XJ XJ8 / XJR ( X308 ) 1997 - 2003

water temperature gauge always in the middle.

 
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Old 03-12-2019, 06:03 AM
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Default water temperature gauge always in the middle.

hello i have a question my xj8 water temperature gauge needle is always in the middle is that normal? or there might be a problem in the cooling system? shouldnt the needle stay below the middle?

 
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Old 03-12-2019, 06:40 AM
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Nope, with these cars, there is actually quite a range of temps that are considered "normal" and the needle stays dead center. However, when it DOES go up, it's because you're already in trouble. It's much safer to run either a RealGauge ( XK8 / XKR / XJ RealGauge - TheJagWrangler ) or an app like Torque with a bluetooth OBDII adapter that will allow you to see actual values and not just a needle. I forget at what point it is that the needle finally moves up past center, but once it does, it's because you're on the verge of overheating and unless you catch it quick, it can be too late.
 
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Old 03-12-2019, 08:10 AM
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Originally Posted by CharlzO View Post
Nope, with these cars, there is actually quite a range of temps that are considered "normal" and the needle stays dead center. However, when it DOES go up, it's because you're already in trouble. It's much safer to run either a RealGauge ( XK8 / XKR / XJ RealGauge - TheJagWrangler ) or an app like Torque with a bluetooth OBDII adapter that will allow you to see actual values and not just a needle. I forget at what point it is that the needle finally moves up past center, but once it does, it's because you're on the verge of overheating and unless you catch it quick, it can be too late.
thanks for useful info. any idea to improve the cooling system? was thinking to changeing the OEM electric fans to high performance one any advices?
 
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Old 03-12-2019, 08:30 AM
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Originally Posted by mobile1 View Post
thanks for useful info. any idea to improve the cooling system? was thinking to changeing the OEM electric fans to high performance one any advices?
you could install a thermostat that opens at a cooler temperature (84C instead of 87C).
If the engine is supercharged, the supercharger intercooler pump can be exchanged with a more powerful one from Bosch that is used in some Mercs too.
 
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Old 03-12-2019, 10:49 AM
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Originally Posted by mobile1 View Post
thanks for useful info. any idea to improve the cooling system? was thinking to changeing the OEM electric fans to high performance one any advices?
If your temperature guage is showing mid way on the guage there is probably nothing wrong with your cooling system.

Originally Posted by iDon View Post
you could install a thermostat that opens at a cooler temperature (84C instead of 87C)..
The thermostat only controls the amount of time it takes for the engine to get to operating temperature, changing to a different temperature setting does not affect the running temperature, that is controlled by water flow and radiator size.

.

 
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Old 03-12-2019, 11:05 AM
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Mine settles just a tad below center. Normal. Gets there after about 2 miles of driving.
 
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Old 03-12-2019, 12:03 PM
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If you have an OBD II reader that reports engine temperature, plug it in and keep it plugged in while you drive. It will show you what your actual temp is. As Carny Kid noted, you probably are running the right temp (but to be sure, keep the radiator clean, change the coolant on schedule, make sure your hoses are new and tight, keep an eye on the belt for age and heat damage, first sign of weeping, replace the water pump, thermostat, TST housing, crossover pipe and sensor); range for thermostat does not control how hot the engine gets, just when it opens. Jag engineers have tried to have it open as soon as possible to limit pollution -- trust them.

There are lots of threads on this forum concerning over heating in the 4.0 engines -- read up on it if you are concerned. Just for future reference, it would be useful if you add your vehicle info (yr, model, engine) and your location in your signature and data blocks. Why? Some interesting effects for cooling systems in cold climates (like hoses that pop off suddenly) and overheating in supercharged units. But overheating will destroy your engine; it is worth watching closely in all cars that are old!!
 
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Old 03-12-2019, 05:29 PM
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Originally Posted by Carnival Kid View Post
If your temperature guage is showing mid way on the guage there is probably nothing wrong with your cooling system.



The thermostat only controls the amount of time it takes for the engine to get to operating temperature, changing to a different temperature setting does not affect the running temperature, that is controlled by water flow and radiator size.

.
I did quick search but didn't find any high performance aluminium radiator for my xj8. do you know any after market brand that manes high performance radiator?
 
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Old 03-12-2019, 05:35 PM
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Originally Posted by Jhartz View Post
If you have an OBD II reader that reports engine temperature, plug it in and keep it plugged in while you drive. It will show you what your actual temp is. As Carny Kid noted, you probably are running the right temp (but to be sure, keep the radiator clean, change the coolant on schedule, make sure your hoses are new and tight, keep an eye on the belt for age and heat damage, first sign of weeping, replace the water pump, thermostat, TST housing, crossover pipe and sensor); range for thermostat does not control how hot the engine gets, just when it opens. Jag engineers have tried to have it open as soon as possible to limit pollution -- trust them.

There are lots of threads on this forum concerning over heating in the 4.0 engines -- read up on it if you are concerned. Just for future reference, it would be useful if you add your vehicle info (yr, model, engine) and your location in your signature and data blocks. Why? Some interesting effects for cooling systems in cold climates (like hoses that pop off suddenly) and overheating in supercharged units. But overheating will destroy your engine; it is worth watching closely in all cars that are old!!
the hoses looks fine in good shape . will get an obd reader
it's 3.2 I believe it has steel cylinder wall not nickasil .
​​​​
 
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Old 03-12-2019, 06:05 PM
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Why would you want a "High Performance" radiator? The radiator type and size is carefully designed to suit the everyday driving of the vehicle in a wide range of climates. If you wanted to replace it as a cautionary preventative maintenance I would buy a new OEM replacement. They are not cheap by any means, but I don't think you can get an aftermarket one any cheaper, in fact they seems to be even more expensive in most cases. . https://landrovermerriamparts.com/pa...iagram=4721045
 
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Old 03-13-2019, 03:58 AM
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Originally Posted by Carnival Kid View Post
Why would you want a "High Performance" radiator? The radiator type and size is carefully designed to suit the everyday driving of the vehicle in a wide range of climates. If you wanted to replace it as a cautionary preventative maintenance I would buy a new OEM replacement. They are not cheap by any means, but I don't think you can get an aftermarket one any cheaper, in fact they seems to be even more expensive in most cases. . https://landrovermerriamparts.com/pa...iagram=4721045
I think it's better to bring down the temperature little bit. to avlia head gasket issues but sounds like it's better to keep everything as is
 
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Old 03-13-2019, 04:22 AM
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Not sure why you think Jaguar didn’t do their homework when they designed the cooling system for the car?
They set the thermostat temp to get the best results out of the engine. A cooler thermo will cause the engine to run at or about that temp. Head gasket issues only generally arise through lack of maintenance or mechanical failure of a part, not because the engine is running at its design temperature.
 
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Old 03-13-2019, 06:20 AM
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Middle is fine.
I actually design engine temperature sensors for a living. (Not Jag)
As others have mentioned, the sensor output is not necessarily linear with temperature. There is a "sweet spot" in the middle of the gauge, where the temperature does not appear to change, even though the temperature of the engine may change slightly. It is carefully and deliberately designed that way.
What is the point of an accurate gauge, when it is largely dependent on the thermostat, which has not really changed since 1934?
 
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Old 03-13-2019, 07:52 AM
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Originally Posted by Robman25 View Post
Not sure why you think Jaguar didnt do their homework when they designed the cooling system for the car?
They set the thermostat temp to get the best results out of the engine. A cooler thermo will cause the engine to run at or about that temp. Head gasket issues only generally arise through lack of maintenance or mechanical failure of a part, not because the engine is running at its design temperature.
I'm new to jaguar cars and V8 engines so thought it might be an issue but now I know it's designed like that
 
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Old 03-13-2019, 07:52 AM
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Originally Posted by DAVESPACEBAT View Post
Middle is fine.
I actually design engine temperature sensors for a living. (Not Jag)
As others have mentioned, the sensor output is not necessarily linear with temperature. There is a "sweet spot" in the middle of the gauge, where the temperature does not appear to change, even though the temperature of the engine may change slightly. It is carefully and deliberately designed that way.
What is the point of an accurate gauge, when it is largely dependent on the thermostat, which has not really changed since 1934?
thanks for info
 
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Old 03-13-2019, 10:30 AM
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Just to add, the Jag temp gauge is electronic and it has circuitry programmed to deliberately keep the gauge needle in the middle over a wide engine temp range, form about 70C to somewhere around 110C. Why was this done? - to prevent customers complaining that sometimes the gauge needle is above the middle, "my engine is overheating" (when it is not a t all) etc. The Jag engine is designed to operate between about 85C to more than 100C with no issues at all. The fast radiator fan speed is set to come on at 97.5C, meaning that the engine temp will go over 100C before it starts coming down (I know this because I have installed an additional accurate digital engine temp gauge). This, allowed by design, temp range of 85C to more than 100C, would cause the needle of an "honest" temp gauge to fluctuate quite a lot and get owners worried so, make a "lying" gauge - peg the needle to the middle electronically.

Jaguar did the same thing on XJ12-s with the oil pressure gauge - pegged the needle at a "healthy" oil pressure, for pressures below a certain point, electronically because many customers were complaining during the warranty period that the oil pressure at idle was too low. It was actually normal with these engines and, since Jaguar did not want to bother explaining to each customer, they found an easy solution ("no problem sir, it's just a faulty gauge; we will replace it").
 
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