Hi All,

Some of you may recall posts by me a year or so ago when I was whinging about my 2001 XJR overheating. Well, it seems I still have problems but am unsure what or where

This is what has been done:

• New radiator
• New waterpump
• New thermostat
• New [second-hand] fan assembly
• Auto transmission serviced

On warm days 30*C / 86*F the car still seems to get very hot when sitting in crawling/bumper-to-bumper traffic, ie. climbs to 112*C / 234*F

Turning off AC and turning on heater full (not desirable in hot weather) cools her down to a respectable sub 100*C / 212*F temperature.

Fans kick in at the correct temp and stay on after I stop the car (when very hot).

What I notice first when the car is overheating is how the auto transmission starts to change. The car starts to "thump" into gear when moving off at very slow temperatures and seems very sluggish. In one of my other threads I've been advised the transmission is designed to do this when overheating...but it feels horrible.

No auto transmission overheating message appears (if there is such a message).

The dummy temp gauge in the vehicle doesn't move over half.

I'm really at a loss as to what to do next. This just doesn't seem right and I get very concerned when driving.

I never have a problem with this when highway driving - I recently drove over 1,000km / 620 miles in 12 hours in very hot weather with no problems at all. In cooler weather I don't have this problem.

It seems to me the fans are just not cooling the car sufficiently when the vehicle isn't moving.

For any of you that haven't fallen asleep at this point, thanks for letting me rant and waffle. I feel a little better now

Troy.

 

Perhaps you have a bad thermostat? There was just a member who had a similar issue, but when he broke out his thermostat, it was in backwards via the previous owner. Not that yours may be in wrong, but it may simply be a bad one where it isn't opening all the way? Its the cheapest fix, and quickly done.

 

...already done! I also checked that the fans kicked in when the car reached the correct temperature.

 

Since you give an actual temperature reading, what are you using to monitor temps?

When it does start to overheat, do your fans kick into high speed?

 

I'm using an OBD2 scanner. It's been a while since I last tested the fans - I did this last year before replacing the radiator and waterpump.

I will recheck the exact temperatures today.

When the fans first kick-in (in the late 90*C range) should they immediately go into high speed?

 

Oh, c'mon now, you took the air out my balloon....lol.
Something just doesn't seem to be flowing correctly. Have you burped the plug on the S/C? Are you sure the lines on the intercooler are run correctly (if they were removed)? Have you checked the 2 lines under the S/C?

 

Sorry man, I really don't want to get pulled up for something simple like a thermostat!

I believe the S/C would have been burped sufficiently - it's been serviced twice (including a major) by two very well known Jaguar service centres too.

I've never touched anything to do with the intercooler or "2 lines" under the S/C

I just wonder how to tell if the radiator fans are actually running efficiently enough to cool when I'm not moving/crawling.

 

The radiator fans should always be spinning together when they're on. When the car approaches slightly over operating temp, they kick on in "slow" mode, electrically in series, and when the car is very hot, and/or if the aircon compressor is engaged, both fans will spin at max speed, electrically in parallel. They should push enough air to where you should feel the hot rad air blowing from under the car when the hood is closed.

Could it be something as simple as a gunked up radiator?

How do the fans feel when you spin them by hand? Bad bearings? They should spin pretty quickly even in low speed mode.

 

Do these models have an aux coolant pump (as well as the SC pump) as mine has?

Might the (old/current) water pump have broken up?

You look to be doing the right things. (Not much consolation, granted.)

 

The car has had a new radiator put in...so nice unclogged fins

Fans seem to be running nicely, when the AC is on they spin fast/hard. The AC is always on when the car gets too hot. The temp rises very quickly when the AC is on - a few degrees every couple of mins (and drops at the same rate when the AC is off).

 

I'd be looking at the auxiliary pump which sits above the left hand wheel arch in the engine bay, it may not be functioning correctly. A good flush of the system would probably help too, as previously said it may be some gunk. It may have become dislodged and blocked something.

It sounds like the same issues I was having when my thermostat failed whilst driving home from France a few years ago, only the temp gauge went up to the max when stuck in traffic.

 

Can the auxiliary pump affect the cooling system that much? Nobody has ever mentioned this to me before

Troy.

 

The supercharger pump?

From the engine repair course:

 

I'm thinking aux not SC pump.

Besides, SC pump fail tends to throw codes.

 

@jagv8 @stu1986

I'm guessing it's not the auxiliary pump - when I turn the heater on it blasts out super-hot air (and the coolant temp drops almost instantly). Is that a fair assumption?

From people's comments/suggestions, it is fair to say a failure of the aux OR SC pump would [potentially] cause the engine coolant to get too hot?

 

EscapedApe, you replaced the engine radiator, have you checked the S/C radiator?

 

Hey Highhorse,

No I haven't replaced it. These parts cost a fortune over here (not sure about costs in the US/UK). Replacing the radiator, water pump, thermostat and fan assembly has so far cost me $6k ....so I'm very cautious about what to change/investigate next

 

$6K!!! Is that in yen??? OMG!!

 

Dittos....HOLY SMOLY!

You should be able to get that boiled out if it needs it. A whole lot cheaper than replacement.

 

SC pump fail does not cause coolant overheat as they're almost separate coolant circuits. You also do tend to get a code.