge I'm mostly certain your fine. Which is not to dismiss the overheat concerns on V12s they often come with clogged rads and can drop the valve seat thingy if it really overheats but the paranoia is unwarranted on a maintained system.

 

Brad, MAAAAAATE, its BEER O'CLOCK.

Words of wisdom, HAHAHAHA< Graham would smack me seriously if that took place.

Replace ALL the coolant hoses, and clamps, as Doug said, dont mess around.

Remove the steel header tank in the LH side of the engine bay, flush all the mud out of it.
Remove the atmospheric tank, the hidden on, and flush the mud out of it also.
Replace BOTH thermostats, and I mean the CORRECT stats, with OE gasket.
Replace the pressure cap, the one on that metal tank, and make sure it blows off at the set pressure, not simple, but I have had a few duds over the years, and chased all sorts of shiiit for a $5 cap blowing off at 4lb instead of 13lb.

Read that new sticky at the top of this section, "Worksheet............", and BEER mate, lots of it.

I reckon you have NOT damaged the engine, only when you start it after all that work, will you know.

 

Good to hear, Grant- especially from you.

Okay, so the problem has been identified. The heater hose from the right bank to the heater control valve. Bad tear on the inside of the elbow.

I had already replaced some of the hoses, cleaned out the header and the atmospheric tank - but I didn't replace the thermostats. Okay, off to the parts search.....

Thanks!!!

Brad

 

Listen to the valves on start up. If you hear the tick - tick - tick of valve tappets it means the seat has moved. That’s not good. The only way it can move is down, indicating loosening of the seat.

With respect it’s extremely rare to loosen a valve seat with one overheating. That normally only comes from many repeated overheatings.

 

Okay - so, I replaced the block-to-heater valve hose, which had blown at the inlet elbow.
.
Replaced the hose from the heater control valve to the heater core, too.

Also, replaced the reservoir tank (the old one had a pinhole leak in it).

Refilled the system - it took about four gallons to get it back up to full.

When I went to start the car (front end elevated, LF elevated a bit extra, "B bank" vent plug out, system open & full, per the procedure that DD describes), water SHOT out of both the filler tube AND the B bank vent. I was hoping it was just a 'burp' from a bubble back at the heater core.

I installed the vent plug, capped the system and started it up. Ran rough, but it ran. Not wanting to run too long, I shut it off, planning to check level, top it off, and prepare to let it warm up for the full system refill/bair bleed process.

There was a sound I've never heard in an engine before. It reminded me of my own guts/innards when something I ate doesn't agree with me and there's a lot of gurgling going on. I could hear lots of bubbles moving around. I attempted to open the system, and there was a LOT of pressure built up.

I haven't seen an increase in oil level, but I'm starting to wonder if I've cracked a head. It just doesn't sound or feel right to me, and I'm hesitant to do anything else for fear of just compounding the problem.

Cracked head? Cracked block? What have I done?!??

Brad

 

I would top it up until water comes out of the wing tank cap spout, close that cap. Top up the centre spout, remove the bleed screw from rad top LHS, place the RHS aircon control on DEFROST, start the car, and keep topping up the bleed hole if the coolant level goes down while it runs. I think you have just got the system with loads of air everywhere and it needs to come out somehow.
Keep the car running and let the system settle. I very much doubt there is any damage.

 

I agree.

I reckon she got a belly full of air.

I usually remove the small vac hose on the heater tap, and ENSURE the tap arm is in the DOWN position, as this is FULL ON.

Partially full systems, mainly teh V12, are a fair mongrel to bleed. Some I have drained via the bottom radiator hose, then started from scratch.

As I am a rather odd guy, my big container of coolant is on the bench, and the car is some 25 steps away. I use a 1ltr bottle, and pour that in, walk back to the bench, refill the 1ltr, back to car, and so on until its full and bubbling out the radiator bleeder and tank spout (as Greg said). Sometimes when I return with the next 1ltr, I can still hear "gurgling", so I wait before adding more. It takes time, who cares, the beer fridge is alongside the car.

Once the bleed at the radiator is clean of air bubbles, fit the plug, then top some more via the filler spout, until the header dribbles out, cap it, top off the filler, job done.

BUT

Some cars will bubble out the header tank., before the radiator bleed, thats life, the XJS be female, do the maths guys, you are that clever, surely.

Since you have drained the header tank for repairs, I have not mentioned that on the HE this MUST be drained separately from the system, or filling and bleeding will drive you nuts. The PreHE drains that tank with the rest of the system.

I doubt there is issues also. The usual is a very loud clatter from valve seats. Cracked head and block, never seen one, as with head gaskets, never seen one. If you really COOKED that engine, different discussion, but you have not, that I can understand.