Ok, it looks like an ECU issue for the Radiator Fan no workie, but let me 'splain first.......

I just bought the Jag and love it. But I noticed the coolant temp never got too high. Looking at typical Jag issue, I immediately focus on rubbish coolant (green + orange = crap) and the Thermostat. The originally GREEN coolant was entirely flushed and replaced with the correct orange coolant and the Thermostat was replaced.

Coolant temp is now smack-dab in the middle of the indicator, but I am over-flowing the Overflow Tank when the car gets warm and fans are not turning on. *** Note, indicator very rarely goes above halfway. I checked the Temp Sensor and resistance checked good.

So now, for poops and grins I am focusing on the Radiator Fan electronics. All fuses are good. Fan are checked good by removing the Radiator Fan Relay and using a "jumper" on the connector. On a personal note, I am an engineer and will personally eviscerate the chap who thought the Radiator Relay location was a good idea. Anyways, I replaced the Relay next. Still no dice.

Now, I focused on the operation of the Radiator Relay. The Fan output wires tested fine to the fans, but the other wires are wonky. The two "signal" wires are always +12VDC (no on/off PWM signal at all) and the ground is ****-poor. I found the grounding stud location and clean it up to get a MUCH BETTER continuity to ground. However, now I am stuck with the "signal" wires that do not appear to be alternating.

Does anyone have an idea of how to induce a test with the ECU and Radiator Fans to get the signal wires working? I tried shorting the Coolant Temp Sensor, but that did not force the Fans on.

Thoughts? Ideas? Questions? Clarification?

Thanks in advance for any help!

 

Well good-ish news. Thanks to Brutal in another post, the Radiator Fans do indeed work with A/C on.

So, my big question is now "Why is the overflow tank pissing coolant (at the drain port) as the engine gets too hot?" Shouldn't the fans be turning on by this point?

*Note: Coolant temp hardly ever goes above halfway.

*Note: After a short time driving, the hot coolant expands and heads out the drain port of the Overflow tank. Then I get a low coolant light.

 

The symptoms you describe is one of excessive pressure in the coolant jacket when engine is at normal temperature. I had this syndrome on both a Rover V8 (which was originally a small Buick engine), and a 1980 Jaguar XJ6 4.2.

It was found to be a blown head gasket where the location of the failure allowed combustion gases into the coolant jacket, pressurising it and pushing out the coolant via the overflow. With modern test equipment, a check can now be made which can detect combustion gases in the coolant so you can know one way or the other, without taking the head off.

Of course it may be something else !

 

Modern equipment at a repair shop or something I can check with? Compression tester?

Let's tackle this sucker head on. Thanks for the help.

 

There is a Turky baister looking tool that has a chamber you fill with the test fluid and then run the car to temp and suck the air from the resivior into the baister and if the test fluid changes from blue to yellow it indicate there are exhaust gasses on you coolant. I believe it is called combustion leak tester. Snapon sells one for 80$ part number gdct16.

 

I have also heard of people mixing up locations of where the bleed hoses connect to the resivior, and it will do wierd things with the resivior.

 

Haha! Now we are talking. The transmission shop I bought the car from replaced the transmission (thank god) and did a bunch of minor work in the engine bay (spark plugs, injectors, rubber tubes, etc). ADDITIONALLY, I am getting a P0171 and P0174 failures that will not stay cleared..... so funky bleed hoses are a possibility.

Much investigation needs to be done. Keep the ideas coming. Thanks a ton.

BTW, Anyone have a good picture of proper hose locations? XJ8 4.0 Sport?

 

Update: Before, it looked like somewhere around the FILL TANK was leaking. The Jag was pissing a relatively small amount of coolant. So, I filled up the coolant (only about a 1/4 gallon of water) and did my best Jeremy Clarkson impression on a local highway to try and replicate the leaking......... everything ran perfect. I feel this tale is not done yet.

Update on the P0171 and P0174: Found two injectors unseated. One reseated fine and the other will probably need replaced.


Thanks everyone, this board is great. I hope i can help contribute to it as much as you guys do!
Cheers

 

Thanks for your update and good to see your problems were fixed
I have just noticed that your car should be X308 assuming model year and moved it into the proper place as well

Happy safe driving

 

You are past this point: it is very important to not allow the engine to overheat in the Jag V8 -- they do have a habit of needing head gaskets after this occurs.

On the fill/expansion tank the small hoses should cross -- this looks incorrect but the hose going to the overflow tank in the drivers front fender is not the end connection on the fill tank. it is the middle one.


Also - the temp gauge will show in the normal range over a very wide temperature range. By the time it shows outside the normal range -- the engine is overheating. It is not set up to be a progressive gauge.


You want to make sure the plastic cover over the thermostat is not damaged -- many replace this with the metal one from the XJR -- this is a known problem.

Also ..many times the incorrect thermostat is installed because the OE is a bit $$ .......... People trying to save 10 bucks cause $$$$ of damage.


It is so easy ti get the correct part and fluid -- but so often it is not used

 

If there is a picture available, then if anyone could post it, the assistance would be very helpful. I am QUITE sure the hoses do NOT cross. This may be the issue.


Good to know. I may install my own temporary Data Acquisition system to monitor temp and just to be safe. Mmmmmm, Arduino


Everything else looks kosher. Thermostat FYI

 

If you go onto the recent post "need some XJ advise" and go to the link of the car he is looking at -- then go to the pictures -- you will see one of the motor showing the fill tank and the hoses.




That is not an OE thermostat:

I have no idea of the fit or how it will operate -- how it will flow. Thermostats are a part that I absolutely never use anything other than the OE part .. never. Over the years I have seen so many failures regarding this little part that I don't play around with it. They are important to the proper operation of the system -- it is not just an "on / off" operation.

 

Yes, the Top hose (Overflow Tank hose) is installed correctly. The two hoses that do NOT cross on my Jag are the other two small hoses below the Overflow Tank Hose.

Unfortunately the S/C cover-plate is covering the routing of the other two hoses. Thanks for trying, I do appreciate the help.

 

I guess I don't understand -- the other small hoses go to the top of the thermostat and the radiator -- they are to remove any air stuck in the system - the supercharged cars get an additional one. I think the close one goes to the radiator.

 

Yes, those two hoses. As long as those hoses do not have to cross or twist or anything, then I am good to go. I assume as long as the Thermostat and Radiator hoses are connected below the Overflow Tank Hose, then life should be good.

Again, I have a feeling something is not quite right, maybe a clogged Hose(s), maybe something else. I have all of my engine panels removed so next time she leaks, I will better be able to pinpoint the problem.

*Note: Funny thing, during the "Jeremy Clarkson Testing", no leaks and the Radiator Fans turned on as advertised.

BTW, is there a good place online to get an OEM Thermostat. I would much rather be safe than sorry.

 

Quick update: Aluminum Thermostat housing weld bead bad. New Aluminum housing on order and when I get my TIG welder, I will get the old one fixed.

No other leaks..... yet.

 

'nother update, and I am hoping someone has a coolant schematic laying around for an XJ8. As mentioned before, the Thermostat housing has bad weld and a minor leak; part is on order and will easily get replaced.

My OTHER fun coolant leak is behind the engine near the firewall. I have a larger hose coming from the center of the engine to a T-fitting. One end of the T-fitting goes to the Coolant Fill Tank. Now the other end of the T-fitting goes to the Throttle Body. Consider me ignorant, but why does the coolant line go to the Throttle Body? Anti-ice feature? How significant is this Anti-ice feature?

Thanks for any education and help,
Cheers,
Sean

 

Woot! All is fixed. Replaced Thermostat housing and no more leaking. I think the rear leak I had before was actually splash from the housing leaking and draining on the top of the engine.

Reseated Injectors correctly and ensured Air Filter housing had a thorough seal, all checks great.

Thanks for the help everyone!