Background: Replaced thermostat with OEM after confirming it opened at marked temp, pressure tested at 18PSI at a T in the coolant tank hose and pressure did not drop, found ECM was not grounding the IC pump relay coil and added permanent ground so IC pump runs with ignition on as it should, Purged cooling system at the tank bleed screw and the Supercharger fill plug, and topped coolant up to the max mark. Also confirmed that Auxiliary pump does not run.

I've since made test runs of 16 miles, 30 miles, and 50 miles with coolant temps staying between 195F and 204F and everything seeming normal, and then driving home from the grocery (12 miles away driven right after the last 50 mile test drive) my wife said it overheated again.

So... 110 miles driven since the above fixes and topping up the coolant with the temps running OK from 195F to 205F, and then it began to overheat again and my wife had to drive in short stints of a mile or so for 12 miles letting it cool between stints. At home after sitting overnight there was coolant around the radiator tank cap and blown back on the engine cover and it took 60 Ozs or 1-7/8 quarts to fill the tank to the max mark. When the ignition is turned on I can hear the electric Inter Cooler pump run and it continues to run about 10 seconds after the ignition is turned off.

My wife said when it was hot (246 F) the Ultragage would stay on for the same amount of time time it took the electric fans to shut off and would show 187F to 195F when it shut off. Hard to believe it would actually cool off that fast with the bonnet closed, so there might be something else going on with the temperature sensor.

Now I don’t know if it is overheating because it loses coolant or if it loses coolant because it overheats. Would 2 quarts low be enough to overheat? And the 110 miles driven before it overheated this time was about the same distance driven when it overheated the last time although then it was all the same drive with several stops.

I've let it idle for 20 minutes on ramps so I could check for leaks and saw none, and I checked the coolant level after the first 16 mile test drive and it was still at the max mark. I thought the IC pump was the fix but apparently not. Any ideas?

 

Under what conditions is it overheating? (stopped, in traffic, freeway?)

250F might overcome rad cap and blow out coolant

Did it overheat badly at the outset (bad thermostat?) Why did you replace t'sat?

If it did get really cooked, you might get the header tank sniffed for hydrocarbons (eg head gasket)

Have you pulled associated DTC's and looked at overheat history?

Any chance mismatched coolant types have gummed things up?

 

Sorry to hear you are still having problems Phil.

Apart from the previous suggestions all I can add is that on my car it is the auxiliary pump that drains the coolant tank on going thru the top up procedure.

The IC pump does not seem to play any significant role in draining the coolant tank at all for my car.

Do you get any hot air when you run the heating on full in the cabin?

Reason for asking is that I think the only way to fill the heater core is thru the operation of the aux pump.

 

The first time I purged the system I had the heat on max and there was hot air, but the ambient was 90 degrees F so it was hard to tell how much.

It overheats while driving at moderate speeds and it definitely blows coolant from the cap. The temp does not go above 246 on the Ultragage and that is enough to peg the dash temp gage and turn on the amber warning light. The UGs range is way above that, so I think the hottest it has gotten is 246 F; not sure why it stops there but it must be the temp it starts releasing pressure at the cap.

I replaced the T-stat thinking it might be the problem; the replacement opened slightly farther than the original one but not much, so I think the original was OK

There were no heat related DTCs or Jaguar specific codes related to heat the first time; I haven't checked them this time yet but I suspect it will be the same.

The coolant in it was the orange long life stuff and that is what I have used to top it up.

The fact that it can cool normally for 100 miles of driving and idling and then overheat leads me to think it is leaking, but I can't find it. I hope it is not the dreaded leaking hose under the supercharger, but shouldn't I see something on the ground if it is?

 

Have you replaced the coolant cap? It may not be holding pressure therefore allowing the coolant to boil and overheat. Getting a new one is cheap insurance at $8.

 

Also if the house under the supercharger is leaking you may not notice the coolant because it can evaporate from the heat in the valley unless it's a serious leak then there would be coolant runoff coming from the back of the engine.

 

I agree with BlackKat on the valley hose. At least that would be better than a head gasket.

When I did my valley hose at 106,000 the original looked fine and felt fine.

If your aux pump is not working then as others have said in this forum you should not be getting full heat on both sides in the cabin as the aux pump is the only way coolant is pumped thru the heater core.

Is it possible that a coolant low condition in the heater core could cause the symptoms you are experiencing?

If the system looks like it is topped up and then after so many miles coolant is forced into the heater core due to expansion then you would have a low coolant condition.

 

Phil

If you have a hidden coolant leak, you will smell coolant whenever the engine is warm.

- Do you?

- Ditto above; Check the cap with your pressure tester (sounds as if you have one)

- What was the run up to the original overheating episode?

- Any emissions test place can wand the header tank and confirm or eliminate head gasket failure (failing gasket would account for your 100mi to overheating)

- Is serp belt/tensioner in good shape? Check tensioner for torque and binding; ditto idler

- Another possibility is plugged radiator. Pull upper apron plastic and IR gun (or feel with glove) core after driving 10 miles. Should be fairly uniform temp. If bottom is way cooler, suggest new radiator.

- Just FYI, I had a similar issue years ago (Audi 200) which turned out to be a bin liner (trash bag) stuck between AC condenser and radiator; invisible till I had the radiator half out

Hope this helps...

 

Thanks for the replies, guys. Ii appreciate the suggestions

I thought that would be a good idea too, so I bought a new cap at O'Reilly's but it did not fit (it would start but not screw all the way down) and it was a 16 PSI cap not 140 Kpa (20 PSI) like the one on it. The old cap says FoMoCo and made in India, but it fits.

The original cap did hold 1.1 bar (16 PSI?) when I pressure tested with a T in the small hose at the tank with the cap in place. I think I had read a warning to not pressurize the radiator above 14 PSI so I tried to stop there with my bicycle pump and wait to see if there was any leak down; the pressure remained steady at 1.1 bar for over an hour.

Looks like my next job is to drain the coolant and pull the auxiliary pump to see if the pump or the wiring is the problem; the fuses do have 12Volts with the climate system on so the relay is working. The top hose on the aux pump has just a wire wrapped around it and no hose clamp so it is suspect as well.

I haven't smelled coolant except when it overheated and blew it out of the cap, but I'll sniff again. I don't have a cap pressure tester - just my bicycle pump with gage I used for the system.

The serp belt looks OK as far as I can tell. I'll call around about sniff testing the reservoir.

Original overheat was with my wife driving it at 133,096 miles. We had driven 7,000 miles since purchase and she had made a 200 mile trip the week before with no temperature problems. I trailered it home that time and started the diagnosis with T stat replacement, pressure test, and then on to the electric pumps. I've pulled the front bumper cover and grill and found no radiator blockage on any of the five radiators, and checked the main rad with a non contact thermometer and it seemed OK. I've driven only a few hundred miles since the initial overheat and twice drove 100 miles before it happened again.

 

Phil, you can (carefully) reach the auxiliary pump and feel it running. You don't need to pull it to test it.

If you're uncomfortable reaching down to touch it, point an IR thermometer on the inlet and outlet. Temps will be the same when pump is engaged.

 

Thanks,Sean,

I used a stethoscope on the aux pump to determine that it is not running. I'd like to get at the connector to see if it is getting 12 volts, but that big top radiator hose is in the way. Looks like it should not be too hard to pull the pump if that is out of the way.

I've saved several bookmarks of instructions to change the brushes if that is the problem, but after finding that my IC pump was OK and the ECM was the problem I am not jumping to any conclusions. Looks like momma will have to drive the minivan for a while until I resolve the pump situation.

 

Phil, Have you tested the radiator efficiency?
IE how much lower is the water temp at the outlet as compared to the inlet

I would not get too hung up on the Aux pump till you solve the overheating.
Here in OZ we tend to pull the fuse for the Aux pump or in my case ive added a switch to disable it. It serves no purpose in hot climates to be pumping hot coolant while the AC is constantly on. Id enable the pump a max of 4 days per year

On the radiator the best way to test is with a dual temp meter. Insert a wire type thermocouple on the inlet and outlet. My meter will give the temps as well as a differential reading. Just remove the hoses , insert the wire probe, replace the hose and tighten up the clamp.

Its worth testing before pulling the radiator and backflushing or replacing

Cheers
34by151

 

If, as I think Phil has, you have drained the system then the auxiliary pump is rather important in topping the system back up.

Neither the IC pump nor the mechanical pump drains the coolant reservoir when going thru the refill/topping up process. Only the aux pump does that.

However a good idea of yours about switching off the aux pump during hot weather so long as all is well with the cooling system.

 

I looked back in my notes to see if I recorded the radiator temps read with my IR thermometer when I was checking it and checking the thermostat, but I did not write them down; guess I was satisfied that It was normal and did not write it down.

I thought the same thing about the Aux pump in hot weather - that it would not contribute to engine cooling unless you were pulling heat out of the cabin heater. I do need to fix it before cold weather comes and I do need to make sure it is not a leak source; hence next on the list.

I'll re check the radiator temps and write them down this time. One of the 100 mile drives included idling with the AC on for 20 minutes in 90F ambient at a drive-in, and it did not overheat then. It got up to 200 F plus or minus a degree or two (205 F is its normal max temp when it is behaving), and went back to 197F when we got back on the road. I'd expect a radiator efficiency problem would show up under those idling conditions.

I emailed our local auto tech school instructors to ask if they can do a coolant sniff test. They helped me out with an alignment so their students could see it done on a "furrin luxury car" and they were very capable guys with all the latest alignment equipment and saved me a couple hundred bucks. They even installed my two new tires and the new rear stabilizer bar links I had in the boot. Told me I had one wheel with excess lateral run out, though. I measured it at .050" later; those 19" chrome wheels are hard to find.

One good thing is that I've not gotten any air suspension warnings or the reservoir plausibility error code since I replaced the air compressor piston ring - thank you bagpipingandy.

 

Have you confirmed that the fan is operating normally when it should be? It could be failing intermittently.

 

Ive found hooking up a meter allows me to diagnose much easier

A dual input temp meter can usually be found cheaply
If you get the wire type thermocouples these can be inserted between a hose and flange

I also made an extension lead using cat6 and banana plugs/sockets
This way I can run the sensors with the meter in the cabin

The key is not the temps but the differential readings, IE the temp drop
Your looking for the temp creep. At the end of the day the output should be keeping up with the loads and your engine temp will never be lower than the output. You need to have this well below you operating temp or you will overheat. If your differential readings are low you cant expect the radiator to keep up.If the readings are high it indicates a blockage in the engine, water pump or thermostat.

To give you a rough guide.
My XJR would run around 95c (203f) and get as high as 118c (245f) on the track. Id pull back on the track with it over 110c and pull off if I could not get it down.

I changed to the low temp thermostat and I run around 83c (182f) most of the time peaking around 91c (195f) on the hottest days over 45c (113f)
Now on the track it never gets above 110c now matter how hard I push or for how long.

The factors your looking for are stopped with fans on and off and at speed under various load conditions. The main factors being flow speed of water and air. So its a lot easier with the engine up to temp and the thermostat open.

Also remember it's not until your reach 80kph (50mph) that the airflow from driving is greater than the airflow from fan on full when stopped

Id get some readings for you but its winter here in OZ. Average days are 22c
(72f) so it fairly cold here

As you have confirmed the thermostat operation and no leaks and head gasket, it comes down to flow. This may be from a blockage restricting flow or low flow. Restrictions may be in the radiator or the block. Low flow may be a bad water pump.

Cheers
34by151

 

The fans are working normally as far as I can tell. When it does get hot and the engine is shut down the fans continue to run for awhile - maybe 8 to 10 seconds?, or it could be longer

Where do you find a Dual input temp meter - some place like radio Shack? I see a couple on line for $250 to $350 and one on Amazon for $80 but I can't tell if the Amazon one uses small thermocouples - the others appear to have large probes. I see a couple of cheap Chinese ones on eBay in the $30 range that might do for a simple test.

It is interesting that you say "My XJR would run around 95c (203f) and get as high as 118c (245f)". When the dash temp gage of my SV8 was pegged and the warning light was on, my Ultragage would report up to 246 F but no higher, even when I had to keep driving for nearly a mile to find a safe place to pull over. The UG has a range up to 420 F so I wonder if the 246 F represents the upper limit of the Jag's temp sensor output.

I have confirmed thermostat operation, but not confirmed lack of coolant leaks or head gasket leaks yet. I just haven't found any but suspect there could be an operating temp coolant leak. Still, I agree it would be good to confirm radiator efficiency. What temp differential should I expect under normal (not track) driving conditions? Say 60 MPH in 80 F to 90 F ambient?

I heard back from the local auto tech instructor who asked about the water pump (which I have not changed) theorizing that if it has a plastic impeller it might be slipping after a certain distance and operating temp and reducing the cooling efficiency. Anyone know if an 06 has a plastic impeller?

 

I cannot speak directly about a 2006 XJR however when I replaced my 2005XJR water pump the new one had a metal impeller and the original had a plastic impeller.

I have still got the original and looking at it I cannot see how the plastic impeller would slip "some of the time".

If it is going to slip I would think it would slip all the time because of something going wrong with the drive shaft to plastic join which looks very solid on my original pump.

 

Water pump is somewhat of a big job so id eliminate the easy things first.

The temp meter will tell you if its the engine side (water pump/blockage) or radiator
If it turns out to be on the engine side id try flushing the system before replacing the pump

Re the meter this is what you are after for under $20 shipped

Digital Thermometer K Type Thermocouple Dual 2 Probe Sensor Metal 1300°C 2372°F | eBay

Cheers
34by151

 

Thanks, That meter said "does not ship to US", but I found the same thing from another seller who does - in fact there were a number who had the same thing coming from China - so I ordered one. I'll wait and try that before pulling the water pump.

Thanks Jackra_1 for the info on the impeller; good to know it doesn't look like it could be intermittent.