Thread: Disco 1 V8 3.9 autobox strange hot running

Hi everyone,

I have a warm running 3.9 V8 disco 1 autobox that I would appreciate some ideas about.

I live in New Caledonia, so quite warm tropical climate.
Engine has been completely rebuilt 5000 km ago by a mate when I bought over this car.
It now has 192000 km on the clock.

I have fitted from the beginning an aftermarket VDO gauge for water temp and oil pressure monitoring.

Since I started driving this car, after the initial warming and stat opening cycle (that I can see on the aftermarket gauge), temperature has always sat on the 93°C mark, whatever town, road, hill, offroad, trailer driving.
Yet, what was quite annoying is that apart from a few minutes from cold start, the viscous fan was nearly always on, even on open road, up to 3000 rpm !!! I was under the impression of driving an airplane :-)

So I though the viscous was "too stiff" and decided to replace it by a new one, along with an 82°C stat to make it run a little bit cooler to be on the safe side in our climate.

Yet, now I am banging head on the wall : "if it's not broken, don't fix it !!!"

First, I shouldn't have done both at the same time.

Second, from then on, it is running much warmer !!!
I can not say overheat, because looking at the water temp gauge all the time, I have always stopped before boiling (never passed 105°C, never heard boiling coolant nor coolant passed the expansion tank cap or steam visible)... but if I had drove it only with dashboard temp gauge... who knows

Yet, I am stuck.

Here is what I have done since :
-> with new 82°C stat and PR2 ALLMAKES viscous, I could barely heard the viscous, only in slow traffic and under 2000 rpm, yet it runs hotter than 93°F (about 98/100°C)
-> replaced the new PR2 ALLMAKES viscous by a GENUINE LR one : same behaviour ! (so 2 new viscous same behaviour)
-> replaced the 82°C stat by a gutted stat in which I have removed the center bullet to fake a constant open stat : same behaviour !!!
-> new expansion tank cap

And here is the last complete test done, looking at temps with VDO gauge, plus rovergauge on computer, telling the same :
-> town driving, temp would vary from 93 to 97 °C
-> open road driving at about 90/100 kmh, 97/98°C (around 2000 rpm)
-> hitting a hill when road driving, would climb up to 105°C !!! (not passed 2000 rpm - can not hear the viscous)
-> but as soon as coming down the hill, would fall back down to about 92°C, and then on flat ground, will come back to the 97°C again
-> from then, as soon as I stop to open the hood, I hear the viscous engaged (and by the way, the electric aux fans in front of grill running also), and if i give it a fast 1000/1500 rpm idle, it roars and temp fall down to 93/94°C (and aux fans switch off as they should)

-> When climbing a steep hill, first gear, low range, all diffs locked, at about 1000/1500 rpm, temp steady 97°C
-> then on flat ground low range, up to 2000 rpm, viscous roaring, temp fall back to 93, even 92...

Aux fans working as they should.
Viscous locking when steady or at really low speeds (low range) or when town driving mainly when moving off, then free wheels
Cooling system does not seem to over pressurize, and no exhaust smell when poping off the expansion tank cap
Thermostat not sticking !
Took off 8 plugs, no signs of coolant or steam wash
No signs of coolant on oil filler cap nor on dipstick (oil level constant)

What do you guys think about all that ?

I am left with 2 main things :
-> clogged radiator, as I have no past service history, it might have the car's age (15 years)... he might be well clogged, and that might have been hidden up to now by the first viscous being locked nearly all the time and over forcing air through ?
-> unfamous head gasket leak or cracked block... but why this becomes only visible following stat + viscous change !?!

What is strange, when loading the engine in low range, so with viscous more engaged, it would not overheat as much as in high range, at the same rpm... so I hope it would only be the radiator just being not efficient enough, so when not "over forcing" air through it, it would not cool down coolant enough when loading engine, leading to running hotter ?

Thanks in advance for your opinions and knowledge.

Cheers.

Erik.

Originally Posted by Gary S11

Well I never new the disco had a engine oil cooler. Just googled it . Well I'll have to have a better look at mine as I've never even noticed any pipes . Only the g/box pipes
I guess if the new radiator seems to be the culprit, assuming no pipes are kinked or crushed then fitting a after market one if there's room and bypass the rad might be a way to go. Sorry not much help

Not a good idea to bypass the oil cooler in the radiator (unless damaged) as when idling in traffic or slow low range off-road work the stand alone aftermarket oil cooler will not be getting cooled as much as it would be if it was still routed through the radiator, unless you put a large electric fan to operate at idle speeds, Regards Frank.