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XJS 1975 - 1996 3.6 4.0 5.3 6.0

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  #1  
Old 07-24-2012, 02:03 PM
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Default overheating...again

So almost a year ago my car was overheating BAD and blew a hose out. I replaced both thermostats and the hose. Recently i have replaced all hoses and the water pump and it is now overheating again.

The main fan spins as much as i want it to, so i know it is bad. The car heats up quickly because of this but maintains temp for a while so its not bad daily driving and stays at good temps. However after idling too long it obviously goes up due to the fan but curiously it overheats on the highway after long driving as well.

The car tends to go between N and H and sit for a while then rapidly jump back down to below the N. This can't have much to do( or can it?) with the fan because above 35-45mph most cars don't even need fans to cool the radiator. Also annoyingly this is a high compression engine so if the car gets hot from highway driving it is difficult to start again.

Any ideas?? Maybe the thermostats went out again? Not a very hard job and neither is the clutch for the fan but still im wondering before taking the thermostats out and testing them( i also hate making gaskets). Any other possibilities?

Last edited by sidescrollin; 07-24-2012 at 02:10 PM.
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Old 07-24-2012, 02:12 PM
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for more information. On the highway it will drive for a good hour or two before it goes about the N. Its curious that it suddenly bumps between high and back down to below the N but after a while it mostly stay up there. Maybe my gauge is off and this is the stats coming on and off?? I dont really think so because the stats should maintain a temp range finer than that.
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Old 07-24-2012, 02:17 PM
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Quote:
Originally Posted by sidescrollin View Post
The main fan spins as much as i want it to, so i know it is bad. The car heats up quickly because of this but maintains temp for a while so its not bad daily driving and stays at good temps. However after idling too long it obviously goes up due to the fan but curiously it overheats on the highway after long driving as well.


Yeah, sounds like a weak fan clutch. Also, is your aux elect fan kicking in?




Quote:
The car tends to go between N and H and sit for a while then rapidly jump back down to below the N. This can't have much to do( or can it?) with the fan


Air pocket, most likely. Bleed the system again.




Quote:
because above 35-45mph most cars don't even need fans to cool the radiator.


I'm one of the minority that doesn't always believe that's the case :-)




Quote:
Also annoyingly this is a high compression engine so if the car gets hot from highway driving it is difficult to start again.


Sounds more like a weak starter IMHO


Cheers
DD
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Old 07-24-2012, 02:24 PM
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thanks for all the help doug.


When can i test for the fan kicking on? It doesn't seem to come on but all the fuses and relays are good and it spins freely with my hand. Doesn't come on with the car up to temp with the a/c on or off.


Im hoping its mostly due to this blown *** clutch which will be an easy fix sometimes this car just behaves differently than other cars ive experience so i always like asking for someone else's opinion before tackling an issue.

i can safely say i haven't properly bleed the system from what i remember, i think i just ran coolant through it. Valve is top left side of radiator right??


im also on the fence with the fan thing...especially with this big hot engine....
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Old 07-24-2012, 06:29 PM
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Quote:
Originally Posted by sidescrollin View Post
The car tends to go between N and H and sit for a while then rapidly jump back down to below the N.
This is the exact symptom mine had and after replacing thermostats etc I decided to bite the bullet and have the radiator recored and voila problem fixed. Above 70km/h the engine sat on the thermostats - you cold watch the temperature go up and down (well below the N) as the thermostats cycled.

In the 88 model the aux fan was not hooked up to the AC, mine does not come on with AC either.
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Old 07-24-2012, 06:41 PM
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You must have the barrel type gauges on your '88?

It has always been my impression that you would never come close to reaching the H, and you'd drop a seat about 3/4 of the way there... Is it pegging on the H?

Cheers,

- Will
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Old 07-24-2012, 06:59 PM
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Do you have jiggle pin stats, and are they oriented properly?

An improperly functioning fan can impede ariflow at speed by acting as though you're putting a big pie plate over the rad. It can block airflow instead of moving it if it's not working correctly. Fix the fan then let's see what happens.
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Old 07-24-2012, 07:19 PM
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Download Kirby's book and do ALL the cooling system repairs. Remove the radiator and have a shop clean and check it. If it is questionable have it recored. Clean all the debris from the condenser fins and from between the condenser and radiator. The foam surrounding the radiator is most likely completely gone so you need to replace that. Install new hoses, all of them. Make sure you have the correct thermostats with the jiggle pins and the bypass block off discs. Make sure the fan shroud is installed and the rubber flaps actually work. If not make new flaps.

Also do you have the lower air dam installed? If not this will cause, at higher speeds, air to bypass the lower grill opening.

The aux. electric fan should come on with the A/C and when the temp gets pretty hot. There is a separate switch for this.

The cooling system on these cars is sufficient to cool them. However there is no extra cooling capacity so everything needs to be up to par.

Usually what happens is there are a bunch of small issues that add up to an overheating or hot running engine. Lower temp thermostats is not a fix but many seem to think so.

Doug, I will not argue with you but you are certainly in the minority about fans at speed. Dare I say wrong? Nah you are too good of a guy to be wrong....
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Old 07-24-2012, 07:58 PM
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Quote:
Originally Posted by macboots View Post
You must have the barrel type gauges on your '88?

It has always been my impression that you would never come close to reaching the H, and you'd drop a seat about 3/4 of the way there... Is it pegging on the H?

Cheers,

- Will

It is true about the only thing that will kill a Jag V12 is overheating, BUT I have seen a twin turbo V12 race car come in spewing coolant everywhere and temps sky high on numerous occasions and never a dropped valve seat. I can also say with my car it ran 6000km across Australia consistently over temp, gauge over N with some times 2/3rds to H and no dropped valve seat. These engines are very study.

Now the only thing both of these cars have is electronic ignition NO distributor advance this maybe the savoir???

Slight overheating is more than likely not going to cause you a dropped valve seat, it is an indication that something is wrong and it is advisable to correct it ASAP.

Make sure the distributor advance mechanism is functioning (The book procedure is to use a dab of engine oil) and the cooling system is working correctly.

I have been thinking about your problem and I would tackle this in this order.

1. a) Fix the mechanical fan clutch and get the aux fan working. The aux fan should come on when the radiator outlet temp reaches about 90C (somewhat - I am at work so dont have my book handy). Get this working and the car should idle in traffic without overheating if the radiator is OK.
b) Check for debris between the AC condenser and radiator.
c) Check the dissy advance to make sure it is not binding or stuck.

2. Last if this does not work I would pull the radiator and have it looked at by a shop.
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Old 07-24-2012, 08:06 PM
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Quote:
Originally Posted by Greg Edge View Post
The cooling system on these cars is sufficient to cool them. However there is no extra cooling capacity so everything needs to be up to par.


Exactly!



Quote:
Usually what happens is there are a bunch of small issues that add up to an overheating or hot running engine. Lower temp thermostats is not a fix but many seem to think so.

Exactly !



Quote:
Doug, I will not argue with you but you are certainly in the minority about fans at speed. Dare I say wrong? Nah you are too good of a guy to be wrong....
<grin>

Over the years I've had a couple cars (non-Jag) where a weak fan clutch caused overheating at highway speed.

FWIW, both were GM cars, both used for trailer pulling, and the overheating occured in 90-100F ambient conditions at 60+ mph

<shrug>


Cheers
DD
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Old 07-24-2012, 09:55 PM
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I don't know if this will help or not, but when I replaced my engine I found the fan had a crack in it. I removed and replaced it with an electric fan with a radiator sensor, and wired it in series to the original aux fan temp sensor. Now the large electric fan comes on at one temp, and if it gets a little hotter both fans come on. Because it has it's own power supply it can run even with the key in the off position.

My temp gauge doesn't ever touch the bottom of the N now!
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Old 07-25-2012, 11:42 AM
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Quote:
Originally Posted by macboots View Post
You must have the barrel type gauges on your '88?

It has always been my impression that you would never come close to reaching the H, and you'd drop a seat about 3/4 of the way there... Is it pegging on the H?

Cheers,

- Will
just to clear this up with everyone.....this is a huge myth surrounding the jaguar v12. CAN the car drop a seat from overheating?? Yes, certainly.

Is the jaguar V12 as easily damaged from being overheated as everyone says?? No.


There was a period of time where i had no money to fix my car but HAD to drive it to work (no bus option). I have had this car inbetween the N and H numerous times and actually pegged on the H numerous times without it even blowing the radiator caps. The V12 is a very robust engine.

This is no reason to ignore your car overheating but people seriously act as if the car even hints at topping the N the engine will blow up.
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Old 07-25-2012, 11:45 AM
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15 miles yesterday and it ran fine. Just got another job. Will bleed the system, maybe check the thermostats and replace the clutch once i get some money.

Its an easy job but maybe ill do a simple write up in case there is ever a new-comer who doesn't know exactly where everything is or how to get the fan off since it is a bit fiddly.
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Old 07-25-2012, 11:46 AM
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thanks for the help btw didnt really think of the fan at the other side of the radiator as reducing air flow but i guess it is acting as a damn and limiting the total airflow through the radiator!
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Old 07-25-2012, 12:30 PM
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Quote:
Originally Posted by sidescrollin View Post
just to clear this up with everyone.....this is a huge myth surrounding the jaguar v12. CAN the car drop a seat from overheating?? Yes, certainly.

Is the jaguar V12 as easily damaged from being overheated as everyone says?? No.


There was a period of time where i had no money to fix my car but HAD to drive it to work (no bus option). I have had this car inbetween the N and H numerous times and actually pegged on the H numerous times without it even blowing the radiator caps. The V12 is a very robust engine.

This is no reason to ignore your car overheating but people seriously act as if the car even hints at topping the N the engine will blow up.


I agree.

And I disagree :-)

The dropping-valve-seat thing is too prevalent to be mentioned together with the word "myth". It DOES happen, as you say and we all know. Lord knows how many Jag V12s have been scrapped (or lumped) as a result.

But, yes, there's a high degree of paranoia out there...perhaps too high in some cases...but at the end of the day it's a good paranoia compared to the possible consequences :-)

And remember it's not simply overheating that causes the dropped valve seats. The damage can occur at normal coolant temps if there are air pockets in the cylinder heads. This is what makes proper bleeding and clean radiators so important.

Just my two cents


Cheers
DD
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Old 07-25-2012, 02:22 PM
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don't even go there see above I don't know what this is? Too old see twitter
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My auxiliary fan was not working either and after looking at various websites I traced the fault to the fact that the relay was missing completely - some idiot had taken it out and not replaced it.
The relay (on my '86 V12) is in the front left corner (looking from the back of the car) of the engine bay, buried below a pile of wiring behind the radiator and below the headlight pod.
It is a red relay and should be easily available.
I fitted a new one and the fan now kicks in correctly and runs for a minute or 2 after switching off.
Car still overheats though so further investigation is required.
Steve
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Old 07-25-2012, 07:43 PM
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Quote:
Originally Posted by Doug View Post
Exactly!






Exactly !





<grin>

Over the years I've had a couple cars (non-Jag) where a weak fan clutch caused overheating at highway speed.

FWIW, both were GM cars, both used for trailer pulling, and the overheating occured in 90-100F ambient conditions at 60+ mph

<shrug>


Cheers
DD
I believe you. I have seen many things that are "not possible" over the years in the car business. But it is probably because it was a GM product.
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Old 07-25-2012, 08:17 PM
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Quote:
Originally Posted by sidescrollin View Post
15 miles yesterday and it ran fine. Just got another job. Will bleed the system, maybe check the thermostats and replace the clutch once i get some money.

Its an easy job but maybe ill do a simple write up in case there is ever a new-comer who doesn't know exactly where everything is or how to get the fan off since it is a bit fiddly.

These fans look very simmilar to the fans I have installed from and Aussie Ford Falcon. You could wire them up with a simple switch so they are manually operated, just don't forget to switch them on when needed.

TYC 620280 Radiator & Condenser Cooling Fan Assembly New with Lifetime Warranty | eBay

Best of all they are cheap.
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Old 07-26-2012, 01:09 AM
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Quote:
Originally Posted by warrjon View Post
These fans look very simmilar to the fans I have installed from and Aussie Ford Falcon. You could wire them up with a simple switch so they are manually operated, just don't forget to switch them on when needed.

TYC 620280 Radiator & Condenser Cooling Fan Assembly New with Lifetime Warranty | eBay

Best of all they are cheap.
without actually checking dimensions..this looks like an awesome find!! ive always wanted to just buy some electric fans from ebay or something but have been afraid of dealing with my shroud....at least theres something to work with here!
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Old 07-26-2012, 01:40 AM
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With lifetime warranty no less.

For reference, if the ad disappears sometime in the future, one fitment is a 2002 Ford Windstar. $78.

Other Part Number: XF2Z 8C607 AB
Manufacturer Part Number: 620280
Interchange Part Number: FO3115111

Last edited by plums; 07-26-2012 at 01:42 AM.
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Old 07-26-2012, 01:40 AM
 
 
 
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aux, bleed, cooling, doesnt, engine, fan, highway, hott, isnt, jaguar, overheated, overheating, sdden, system, xjs



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