If you think the coolant is still somehow getting past the cap then one or more of 3 things could be happening if thats true. 1: The cap is defective (probably not since it's new) 2: the tank is not sealing against the cap and leaking into the overflow 3: The pressure inside the expansion tank is greater than the caps rating and is coming out. Excess pressure could be caused by the car being overfilled or the car getting too hot, even a blown head gasket. You can check this by installing a pressure tester onto the expansion tank and allowing the car to warm up.

I think to make sure the coolant is being lost into the overflow, you can pull the tube upwards out of the tank and stick it in your own clear bottle, secured and out of the way of moving parts. Then you can let the car warm up and observe if its actually pushing water out to the overflow. Just some more ideas!

 

It's definitely pushing coolant out into the overflow - definitely. It's a one way trip. I have measured the level in the catchment recovery tank, and it will perpetually rise until overflow.

I have done the pressure test on the header expansion tank, and there are no leaks. There are also no exhaust fumes in the coolant (it was tested) so it's likely not the head gasket (and there are no error codes - I assume a blown gasket should throw one). The threads on the header expansion tank look good and I have meticulously cleaned it so it's hard to believe it's that. It's possible that this tank may also have a pinhole leak that may be evident at high pressures/hot temp so a cold pressure test may miss it, right?

I was told that I may have a pinhole leak in the plastic line from the header expansion tank to the overflow recovery tank - enough so that it won't lose a significant amount of coolant from there but it will cause a loss of vacuum so that coolant goes on a one-way trip to the recovery tank when it gets hot enough to leave the expansion tank. I am next going to replace this and place a new cap on the expansion tank. If this does not fix it, it's just a nightmare--and I do not want to just throw parts at this.

For the pros:
1. If there is a leak in the heater core, would this cause a loss of pressure in the system to that coolant will leave the expansion tank into the recovery tank? (I appreciate that it would cause a coolant loss but I see no evidence to suggest this and, again, the major symptom is overflow into the recovery tank).
2. If the thermostat is bad, would this cause perpetual pushing out of coolant from the expansion tank (presumably because it gets too hot)?

I really appreciate any continued thoughts, guys. I will always report back to help others. I know there are others who had experienced identical problems to this, but there was sadly no follow up after advice was given, so now I'm being a pest.

 

1. No means air in the system, this can expand and contract.
2. depends which way the tstat has bust.

Have you changed the header tank cap for a new one?
Have you changed the tstat recently?
Have you confirmed (eyeballed) each individual hose from it's point of origin to it's end place from the coolant hose schematic?
Any issues with the heating?

 

If the heater core really was leaking, it could prevent the cooling system from creating vacuum when low and drawing coolant back in on cool down.

 

I'm doing your suggested experiment right now. I installed a secure, clear additional recovery bottle. After 25 miles, it jumped around 250mL of coolant into the bottle. I marked it and we'll see if it stays the same or gets smaller (I hope). This volume would probably be enough to reach the overflow elbow in the recovery tank near the left front wheel. That's my feeling. We'll see.

Edit: Of that 250mL that flowed over into my make-shift recovery tank, around 125mL of it appears to have been drawn back into the system this morning - overnight cool-down. So, it appears that the vacuum in the system may at least be partially operational.

Incidentally, I'm sure there is still coolant in the real recovery tank - small drips still seen coming from that tell-tale splash guard at the left front wheel even with the coolant now being re-diverted into my new auxiliary recovery tank. I *hope* this is (at best) residual overflow in that tank from before or at worst a symptom of maybe a minute fracture in that tank.

Other than the overflow, recovery tank, is there line in that region that would cause coolant to fall there? I swear I see nothing from the hoses up top or from the radiator which looks great.

 

The only thing in the fenderwell in that area is the overflow tank for the coolant. I am hoping its just splashing out or that it has a crack up high (if its cracked on the top, it will still work good.)

 

That was my feeling, too.

Thanks again for suggesting the auxiliary overflow tank - I had to work at the other side of town today, and after a 55 miles, fast drive, my 500mL auxiliary bottle was near filled. That is DEFINITELY way beyond the limit of the overflow arm on the recovery tank beside the right front wheel, and now I have my answer (a lot of that would have ended up on the road) - for sure it's likely coolant getting past the cap. I'll check on it tomorrow morning and see how much (if any) gets sucked back in.

I will be near the dealer tomorrow, so will replace the cap, and the line from the expansion to recovery tank and then repeat this experiment, and report back. If there is still a lot of coolant getting past, I'll have to look for other ways it's losing the vacuum in the system.

Any additional suggestions and I'll try it. Many thanks!

 

Thanks for the update SC and we're keepin our fingers crossed.
A little bump here to keep the thread at the top of the pile and interest alive.......

I'll be checking back in to see how it goes......This is one thread I'd like to add a "FIXED" to the title of. Thanks for your perseverance..

 

Update:

Replaced the expansion tank cap and expansion tank to recovery tank line with Jaguar parts, and I see the same issue - coolant being pushed back out in the recovery tank (also into my makeshift recovery tank). It seems that it's not losing vacuum from the expansion tank onwards. It was pressure tested again, and no leaks.

I can now verify that the water pump has been replaced (before I took ownership), and it's not a plastic impeller. However, there is a partially melted thermostat housing and a black residue around a dodgy-looking thermostat that makes it look like someone may have experienced a similar issue (coolant loss) and poured radiator seal in there like a not very smart person.

The thermostat and housing are now replaced, and the issue persists - coolant being pushed out. One side of the radiator is ice cold, and there is WAY too much pressure in the cooling system - if I release the expansion tank cap, it pushes a jet of coolant out into the recovery tank.

So, I'm left with wondering why on earth there is so much pressure. It screams of heat gasket, but there is absolutely no exhaust fumes in the coolant, and coolant does not appear to be getting into the gasket.

Is it possible that either radiator seal (or mixing of coolant) has blocked one side of the radiator? This might explain the high pressure in the system, coolant push out into overflow, cold radiator in one side, and also intermittent hot and cold heater issue.

Would you guys replace the radiator next?

If anyone has seen anything like this, please help me out and comment.

As always, I will keep you posted.

 

Yep, change the rad. End of.

 

That was next on my agenda, but can you please tell me why you think it's the radiator, and please excuse my skepticism in the interim......

Do you have personal experience of this?

 

sure, it sounds like the car has had everything but the rad changed.

I've had similar on 6 pot Jaguar engines, and now you've supplied information pointing to a stop leak product being used to cure an as yet unknown cooling fault, your core could be furred up and partially blocked with the stop leak.
Lets recap as the thread has a lot of wordy posts.
New thermostat
new T stat tower
New header tank and cap
new expansion tank
new water pump and gasket
New coolant

So, the rad takes all of 10 minutes to remove once you drop the coolant. I'd suggest running the car with a coolant flush additive and fresh clean water through after dropping the coolant. Run it up to temp, the last time I did it, the guide was to drive the car and put 50 miles on it, hopefully it will break down any stubborn blockages. I would have recommended this earlier had I known about the stop leak being used. These engines do not work well if that is introduced as you're finding out, as against say a Jaguar V12 which Jaguar recommend Winn's Leak Bar.

My comment about changing the rad is extreme, being in the UK I can have a good S/H rad at my door in 10 minutes, but it's obviously a more difficult task being in the USA and it being a Euro car.

After the rad flush product has done it's thing, drop the coolant, run fresh clean water through it, and add new coolant. See how it goes then.

 

Thanks for sharing your thoughts. The stop leak being used is by conjecture only (residue resembling this on the T-stat). I did not and never would use stop leak.

There is definitely trapped air in the coolant system somewhere.

I will report back in due course, and I appreciate any additional thoughts from others.

 

I have never had mine totally empty, so I dont know how easily these things can trap an air bubble. I know the 4.0 LS motor is terrible about this and requires a special bleed procedure, unless you use the radkitplus vacuum bleeding kit.

I wouldnt damn the radiator just yet. I see lots of cars where people put in crappy stop leak stuff and plug heater cores, but not so many radiators. I think it would be a good idea to drive the car like 10 miles and then feel each side of the radiator. One side should be slightly cooler than the other if the car was just stopped or if the fan is running. If one side is still ice cold, then the radiator is not flowing either because its plugged or air is not allowing the water to be pumped. Of course, if the radiator wasnt flowing anything, you would have trouble going far at all without it getting hot. Another free thing to check is to make sure that the cooling fins on the a/c condenser arent flattened too much. If they are, they can restrict air flow.

 

It sounds like you are in denial - One side of the radiator is ice cold, and there is WAY too much pressure in the cooling system - radiator.

 

This was helpful. Thanks!

 

Very bad news. Same issue (apparent 'airlock' in coolant) with new radiator, old radiator and heater core flushed, and heater core, old radiator, and hoses flush with no apparent blockages or debris coming out----pressure builds up in the coolant system, cold spots in radiator, rock hard radiator hose after driving not too far, and heater alternating hot and cold air.

Although there is no exhaust fumes in coolant at low idle (I assume they may appear with harder driving), this seems to me like a head gasket issue.

Has anyone ever seen a bad head gasket behave like this without exhaust fumes in coolant, blue smoke from exhaust, and all the other typical head gasket issues?

Would you guys suggest replacing head gaskets now?

 

one suggestion before pulling heads, run the car with the thermostat removed.

 

Please can you tell me why?

 

Another update:

For those of you not following this thread, I've had a perpetual pushing of coolant out into the recovery tank until overflow and then onto the ground which I can now identify as an airlock--seems to be pronounced when the heater is on (heater will transiently run cool, then will get hot again....when cool, two hoses in front of the radiator are HARD and cool when this occurs). When the heat runs cold, I can release pressure from coolant system by taking off radiator cap (and a jet of coolant will be pushed out into recovery tank....I assume this is what the system has been doing automatically as coolant loss was an intermittent problem.

Here is what has been done.
- No leaks in the system - negative pressure checks hot and cold twice.
- No leaks seen in any hose, the expansion tank, or the recovery tank.
- Replaced expansion tank cap.
- Replaced hose from expansion to recovery tank so there is not a loss of vacuum (preventing coolant from being pulled back as it should).
- Hoses on the front of expansion tank criss-cross as they should.
- Water pump is in good condition, and it's not the faulty kind with plastic empeller.
- No leaks in expansion tank or recovery tank.
- Exhaust fumes not detected in coolant twice--once with 3K rpm.
- No appearance of oil in coolant.
- Thermostat + housing was replaced today and issue persists, but radiator fan no longer comes on as much (presumably there was an overheating issue).
- No leaks in radiator.
- Radiator and heater core flushed, and everything was flushed under pressure forwards and backwards.
- Radiator was changed and issue persists (airlock in coolant system.)
- No smell of coolant in car, no wet carpet, and no symptom of a leaking heating core.
- Valves in heater look to be in right direction.

1. I'm open to the fact that this may be an atypical head gasket issue, but why no exhaust fumes in coolant?
2. I'm open to the fact that the airlock in the heater core or coolant system is unrelated to the coolant loss since replacing the T-stat and housing seems to have removed the radiator fan from coming on as much (and so I could surmise the coolant overflow into the recovery tank was because it was perpetually boiling before, and being 'pushed out').

I have a stumped master Jaguar tech here. Any insight would be most appreciated, and we can keep this a permanent post to help others. With brainiacs like you guys, I refuse to believe that nobody has seen this issue before.