Hey Guys,

I am reaching now on my temp issues with my XJ6

So the temp gauge in the car was pegging but the car never really overheated (as in lost coolant). At first I thought it was a gauge problem in the car but decided to do due diligence and installed a actual temp gauge on the car to see exactly what the temps were. I had read the OE gauge jumps in steps from "you're good" to "you've already overheated"

So the temp gauge at idle ran over 200F and I was sure I had an issue. First thing I tried was pulling the thermostat and after I did that, the car ran cool as a cucumber for as long as I wanted it to.

Then I went and bought a new thermostat even though the one I pulled was not that old thinking it was just defective. Placed the new thermostat and the temps soared again above 200F. Pulled the new thermostat and the car stayed down in the 170-180 range at idle. Hmmmm, ok, leave the damn thermostat out and everything seemed to be fine. The OE gauge in the car was reconnected and the car never pegged the needle again until just recently.

My wife was driving the car and said the temp gauge pegged again in the car so now I am confused. Here is what I have right now.

1) Car had a new temp sensor (for gauge) and new thermostat - no issues
2) when car first started pegging I replaced the temp sensor - no change
3) changed the thermostat - no change
4) monitored engine temps and with thermostat in car gets over 200F at idle. With thermostat removed it is 170-180 at idle.
5) car ran fine with thermostat removed - for a while.
6) car is still exhibiting a pegged temp gauge once in a while. Most of the time it sits below the middle bar.

I am clueless as to what could cause rapid changes in engine temp like this? So I was wondering if it was possible that the waterpump could be intermittently seizing or spinning causing the car to suddenly get hot. Has anyone ever heard of such a thing?

Thinking about possible causes for this kinda ruled out some things like the radiator. I am thinking if there was clogging or corrosion somewhere in the system, the car would get hot and stay hot. It wouldn't run totally normal and then within seconds jump to hot?

Bernie

 

Bernie,
I'm not a mechanic.
You live in the desert - is it hot there at the moment - do you need a lower temp thermostat?
Is your radiator buggered? It may not be coping with Las Vegas.
I had a new aluminium one made, for less cost that a plastic/metal core genuine Jag one from the UK.
just my thoughts

 

All valid thoughts.
However, currently there is no thermostat in the car at all and it is still doing it.

Also, those results I found were with the car at idle and fans running so I am baffled as to how the thing can suddenly run its temp up?

 

Couple of thoughts from down here, and being a regular in Vegas, i also know ts HOT at the moment.

The thermostat restricts the flow of the coolant thru the radiator to allow it to cool as designed. NO stat and the coolant will flow tooooo quick and not cool sufficiently, and eventually this wil result in overheating. UNLESS the radiator is partly clogged, then removing the stat will run it cooler, coz the blockage is slowing the coolant, but it is only a temp fix at any stretch of reality.

200F is not boiling, we know that, then add the increase in boiling point due to the pressure cap (I forget the formular now of ??deg/PSI pressure), and then the fact these engines are designed to run at about 198F due to emission requirements, I wonder if you have a gauge issue more than a car issue??.

My 3.2 X300 had a wavering gauge way back, and I replaced the water pump, coz I could, and the issue turned out to be a dud pressure cap. Had the same with 2 of the V12's, simple $10 cap caused all sorts of grief.

Out on a limb, but is the integrity of the front pulley rubber lamination all good??. If it is dying, the main drive pulley MAY be slipping, thus the drive oomph is lost.

 

Grant's points are very valid. I don't think 200 degrees (93 degrees in real money) is excessively hot and not enough to peg a temp gauge. I suspect there is an intermittent fault on the wiring for the temp sender (possibly the plug?).

The sender just varies resistance to ground with temperature - high resistance = high temperature. So if there was an intermittent loss of ground to the gauge it would read that as very high temp. Try wiggling wires for the sender and see if you can replicate the fault - you can do that with the engine cold.

You say that the temp goes from normal to pegged in seconds - i really can't see how the actual engine temp would do that, but a faulty electrical connection could.

 

Ok,

After driving the car in various conditions the temp can get as high as 230F. The thermostat has been removed altogether and the fans are bridged to run constantly. The current temps in Vegas are 105 - 108F so pretty hot here. This means my temp gauge was probably correct all along and since it is not a graduated gauge it probably hits a certain temp and then bounces right to the redline as I have seen in others posts.

I am contemplating what I can do with the cooling system to get this under control. Of course I think a system flush should be done, the spider coolant hose shows some corrosion around a couple of fittings so I will swap that out. I don't know the condition of the radiator so I can have that looked into. Then of course a refill and adding some Water Wetter to improve heat transfer. Outside of those things, not sure what else?

Replace the pressure cap on the surge tank
Replace the waterpump (is there a better one than stock)
Bigger radiator (probably cost prohibitive)
Better / Faster fans?

Just not sure where to go from here?
Maybe I will find a problem with the setup as I go through it but for the time being the Jag is limited to straight line runs with no stop and go traffic. I don't want to damage this motor.

 

Hey Bernie, my temp guage runs just below the middle mark from about 185F to somewhere above 210F actuals as reported via Torque App for Android. I looked down at it yesterday and found it pegged...past the red on the post!!! Yikes. Dialed up Torque and it was reporting 249F. I was stuck in stop-n-go traffic in the middle lane of a crowded thoroughfare. I got to 257F complete with percolating sounds and steam coming out of the left bonnet seam before I got to a place I could shut it down. Percolating noises were the coolant being forced past the pressure cap. (Grant, I believe it is one degree F rise in BP per psi - sorry all, I have no idea what that is in degrees sillygrade per bar!)


Anyway, you didn't mention what your thermostat setting was (seem to recall 195 is std with 185 commonly available, or vice-versa.) Also, you say the fans are bridged to run constantly - do you mean TSB 14-06 has been performed which brings both fans on low speed (series connection) any time the key is on? This doesn't get you to high-speed, only preps the fans so they don't blow the fuses when hi-speed is commanded. Hi-speed (parallel connection) fan is commanded by the triplex a/c switch when high-side pressure passes 22 bar (320 psi or so) If I recall, you are experiencing some A/C issues...maybe you are never hitting the 22-bar trip? Radiator switch commands low-speed at 85C and hi-speed at 100C - so at 230F you should have high-fan-speed due to the radiator switch even if your climate control is shut off. I can tell you from very recent experience that 40 mph or so at 98F ambient will cool the 4.0L with the fans off. Alternatively, sitting still at idle with them off in the same conditions will get you to 250+ in short order....

 

My suggestions:

Remove the radiator, get it professionally cleaned, inside and out. Being an alloy/plastic unit, that may not be viable, so a new unit is the best.

Flush the engine block as best you can whilst teh radiator is out. Replace any hoses that are suspect.

The water pump is the water pump, and the stock unit is just fine. If it is not leaking leave it be. Perhaps remove it form the back mounting plate and ensure the impellor is intact (they do corrode without the correct coolant), and also ensure the apposing face on the backing housing is not corroded away, which would give way too much impellor clearence, and very litlle coolant flow.

Refit a cooler spec thermosta. Mine ran an 89c, and in our 47c summers the cooling system was just sweet.

The fan operation needs to sorted and confirmed that hi speed fans are available. The sender switch in the LH lower edge of the radiator may be culprit.

 

Thanks for the detailed response! Hope your car is OK after seriously overheating?
I removed my thermostat altogether in the hopes that the increase in flow might help the car run cooler. So its definitely not a thermostat problem. Yes, I have placed a jumper on the AC connector in the engine bay so that the fans come on as soon as the key is turned. I think my fans are triggering to high speed but I never really noticed it while the car sits and idles.

The car can idle for a long long time without getting much past 210F but when I drive the car it slowly but surely hits the 230F mark in stop and go traffic. It will cool down to a tick over 200 if I am casually and constantly moving.

I ordered a couple of things like the spider hose and the pressure cap just because I have no idea how old those parts are. The hose is definitely showing corrosion around a couple of connections so while I am at the job, I can clean that up. The radiator will get a flush when I get it pulled out to make sure I have adequate flow through it.

The weather is going to start to cool off here in the coming weeks at least by Vegas standards. It will surely help with the cars temps but that's when I need to go for it while its cool and easy to work outside. Its pretty much constantly above 105F here now.

Cheers
Bernie

 

Much appreciated.

Why do you think the radiator cannot be flushed?

 

Bernie,

These alloy/plastic radiators have the plastic tanks "crimped" to the core, and a seal in between. Down here the availabilty of said seals is not good, and the "recrimping" is also so-so, then comes the cost.

Some outfits flush radiators with the tanks ON, and claim all sorts of % success. I am very old school, and tanks OFF is the only way I would clean any radiator that is suspected of having clogging issues. The crud inside gets like concrete, and any solvent strong enough to dissolve that will dissolve the alloy core for sure.

New radiators are not that expensive in the big scheme. I just got one for the S, and $365AUS was fair enough in my opinion. I saw them cheaper in the States, but shipping killed it cold.

 

Razorboy, on an X300 Jaguar the water pump are mechanical and the belt is the one driving this part, there can never be interval operation unless the belt breaks then the water pump does not function. The internal part of the waterpump consist of an impeller and water/mechanical seal. as you said there was no coolant leak then there is nothing wrong with your water pump. Make sure the radiator is fully functional with no blockage. Engine temperature increases may be due to internal combustion parts anomaly. (check your engine timing)

Follow the instruction of Grant Francis, he is absolutely correct when it comes to cleaning radiator core,

or you may send it to a radiator dialysis which is mostly available in most radiator shops. It includes cleaning the engine block core where water passages of engine and cylinder head's are. They do reverse flow

 

Whilst having the radiator checked / flushed / replaced makes sense, I would be inclined to bottom out the high speed fan issue first. In the sort of temperatures you are experiencing, in stop start traffic conditions with A/C on, the fans should be operating in high speed, The difference in heat rejection from low speed is not insignificant, and as you are operating in the upper ranges of the systems capabilities, every bit of heat removed from the coolant is important. Once you get behind the curve, and heat generated gets ahead of heat rejected, things can escalate quite quickly.
For what it is worth, you should be able to detect the fans running at high speed from inside the car, as they are an order of magnitude noisier than when in low speed.

 

taking out the thermostat is a big mistake, the intention of the thermostat was meant to regulate the water from circulating, making it stay a bit longer on the radiator core and for the temperature to cool down. with thermostat taken off there is very chance for the water temperature to cool down by the radiator.

 

Water Pump internal component/parts

 

How hard is it to replace the waterpump? I don't do a lot anymore but I need one and my garage wants 700 to do it. Also, I need a steering rack.

 

Water pump on an x300 isn't hard at all. Like with most things engine wise, a lot more needs to get removed on an XJR as opposed to an XJ6.

For an XJ6 all you really have to remove are the drive belts, alternator/water pump and AC. Once those are removed, there are the bolts the hold the water pump to the water pump 'housing' itself. The hardest part of the job is probably adjusting the alternator to remove the belt. When I replaced the water pump on my XJR, I used red rtv gasket maker and waited 24 hours for it to cure before I refilled it with coolant.

Does the 700 your shop quoted you include the steering rack and labor for that? Or 700 just for water pump and labor?

 

The 700 was for a new waterpump (about $400) and labor. I found a rebuilt from Coventry West for under $100 12 month warranty and unlimited miles, so I am going to do that. The steering rack is around 2K .

 

2K ??? Time to find a new shop!

 

The majority of the cost is the steering rack, what should i pay and where would you suggest getting one? The shop is good and he is willing to work with me. He will use whatever parts I source?