Hi all:
I have a 2000 XK8 no supercharger. I keep blowing major cooling system hoses both the large in-feed and return, off their connections. The temp gauge on the instrument panel never reads more than 1/2. I have replaced the temp sensor unit on the in-feed (top) hose and have replaced the thermostat and coolant cap. All with no success. I have never seen the twin cooling fans come on, even with the temp gauge at 1/2 or with the AC on and engine at full operating temp. Also noticed that the problem seems to occur at the end of a drive after slowing down or stopping.
Any input greatly appreciated.
Thanks

 

The cooling fans are supposed to come on when the A/C is on, so you just need to check the fuses and solenoids.

The temp. gauge is designed to read accurately to mid scale. At higher temps it remains at center until about 235 F, then jumps to red, at which time it may be too late to avoid damage. I wonder why the pressure cap doesn't vent to the overflow tank before the hoses blow off.

 

Thanks for the info. I have checked fuses but not solenoids. Cannot understand the cap issue. Second cap same results.

 

The other issue that I hate to bring up is a leaking head gasket. I have never used one but there is a test kit sold to check for exhaust gasses in the coolant.

Coolant system over pressure brings up thoughts of thermostat, reservoir cap, head gasket sorta in that order.

 

I thought if it were a head gasket that it would get hot with any car, real hot from the get go, no driving around then when you park it the hoses blow off.

 

It would depend on where the head gasket leak is. If the coolant isn't superheating and the hoses are still blowing off the only place that much pressure could come from if otherwise is a head gasket. And yes its strange that the cap isn't venting it. It could be the thermostat but you would think it would overheat rather quickly if it was.
You could have pressure test done on the cooling system. If the pressure leaks down with no signs of it leaking externally it could be the head gasket.

I had a '47 Buick straight 8 with only 12k miles on it that did that. And it wouldn't show as overheating on the gauge. But it would blow off the radiator cap or hose after driving then slowing down. Turned out they forgot to drill the coolant return holes in the head so the water was going into the head and couldn't get back out until it got so hot it blew out as steam back from where it came. That explained the low miles on the car and it was amazing they got that many miles on it.


Dave

 

Don't get crazy, and think worse case. Fix your fans first, you KNOW they are not working properly, there are two relays I believe on driver side lower down. Also while the cap maybe bad you may also have overfill hose plugged, the overfill is in drivers side wheel well front of tire, remove plastic well protectors and you'll see it (turn wheel all way right) Think Occam's Razor, simplest solution is often the right solution.

 

Thanks sounds like good info. I do know that the car had damage on the driver side front.

 

I would expect to see evidence of anti freeze in the oil if I had a blown head gasket??
There is none.?

 

Not necessarily. I had a VW diesel that blew a gasket with no signs other than blowing hoses off.

 

Finally have had the time to get back to work on the JAG. (A little side trip to look at a barn find, parked for 30 years, 1958 MGA out west. It's coming home. Like I needed another toy.) Any way - Not a head gasket on the Jag. Compression test was as close to perfect as could be expected for something with 68K miles (all within 15% of each other. 110 - 130) Still baffled. New stat, new reservoir cap, new temp sensor, great compression, water circulating great (both hoses hot at operating temp), temp gauge never goes above 1/2 way point, coolant circulating in reservoir, nothing venting to overflow because reservoir never gets that full. Fans still not coming on with AC on/off and engine at operating temp. Fuses and relays (Any idea how many relays there are? I found two.) are OK. No OBD faults recording. Any suggestions for what to look for next? Take fans out and bench test? Maybe just carry a few extra gallons of premix coolant in the trunk and drive it!

 

As I said in post#2, if the cooling cap is functioning properly, the coolant will flow to the overflow tank when the engine heats up and you will not have excess pressure.
Turn the A/C on and the fans should run, or just let it idle and eventually they should come on.
The temp gauge will not go above mid point until the engine gets to about 230 deg, that's how it's designed.
Pressure caps are not expensive, get a new one.

 

I would describe 110 psi and 15% spread a little out of specs but the issue seems to have evolved into the fans not coming on at all. The AC requires a fan to run never mind the system temp.

Looks like time to start tracing the little electrons. Fan relays located down by the fans.

I just got set up with the Android Torque Pro app on a smart phone. Along with a $10 OBDII to Bluetooth converter it will read the actual reported degrees Celsius at the data port. Saw the converter on Black Friday sale on line for $2.12 this morning.

 

Use the attached oneline diagram and check the power to the fans and remember you have a radiator fan control module.

As for it overheating it sounds like you have a circulation problem and I would be checking the water pump and for a collapsed hose. You may also be looking at the possibility of the coolant jelling that is caused by mixing incompatible coolants together.

http://www.jagrepair.com/images/Auto.../jagxk2000.pdf
Page 22 for relay layout Page 23 for radiator control relay module
Page 93 Fig 04.3 – 04.6 for the cooling fan wiring diagram

 

Thanks - I took your advice on the cap and am on my second new one. You are correct - they are not that expensive. When the first new one did not correct the problem I took it back as a possible defective and replaced it.

 

Gus:
Great link. Thanks.
As to the overheating, I am only seeing evidence of excess pressure (possible from overheating but the temp gauge never goes above 1/2 way even immediately after it has blown a hose off. I have a couple of sensors that are in my basket at SNG but will use the diagram to see if I have the correct OE part numbers and not a dufrappis sensor for something else.

 

I am thinking that the water is not moving resulting is the overheating. If the water pump is not working or a collapsed hose could cause this. The gauge not moving is not a big indicator because of the wide range from normal to over heating is a wide range on the stick gauge.

 

The instrument panel gauge is not telling you anything.

I had the large hose to the bottom of the radiator blow off for no apparent reason other than it was 12 years old as was the plastic thermostat housing that it was clamped to. I could find nothing wrong that a new hose, a new aluminum housing and a couple clamps did not fix.

You really need to know the coolant system temp and pressure. An IR gauge will tell the temp to a degree. I just called O'Riley and they said that their coolant system test tool kit will measure system pressure although I have never used it that way. Incidentally, I just had to replace both temp sensors on the V8 Volvo. Neither was anything other than open hot or cold. Note that they fail in a manner so as to not cause further problems ie: the fans stay on all the time rather than not at all.

May I suggest if you plan on changing the temp sensor mounted in the cross over pipe that you order a new pipe as they are common failure points and come with a sensor.

I drove through Talking Rock twice today. If I can help, holler.

 

Test Point:
Thanks for the input. I have already replaced the cross over pipe temp sensor. Interesting point on the sensor - my Vin is definitely for a 2000 XK8 yet the only replacement sensor that matched the one removed was for a 1999 XK8 Turbo Charged. The plastic cross over hose connections looks to be in newer condition (wondering if a 1999 sensor may not be correctly talking to a 2000 to be part of the issue) I noticed yesterday that the radiator, just to the touch, was hot top to bottom at operating temperature. I have OBD software and connections to my laptop and intend to check "real temp" with that as soon as I can get the fans running. Please stop if you see a silver XK8 beside route 5 with steam rolling out from under the hood.

 

The real question is what is the actual coolant temp vs the sensor/OBD port reported temp.

I should have my new sensor in tomorrow and will report the resistance at various temps as measured with an IR meter at the sensor vs the OBD reported temps.