Ok I've replaced the water pump and had the radiator rodded by a radiator shop. Last weekend the expansion overflow tank sprung a leak, presumably because of better pressure in the system and I replaced that. The temp Guage is still erratic, it goes above N in minutes and sometimes comes down. My mechanic insists it's faulty Jag gauges however I still say the overall trend is for the Guage to rise despite its erratic behavior. I'm really hesitant to drive the car as the Guage tells me it's hot. Anything else I've missed? The whole cooling system is almost new. Would bleeding the system help. Would not bleeding it make it run hot? What else could it be, or is it really just a faulty guag?

 

lordlionheart,

You haven't said what year and what engine you've got?

How did you bleed the system when everything was replaced? The V12 is really sensitive to being bled in exactly the right procedure to ensure that the air is expunged.

Paul

 

<i>"My mechanic insists it's faulty Jag gauges however I still say the overall trend is for the Guage to rise despite its erratic behavior."</i>


Please find a new mechanic immediately. He is either lying or grossly incompetent or both.

I'm not kidding on this, and please don't ignore this advise. I've owned XJSs for 25 years, followed multiple forums, etc. -- the gauge is NEVER the issue.

Secondly, as per the wise post above, your mechanic likely didn't fill the system properly and you have air in the system.

 

1988 XJS Hess & Eisenhardt V12. There's the rub, I've been to 3 mechanics, including one who works on British cars, is a self proclaimed Jaguar expert. Been on forums for quite some years, which is how I knew about the bleeding. I guess I'll try that myself. What if that doesn't help?

 

<i>What if that doesn't help?</i>


Well, you will have eliminated the most likely cause, which will give the folks here a clue on where to steer your attention next.

Cross your fingers that will address your issue.

Good luck.

 

Buy an infrared thermometer if you don't already have one and start taking some readings to give an idea of how hot you are really running. At each thermo housing, upper and lower radiator hoses. Others probably can chime in on where to take readings.

But the proper bleeding procedure sounds like a good place to start.

 

lordlionheart,

Start with bleeding it properly although hopefully that is what the mechanic has done.

Have you got the proper bleeding procedure for the 5.3 V12? it's very important to do it the right way.

Paul

 

Your description of the gauge readings suggests air in the system....so you're on the right track. If it doesn't help, regroup!




FWIW, here's the Dwyer version of V12 cooling system bleeding:

There are different opinions on what works for filling and bleeding but most owners follow the same basic procedure. Here's the process I used on my '88 XJS V12 and a few others. It's not difficult, just messy.

Elevate the front of the car about 8" and then elevate the left front another 2-3" beyond that. Set the climate control for max heat so the heater valve opens.

Remove the bleeder plug from the left radiator tank. You'll see an access hole in the radiator upper mounting panel. The plug is some arcane size but you'll find something in your toolbox that fits.

Remove the caps from the expansion/header tank and from the filler pipe at the front of the engine....up there by the A/C compressor.

Add coolant/water to via the filler pipe until it reaches the bottom of the pipe. Start engine, set heater control to max heat. Let it run at idle until it warms up. Peek inside the filler pipe every minute or so and top up as needed.

When the engine gets warm increase the idle to about 1000-1200 rpm (a helper is helpful here...or just wedge a little something in the throttle linkage to hold it slightly open for a high idle.

Let 'er run and run. Give the upper radiator hoses a few squeezes now and again. Keep checking your coolant level in the filler pipe and top off as needed. Eventually you'll see some coolant coming out of the bleeder. That's good. Wait a while longer and (hopefully) you'll see coolant *really* pouring out of the bleeder. (How much? It's one of those "you'll know it when you see it" things..very messy)

When it's *really* pouring out of the bleeder hole, put the plug back in. Wear some gloves so you don't get scalded. If you can't get the plug back in thru all the gushing, shut off the engine and do it....but I like to leave the engine running if I can. Not worth getting burned, though.

Top off the coolant in the filler pipe...I go right to the top but some fill just to the bottom of the neck... add a quart or so to the expansion tank if you suspect it might be low, button everything up, and yer off to the races. If you've overfilled the excess will be pushed into the atmospheric tank mounted inside the fenderwell. If you've *really* overfilled the excess will exit the atmospheric tank and end up on the ground.

Lower the car and clean the driveway :-)

Cheers
DD

 

That's the exact one I have ................ and printed out and gave a copy to the mechanic when he installed the overflow tank.......I doubt he read it

 

Bled the cooling system and the needle climbed to H whilst doing it. Took about 15 minutes. I also noticed the heater didn't get hot when I turned it on. Heater core??? Just to recap I've replaced the water pump ( first leak), had the radiator rodded, replaced the expansion tank and it's still reading H?!?!

 

Assuming the bleeding was done correctly, I would then feel the rad hoses. If they do not feel as hot as what the gauge may indicate maybe the temp sending unit for the gauge is faulty. ( The one on the passenger side front cooling rail) An infrared temp reader will give you the temp at both thermostat housings. Compare these with the gauge. ( This also helps troubleshoot both stats). My brother once p/u one of these for ten bucks at Harbor Freight. If the heater core is plugged up then maybe your cooling passage ways are too? As for the heater feel your heater line as it comes off the block to the control valve, then after the control valve and finally the return line to the block on the drivers side. The first line would be hot, the second one hot too if the valve is open and the third pretty hot if the flow is passing through the core. If you suspect your passages have filled up with that white rust maybe a engine cooling flush would settle it down. Also a note to others - I have OFTEN seen large amounts of blockage between the rad and the AC evaporator rad to the point were quite some time was spent blowing out the cooling fins to remove this blockage. ( Rad out). (This usually blocks up the full bottom third of the rad's cooling fins). This should not apply in your case because you had the rad done. Hope this helps some, and by the way I found a cheap heater core valve with the correct tube sizing and vacuum operation from NAPA.

 

Thanks Superiorjag. I bought one of those infra- red heat guns and the radiator hoses are showing around 200 - 205 degrees. I've read 180 - 190 is preferred, would 205 be enough to shoot the temp all the way to the top? I have to admit I have no idea what the heater lines or heater valve looks like. I'll have to Google unless you have a pic?

Thanks for your help so far. I still think the car is getting hot despite all my efforts................ and $$$$

 

The heater core draws engine coolant from the rear passenger side cooling rail. Just look at the back of the passenger side intake manifold and you will find your typical heater hose. Mine passes right next to the tranny dipstick. About 10" toward the center of the firewall (from the transmission dipstick) there is a aluminum coloured roundish shaped valve about the size of a small orange. There is a small vacuum line going to the top of this valve. On the driver's side of this heater valve there is a short line turning 90 degrees into the firewall (heater matrix connection). That is it for the heater feed side description. The 'return to the block' line is found on the firewall, directly behind the drivers side valve cover, maybe 10" further to the drivers fender from the heater valve. It is easy to spot and feel or shoot w/ infrared. If this return line is cool in comparison to the passenger side line going to the heater valve, it would suggest coolant is not flowing through the heater core. I believe the vacuum actuated heater valve is open when no vacuum signal is present @ the heater valve. (open by default). The heater matrix sends a vacuum signal to the valve as required to pull the valve to the closed position. If you disconnect the vacuum line from the valve and attach another bit of hose to the valve you should be able to draw on the line and see the underside show movement, Plug the line with your tongue and the valve should stay in place until you release the vacuum. This would show the valve is operational and holding vacuum. As a point of interest, a larger vacuum line with a check valve in it (that comes from the passenger side intake manifold) should be readily spotted entering the cabin behind the passenger side valve cover, (or there abouts). This line feeds the heater matrix and should show manifold vacuum with the engine running. As for running at 205, I believe it should read closer to 180/190 depending on which thermostat you are running. If you haven't changed the stats yet be aware the stock thermostats have a small hole in them with a little 'tickle ball' thing that I believe is meant to help bleed air out of the system? I know the dealership should have them, but I think the ones I have purchased from after market stores did not have this feature. Also, is your auxiliary/ AC fan coming on at all? I am sure it should kick in right away if your A/C is turned on. It also turns on with a signal from a coolant temperature sensor, using a fan relay. If this is not turning on, disconnect the lead located about 10" from the fan motor and attach 12V and a ground line to the double connector to see if the fan is operational - (after checking the fuses). Does this help your temperature readings after running the fan for a while?