I have been screwing with my coolant system for several months now and it is still not right. First there was the reoccurring 'low coolant' warning and then . . . last October, driving up one of my local mountains, the coolant hose from the thermostat housing to the lower radiator blew off and I got to ride in the cab of a big green flatbed tow truck.

The low coolant problem was the radiator cross over pipe that had a slow leak from rotting plastic just inside the hose. Pressure test kit finally showed that one up.

Since I had to open the coolant system I decided that it was time to change out the plastic thermostat housing to the aluminum version. Been there before on the previous car so that wasn't such a big deal other than the infamous rear bolts on the housing. I have a new bent wrench in case anyone would like to use it.

Tight Wad Tom had replaced the thermostat 3-4 years or so ago so rather than replace it again I tested it in a pan of water on the stove with an IR temp gauge verifying that it quickly and repetitively opened at the prescribed 183 degrees. TWT also replaced the Zerez G05 with Peak Universal on sale.

Ok, new cross over pipe with included temperature sensor, new thermostat housing, new radiator hoses, new coolant after some serious flushing and everything is fine . . . . Until the first serious cold snap when I noticed the radiator fans running in 20*F weather with the AC off. Of course, the dash temp gauge was happily dead center of good. I was out of town and only had the TORQUE Android app to verify temperature. It was reading 200+ degrees in cold ambient temperature. Coventry West quickly shipped a replacement cross over pipe to replace the suspect temp sensor. Installed that and sorta ignored the issue due to bad weather for the past two+ months while the car sat in the garage attached to a battery tender.

Beautiful 60* day today and I decided to install the TheJagWrangler's RealGauge that I had purchased during the earlier issues and not installed.

Guess what . . . on the test drive to verify the RealGauge operation with the Torque app I am still seeing very high temperatures. At 50 mph, which sorta overwhelms the question of fan operation, with 60* ambient temperature the Torque app displayed 212* confirmed by an upscale reading of the new and improved instrument panel gauge. Not into the red but getting close. The fans were running.

Now what? I guess my entertainment tomorrow will be replacement of the thermostat and flushing and back flushing of the coolant system.

Guess the water pump is going to come off for inspection also. Don't remember many failures of later pumps due to the disappearing pump vanes. This one is original 13 years old with 74k miles. Only other thing that comes to mind is mixing of antifreeze has clogged up the coolant system. I understand the OAT and HOAT coolant gel discussion but the fluid in the reservoir show no signs of being other than expected.

Lesson #1: The Jaguar temperature idiot gauge can get you into trouble if not destroy your engine.

Comments and commiserations appreciated.

 

That temp does seem high. My '01 only hits that range in traffic in 95F or above temperatures.

Not sure about the Zerez coolant, but I assume you checked for compatibility. Also assume you verified the thermostat was installed notch up facing the right way.

The water pump is easy to change and given your effort ($$) so far, I'd spring for a new thermostat. A lot cheaper than the engine.

Has the radiator been checked?

 

Checked in with Advance AP for a water pump and found $98 for a Chinese made new one. Ebay has them for $26 with free shipping for a Chinese pump including gasket and 'O' ring.

Anyone had a problem with the cheap pumps?

Guess that after 74k miles I might as well change the serpentine belt also since it has to come off.

TWT

 

I noticed my engine was not getting above 185 deg while moving so I replaced the thermostat. It now runs at 195-197, even in near freezing weather, and when waiting for a light it goes to about 205 and the fan comes on. This is confirmed by both the Realgauge and the Ultrgauge.

When I put the thermostats in a pan of water to compare, they both began opening at about 183 and were fully open at about 195. Confusing. I would swap them again but I'm lazy and it's messy with the radiator drain location.

I would like to replace that stupid drain plug with a petcock to which I can attach a hose to avoid getting coolant all over the car and the floor when I drain the radiator, but I'm not sure of the thread size. I'll have to check that next time I have to drain.

 

+1



The 'giggle pin' (item 1) assists air to bleed from the system and does allow some coolant flow in the event of a sticking thermostat.

Graham

 

With the aluminum housing I have the thermostat only goes in with the correct orientation.

 

On the ones I've done there's nothing to prevent the Thermostat being rotated left or right from the giggle pin in the "12:00 o'clock" position.



Has the design been changed on later Thermostat Towers?

Graham

 

As indicated in the title to this thread while the current running temperature seems high I was unsure if it was incorrect. Mine is running at that 195-197 range. My thermostat on the stove was beginning to open at 183 and was fully open within seconds at about 187 as measured by an IR thermostat.

The temp sensor is located at the very hottest point on the engine just as the coolant leaves the head through the thermostat so maybe the 195-197 range should be expected.

As mentioned, the thermostat housing was recently replaced and while I cannot remember if alternate positions were possible I was aware of the jiggle valve position and installed it up.

 

Tom,

Just one small input for you. I ran G05 for a few years in my '01, then later reverted to Jaguar-spec coolant. There was never any problem with things getting gummed up ... saw no evidence of such a thing at all.

 

On my 03 with all new crap on all the cooling sys short of the radiator at speed 50 or more I see on my torque app about 190 give or take 5 degree depending on tempos outside, if I have to slow down, etc.

 

At 50 mph, 212 F is definitely at least 10 degrees F over what I would expect for normal cruising temperature. Seems like a bad thermostat, water pump or an inefficient radiator, considering the work you have done already.

A new thermostat and at least a water pump inspection makes sense. Another thing you might check for is if there is evidence of lime scale in the radiator. A previous owner or mechanic might have filled the system with hard tap water.

Glad RealGauge and Torque are agreeing.

 

Yeah, I know it has been over a month since this thread started.

But it was a beautiful day today and I had to take the car out for a run. I have a replacement thermostat and pump in hand but still wonder if one or both are the problem.

Today, with 70* temperatures the TORQUE app and JagWrangler's RealGauge both reading 96*C/204*F with fans running but not significant at 65mph.

First, the displayed temp wanders around far more than I have experienced with a rebuild of the V8 Volvo coolant system. The Ford/Volvo system stays withing +- 2* F of the 180 degree thermostat. The Jaguar is wandering from 92*C/192*F to 100*C/212*F for no apparent reason.

Now the confusion factor . . . my IR temp gauge measuring the brass body of the temp sensor/varistor reads 87*C/188*F and the head temp is reading 97*C/207*F. That better matches the thermostat rating which I stove tested OK.

Remember, I changed the crossover pipe which came with the sensor included. I returned the first one because it seemed to be reading too high and keeping the fans on in single digits outside temps. It might be that the reproduction crossover pipe/temp sensor that Coventry West is selling has the wrong sensor installed.

Discussed with CW and they say they have sold hundreds of the aftermarket pipes/sensors and I am the only one that returned it for replacement. I responded that only someone using the TORQUE app or RealGauge and having a IR gauge would ever see the issue. Certainly not reading the Jaguar StupidGauge.

Now, here comes the questions . . . anyone know the specifications of the the varistor temp/resistance graph of the correct sensor for this car?

Better to try a local auto parts store sensor before new water pump/thermostat?

 

See page 30 for the resistance chart : http://www.jagrepair.com/images/TSB/...rd%20Start.pdf

AJ26 and AJ27 engines use the same sensor.

 

anywhere in the 195-205 range should be considered normal for any modern alum engine IMHO. 220 and I'm getting pretty nervous. 225-230 and I'm calling the rollback for a ride.
Have you pulled the plastic upper radiator retainer piece off and checked for debris between the A/C condenser and radiator core?

Russ

 

Russ, the problem is that IR gauge says everything is good, the TORQUE app and RealGauge say that it is not.

Steve,

Perfect! Now all I have to do is plot actual resistance against temp for the sensor supplied by Coventry West. What you want to bet that they will not match?

Sensor out, heat gun, IR temp gauge, VOM.

The problem I have is that the current sensor keeps the fans running all the time.

 

Please post your results. Thanks.

 

Anything is possible. If you can read the Denso sensor number off of the sensor itself on your pipe, I'd be happy to compare it to a unit that we got straight from Jaguar to make sure it's the exact same one.

That was one of my first thoughts, too, when the salesman you've been talking to told me about this. As I'm sure you know, most people are not exactly pro-active and are content as long as the gauge stays right where it always does...or as long as steam isn't coming out of the engine bay

Pending the results of your resistance tests, we do have an aftermarket supplier for that crossover pipe sensor; we could certainly provide you with one if you feel that the sensors you've been getting aren't providing accurate readings.

 

Had a lot of cooling system issues with a 2000 XK8. The two primaries that came to the surface - I found that the only sensor that would work with my top hose cross over pipe was from a 1999 supercharged and more importantly found that the wire to the left fan connection was missing some of the insulation which resulted in corrosion and proper fan running. The latter fixed my issue with blowing hoses. I also noticed that the idiot light (temp gauge) now fluctuates slightly below the 1/2 point where as before it held steady at slightly above 1/2.

 

Today I got to the temperature vs. resistance measurements of the temp sensor included in the cross over pipe replacement.

Test disclaimer: The meat thermometer is not a calibrated testing device nor is the DVOM.

The sensor provided is marked Denso 179700-0220 which appears to be the replacement part specified for the Jaguar plus most Ford, Mazda and several other car brands. The in-car readings of this sensor are consistent with those experienced with the first sensor therefore you could draw the conclusion that the measurements would be similar.

Using a meat thermometer and a DVOM I determined the following:

Temp
C/F . . . . Expected . . . . .Measured
70/158 . . . 435 ohms . . . 400 ohms
80/176 . . . 320 . . . . . . . . 290
90/194 . . . 250 . . . . . . . . 220

The expected ohms are those in the Technical Bulletin Steve provided above.

Unable to measure 100C/212F because I am 1650 feet above sea level and water boils at 209F degrees corrected for altitude and current barometric pressure and my thermometer only goes to 200F.

It would appear that the sensor is off by about 9-11% which is consistent with the amount that my IR temp gauge, another less than lab quality instrument, reads compared to the TORQUE app and JagRangler's RealGauge

Now what?

Unless there is another Denso sensor with slightly different specifications or an OEM Jaguar sensor provides resistances that match their Tech Bulletin my fans will run all the time and my RealGauge will hover just under the alarm point. And what will happen when Summer gets here and it is 40 degrees warmer outside.

 

Tom,

A quick-and-dirty solution comes to mind:

Your sensor is reading about 30 ohms low in all the cases you checked. How about just putting a 30 ohm resistor in series with it?