I'm curious if anyone else has monitored their coolant temp (on a scan tool) while driving on the highway. I had issues with my cooling system in the past, so I occasionally watched it with the scan tool just to check up on things.

What I noticed about this car, the coolant temp will stay 197 F during the winter. But in the summer, cruising on the highway the temp will go higher (200-205). I realize that the thermostat "starts opening at 190 and is fully open at 210", but I've never seen another car that increased temperature when it has 75 mph ram air blowing over the radiator.

I know it's perfectly normal for coolant to go to 205 F when idling through traffic, but on all other cars I've checked it usually drops back down to 195 and stays there once moving again.

Debating whether this is normal for this car, or if I should try another thermostat and see if it regulates the temperature better.

 

Could the fact that in winter the air conditioner is doing more heating and therefore removing more heat from the coolant, and less in the summer, be a factor ?

 

It all depends on which engine you have

I have the 4.2 s/c with a low temp thermostat
Normal temp is 91c and it will rarely vary on the road.

With that said I live in the tropics so a cold in winter is +25c but summer can get into the 40c+

The only time I get higher temps is on the track and I can push the temps to around 95c

The difference with the thermostat change is I was pushing the temps to 110c on the track with the oem thermostat. Also it takes a lot longer to warm up it gets to +60 fairly quick then slows down it takes about 15mins of driving to get above 80c and reaches 90c after about 30mins.

Cheers
34by151

 

It's the 4.2 N/A with the OE thermostat. The tstat housing is not broken internally, that was replaced already.

I regularly see 95 C (205 F) in summer driving even on the highway, but never above that.

 

With all due respect, this illustrates the (non)problems created by accessing otherwise hidden information.

There's nothing wrong with the car. The thermostat is doing it's job perfectly.

 

Hmm... I don't think I agree with the basis of your argument. Just because Jaguar used a temperature gauge that provides minimal useful information, doesn't mean that coolant temperature is some special "hidden" information.

Yes, it may be working just fine, but I will conclude that myself after I hear other people tell me their cars normally run 200-210 F on the highway.

 

The temperatures you've quoted are typical of most modern cars. The range you've noted (197 to 205) indicates a thermostat working normally.

 

Suppose it's not normal. It would have to be something like lack of coolant flow. Broken water pump?

 

I agree that 205 is not an abnormal temperature, but I'm still surprised to see it running at that (or hotter) at a steady cruising speed. In my experience, a car with a 195 tstat will sit right at 195 when you're cruising on the highway. Then if you exit, sit in traffic, the temp will creep up to 205-210 (or whatever the fan setpoint is) before it starts dropping back down. 200-205 may be normal for this car, but I feel like something is a bit odd if I'm seeing increasing temperatures when I have plenty of airflow over the radiator to keep things cool.

I don't think the water pump is broken, though I suppose it's possible. I thought they had gone to metal impellers by this year. I've flushed the radiator previously (off the car) and flow seemed fine. I would bet on a slightly faulty tstat, maybe this particular one regulates a bit hotter than another might. It is an OEM tstat with only 40k miles on it.

I suppose if I'm really curious I can buy a new tstat and try it on the car, see if there's any difference in regulating temperature. Otherwise I'd have to assume like Mikey said that this is the normal operating temp for this engine setup.

 

You're presuming that the car has plenty of airflow. I'm not sure that all cars always have 'plenty' under all conditions.

While it's logical to assume that there's more airflow across a rad at highway speeds than while stopped, the volume of heat being created also changes. An undersized rad might be adequate in the city but not big enough for highway duty.

The science/art of balanced cooling systems is far more complex than imagined.

 

I'm going to assume this car has pretty decent aerodynamics, and with the undertray and baffles in place it should create a low pressure zone that pulls air through the radiator at cruising speed.

I was watching the coolant temp on my way home today. 80F ambient, ac set to 72F. Cruising at 70 mph the coolant temp was 195F. I gave it a little gas to pass a car, dropped to 5th gear for 3 seconds to get to 75 mph (rpm went from 2000 to 2300), the temp jumped immediately to 200 F. Then slowly decreased back to 195F after 15-20 seconds. That makes no sense to me, unless there's some poor coolant flow within the engine, and somehow the sensor got a burst of hot coolant when it rev'd 300 rpm? No idea there.

Got off the highway, sat at a stoplight it rose to 205 F. Driving 35-45 mph in moving traffic the temps stayed at 200-205.

I guess those numbers are okay--looking back at my Cadillac FSM, fans go on low speed at 220F, high speed at 230F (if not using a/c), and I've never seen over 210F in this car. Maybe it is operating normally... but that's why I was asking if anyone else sees the same temps on their vehicle.

 

To be honest an increase of 5°F (a shade less than 3°C) is pretty small.

I don't think you'd pay much attention to it if it were on an analog dial, a proper one with a continuous range, say 65°C/150°F to 125°C/250°F.

If it were a proper dial with 270 degree angle dial min-to-max, 150-to-250 °F, then an increase of 5°F is a change in needle angle of 14 degrees, that's less than half the angle between the numerals on a clock face.

On a 120-ish degree angle dial, like the one on the X350, you'd hardly notice it.

 

Try your cruising test w/o your AC on. The AC will draw more heat around the radiator.

 

It is really hard to find an used radiator even from the scrapyard without paying hundreds of euros

So what I will do next is I will put the hoses off and connect the cooler to a pump which is normally used to pump the water from the river into the garden (well the flowers need water and the water from the river is for free ).

I will pump clean warm water with a bit of citric resolver through the radiator.
Then I will see whether the water at the output is clean or not and how much water comes out of the outlet.

I will keep you all informed =]

 

Saving my pennies for aluminum radiators for mine.

 

Woo5ie was on the right track in post 37👍 I didn’t realize there are multiple parts to the thermostat.

In any case, very happy to hear you found the problem. 👏👏👏
Was surely aggravating to resolve but now you a well sorted cooling system for the future

 

I want to refresh the topic. I have a problem with my thermostat, but strangely in the opposite direction. In a traffic jam, the temperature on the gauges reaches 90 degrees. A computer reading confirms the operating temperature is normal. When I drive above 75 mph the temperature drops to about 82 degrees Celsius. A year ago I replaced a new radiator and expansion fluid tank. Now I have replaced the thermostat. First, the replacement and the readings were the same. Later I replaced it with the original thermostat. The readings were also the same. I replaced the coolant, but it didn't change anything. Do you have any ideas for my case?

 

Thermostat range of control is not perfect, but when mine has gone WORSE than that relatively narrow spread, applying presure/vacuum tester & vacuum charger has found it a "warning".... of trapped air concealing coolant loss - or incomplete charging.

Suggest some detective work on that possibility, most especially, as you have recently done cooling system work.

Low cost for the easy-to-use test gear. High cost if the engine is damaged. == Readily justifiable spend.

 

Do you mean to measure the pressure in the cylinder system? Do you mean to measure the pressure in the refrigeration system? The engine works perfectly. I'm on a journey right now. Fuel consumption is normal. No fluids were lost. normal. No fluids were lost.

 

Fluid may not have been "lost" but that is not the same and identical to being 100% certain the system was fully filled to begin with.

5.0 AJ133 fitted to the Rover is worse as to air bleeding than the 4.2 in the Jaguar, (I have one of each), but both are subject to the trapped air problem, even with three bleed points.

It was the 2005 XJ8-L that was driving me bonkers with the sudden DROP in temps on 75 MPH interstate over about a 70 mile trip. Not until a day when it suddenly jumped UP from just above the blue 'cold' range to red overheat range did I twig to what was afoot. Once I got the AIR out of it, it became apparent that the coolant actually WAS low, and had been since the previous antifreeze change - fortunately very recent at that time.

As to the tools and method I researched and adopted AFTERWARDS:

Pressure and vaccum test on the cooling system, and each held for a significant period of time, can help detect even VERY slow leakage. Annnnnd - what we are looking for that relates to our mystery cooling - trapped air. Cheap kit, that one, but identifying a problem is not the same as resolving the problem.

A vacuum charging system additionally can be used to introduce coolant without the hassle of trapped air arising in the first place.

Common item in modern dealership & indy garages. More spend, but not that much more. Annnnd it can do the job of the cheaper one. Had I but bought it FIRST, I'd have saved a few bob.

My one, not terribly expensive, is operated by venturi effect off a small 'pancake' air compressor I was otherwise using to drive nails. Easier to get it near the vehicle than the big compressor, and the kit doesn't need much air to do its job anyway.

"The usual suspects" carry these, usually made in China,.

https://www.ebay.com/itm/354990966486

...but .... I don't do this work for any but my own two vehicles, and not very often, even so, ergo they have proven more than good enough.