Went out to the garage this morning, and there was puddle of something behind the XJS.

Determined that it must be coolant; however, I replaced all the belts and hoses about 9 months ago and the car has never run hot. After visual inspection, I can't see any obvious sources of any leak, and it looks like coolant was first hitting pavement around the front wheel.

So, I surmised it must have expelled after shutdown.

How do I tell if it's the caps, the thermostats, the expansion/overflow thing, etc.?

Should I refill and start the car?

Thanks in advance.

 

When you've got a little time to kill, pull it out of the garage, start it up and let it run. I would think that once it's up to temperature the leak will reveal itself.

My guess would be that a hose clamp has worked its way loose. They require periodic tightening after being replaced. It's surprising how lose they can get.

Let us know what happens...

John
1987 XJ-S V12

 

That's a good suggestion, but if it were a faulty thermostat isn't that a bit unwise?

 

I reckon the suggestion you got is as sound as it gets.

Which wheel is the puddle near, as I cant quite see it from here. LH or RH?. That wil determine what is in that area to look into.

A bad thermostat will not leak. OK, its consequences could eventually cause a leak.

My bet is on the hoses you have been in touch with.

The caps maybe, but witness stains on the centre cap are easily visible, and the atmospheric tank is huge, and plastic, and rarely leaks until overfilled.

There is a "Lo Coolant" sensor in the metal header tank, in the LH front of the engine bay, and it is held in place by a simple rubber grommet, and they leak quite often.

 

Apologies, I should have mentioned which wheel. It was the LH front wheel.

Last night I pulled the wheel and examined the hose going to the plastic overflow to make sure it wasn't blocked (even though it was replaced with all the rest). There was a little gunk, but not enough to prevent flow. The overflow was full and there were signs of fresh coolant around the base of the container.

Does that help point the way?

 

OK, I'm baffled.

I refilled and bled the system per Doug's procedure. Then I let it get up to full temp including up to the point that the electric fan comes on, and there are no leaks. Temp never got above the bottom of the N, and I used an infrared thermometer to check temps around the engine.

It took a gallon and half of coolant to refill the system, and as I mentioned the overflow plastic tank was full. Something is out of whack, and I have no idea what it is or where to look.

 

OK, my findings after a few years with these beasts.

They purge "about" 600ml from stone cold to normal operating temp.

Anymore than that, significantly, means an issue.

Most common is a dud pressure relief cap, the one on the metal header tank in the LHF of the engine bay. Getting caps that actually blow off at the specified pressure has led me to drink, they are rubbish in the general market, and brand seems to have no special deals. Dowm here we have CPC brand (well respected of old), and I recently went thru 7 in our stock at work to find one that blew off at 13psi as stamped. The balance were all over the place, from 4psi, to 23psi, not good.

The plastic atmospheric tanks a prone to MUD build up in the bottom, sometimes 3" thick. This then causes the hose/pipe that drops into this tank to actually sit IN the mud, and the cooling system cannot breath, and that causes all sorts of drama. Remove that tank, clean it out. Half fill it upon return.

Check the metal joiner where the hose FROM the header tank travels thru the grommet at the rear of the engine bay, near the LH bonnet lock, that steel joiner plugs up regularly.

The heater tap, dead centre at the rear of the V12, is a very common leaker, and almost impossible to see. The coolant can drop anywhere under the car, and often not related to that position. For $20 for a generic vac heater tap, replace it regularly.

These engines, and others, will "suck air" as they cool down, as versus coolant from the overflow tank, its easier, and that is a pain to find. The suspect does NOT leak coolant OUT, but allows air IN on the cool down. Most common on the V12 are:
The 2 caps,
Heater tap,
LO Coolant grommet in the header tank,
Hoses (you got heaps),
Water pump seal (RARE),
Top hat seals on the water rails on top of each cylinder head.
The radiator is starting to clog up internally (clutching at straws at the moment with this one), but they require cleaning regularly.
I'll keep thinking.

The fact its running at sweet temps, the stats are NOT on my radar at all, nor is teh fan hydraulic hub.

Check the small pipes that run across the top of the radiator support panel, they should be HOT. If they are, OK, if not, then they, or the banjo fiasco on the RH top of the radiator is blocked.

My atmospheric tank is the "Moreys bottle" and it is 1ltr capacity, and been there for years. Just too slack to remove the label.



I will keep thinking, and come back when sparks fly in the brain.

 

OK Grant, from looking at your list I surmised that the first and easiest step was to replace the two pressure caps since they are inexpensive and easy to find.

I also pulled off the wheel again and pulled out the atmospheric/overflow tank and cleaned it out to make sure there wasn't in "mud" in the bottom, and disconnected the overflow hose at the cap fitting and blew air through it to clear any gunk or obstruction out.

I put a couple of inches of fresh coolant in the atmospheric/overflow tank and refitted. I'll check the air pipes to see about the banjo bolt.

 

Checked the small pipes that run across the top of the radiator support panel and they measured 164 F / 73 C on the infrared.

I'm now nearly certain that the coolant leak was from overflow of the atmospheric tank, so hopefully the new caps will solve it.

Any other suggestions before I start to drive it again?

 

Have a drink.

Smile properly.

Enjoy the beast.

 

Since replacing the caps, I've driven the car a dozen times and I make sure the trip will be long enough to get fully up to temperature. I've avoided trips taking me too far away from home until I'm sure the system is working properly.

So far, no drama, no spills, nor does the needle move above the bottom of the N.