proper coolant temp

#1
What should the ideal coolant temp be for the 3.5 V8 on S.U.'s? I'm currently running an 88c thermostat (a spare from my first Range Rover)- temp of the intake manifold at thermo housing taken with an infrared thermometer is 85-86c after a 10 mile run. Needle on the gauge sits right on the "5". I know this has been discussed before.... what's the general opinion? Thanks in advance, Steve.
 

SydneyRoverP6B

Well-Known Member
Staff member
#3
Hello Steve,

It largely depends upon the climate in which you live. Using an 88 degree thermostat in a cool to cold climate is fine, for anything else then an 82 right down to a 74 can be used. Other factors that can influence how hot an engine will run include ignition timing, fuel mixture, compression ratio, radiator size along with cooling system condition and of course as to whether the car runs an automatic transmission with the inbuilt cooler within the radiator still in use.

Ron.
 

chrisyork

Active Member
#4
And, of course, for whatever temperature thermostat you choose, it is essential that there is a pilot hole in the annular ring surrounding the stat itself. Original stats had this as standard with a small "jiggle pin inserted in it. modern stats tend not to have them, in that case it is quite in order to drill your own, about 1/8" is about right, and it must be sited at about 2:00 as you look at the engine.

The purpose of it is to ensure that there is always a small flow past the stat so that the stat gets to see the true temperature in the coolant nice and promptly.

Chris
 

redrover

Active Member
#6
I'd heard 83-87 was the optimum but does it vary from engine to engine? For the sake of completeness of information in one forum thread, should the 4-cylinder also sit at that temperature?

Fitting the oil cooler, electric fan and expansion tank this weekend, so cooling should no longer be an issue (not that it ever got beyond about 83 anyway). So once it's sorted, I would also like to run with optimum temperature coolant. Greater efficiency and warmer feet!

Michael
 

rockdemon

Administrator
Staff member
#8
mine is on 88 - Harvey i think said 88 and only go for the summer stats if the 88 gave trouble with overheating...

Rich
 

SydneyRoverP6B

Well-Known Member
Staff member
#9
redrover wrote,...
Fitting the oil cooler, electric fan and expansion tank this weekend
Hi Michael,

Is that an engine oil cooler or additional transmission oil cooler that you are referring to?

Ron.
 

SydneyRoverP6B

Well-Known Member
Staff member
#10
The rated temperature of the thermostat is the minimum at which it just begins to open. So an 88 degree C stat for example will begin opening at this temperature. Typically the thermostat will be fully open around 10 degrees or so above the opening temperature, so say around 98 degrees C as in the case of this example.

The thermostats fitted by the factory for cars destined for the Australian market were 82 degrees C. When cars had air conditioning fitted, thermostats would often be changed for either the hard to obtain 78 degree model or the more readily available 74 degree C option.

Ron.
 

redrover

Active Member
#12
SydneyRoverP6B said:
redrover wrote,...
Fitting the oil cooler, electric fan and expansion tank this weekend
Hi Michael,
Is that an engine oil cooler or additional transmission oil cooler that you are referring to?
Ron.
Hi Ron,

It's a series 2 2000 TC engine oil cooler (the one that goes under the horn, not under the radiator). I've put off fitting it for now as I've not had a spare weekend when I've not needed the car. I also needed to sort out the adaptor for the pressure sender gauge. If all goes well, I'll be fitting it this weekend, with updates to follow.

Michael
 

SydneyRoverP6B

Well-Known Member
Staff member
#13
redrover wrote,...
Hi Ron,

It's a series 2 2000 TC engine oil cooler (the one that goes under the horn, not under the radiator). I've put off fitting it for now as I've not had a spare weekend when I've not needed the car. I also needed to sort out the adaptor for the pressure sender gauge. If all goes well, I'll be fitting it this weekend, with updates to follow.
Hi Michael,

Thanks for that.. :) hope the installation all goes well. I look forward to reading of your progress!

Ron.
 
#14
rockdemon said:
88 is spot on - you go lower if you suffer overheating.

Rich
The UK EFi 3.5/3.9 V8's are supposed to run an 88deg stat. As mine tends to go mad with the 88deg fitted I have an 82deg stat installed now. It now runs at a constant 82deg instead of 135deg :shock:

A cooling system service helped with the overheating issue on 88deg stat, but I now prefer the 82deg for peace of mind, as it is much more stable. They say the only downside to running the cooler stat is a tendancy to use more fuel, as in theory, the computor is telling the injectors to put slightly more fuel in - thus less economical.
 
#15
A higher coolant temperature also improves engine effiiency. It's a thermodynamic fundamental similar to the advantage gained by raising compression ratios. That's why motorcycles go to the trouble of using oil as the coolant instead of water. It's also why Land-Rover took the inadvisable risk of running the serpentine and later engines at much higher coolant temperatures.

For goodness sake don't take that as a hint to use higher temperatures in our engines. Even in new condition, the internal coolant passages inside the cylinder block and heads are insufficiently scientific to stand running things too close to the theoretical ideal. There's far too much chance of localised hot spots, and if you take the opertaing temperature too high they turn into localised boiling.

Chris
 

SydneyRoverP6B

Well-Known Member
Staff member
#16
chrisyork wrote,...
A higher coolant temperature also improves engine effiiency. It's a thermodynamic fundamental similar to the advantage gained by raising compression ratios. That's why motorcycles go to the trouble of using oil as the coolant instead of water. It's also why Land-Rover took the inadvisable risk of running the serpentine and later engines at much higher coolant temperatures.
Very true Chris. The 4.0 and 4.6 litre Rover V8 engines used in Range Rover up until 2004 ran with a thermostat that didn't open until 96 degrees C, so 106 degrees C before it was fully open. High operating temperatures reduce harmful exhaust emissions, so in order to run cleaner, they need to run hotter. The 4.2 and 4.4 litre Jaguar engines used in the Range Rover Sport that followed ran even hotter, with the thermostat not opening until 108 degrees C, and fully open at 118 degrees C... :shock: With such a high operating temperature and running such tight clearances, there was absolutely no room for error, so if for what ever reason the engine ran hotter than this, the goose would be literally cooked!

Ron.
 
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