4.4v8 cooling questions

well i seem to still be getting high temperatures if stood in traffic for periods of time it peaked at 110 degrees the other day, this is after fitting a 80 degree thermostat kit, i've flushed the system through and put new coolant in but it's made no difference. so i have 2 possible causes.

1st being i have a alternative gearbox oil cooler fitted that is mounted onto the radiator i do notice at motorway speed and after climbing a hill temp does rise, it usually reaches upto 97 degrees at 70mph motorway use, and can peak at about 102 after climbing a hill so some of these temp differences could be down to the gearbox oil pumping extra heat to the cooler and transfering to the radiator.

2nd is the viscous fan and this is where i need help as there seems to be 2 ways people say these work.
some say they are temperature controlled and cut in around 95 - 100 degrees.

others say it's speed controlled (this includes on the bmw forums) so at idle speed it should be fully engaged, i guess this is with engine temp hot or cold.

anyway regardless of which above as soon as i start to get moving engine temp drops quite quickly, and i can feel hot air being pulled through the viscous fan, but i did the rolled up newspaper test this morning with engine temp at 95 degrees and ticking over i can stop the fan and get same resistance as if trying to turn the fan with the engine off. i certainly don't hear a roar from the fan running.

currently i've done 137000 miles so not sure how long these viscous units should last.

sounds like the viscous fan has gone they work on temp not speed.

brianp38dse said:

sounds like the viscous fan has gone they work on temp not speed.

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As above, temperature operated, common failure item on LR products.

Now this is where the confusion is, the m62 viscous unit I'm pretty sure is rpm controlled not temp controlled, it has a flat plate on the front not a coiled bi-metallic strip, on the bmw forums they are all saying it should be fully locked on at low revs, then releases as engine speed increases

RRkev said:

Now this is where the confusion is, the m62 viscous unit I'm pretty sure is rpm controlled not temp controlled, it has a flat plate on the front not a coiled bi-metallic strip, on the bmw forums they are all saying it should be fully locked on at low revs, then releases as engine speed increases

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The flat plate is just a different manufacturers version of the bi-metallic coil, it appears on some P38's too. All viscous fans are temperature controlled and will be locked at idle when hot, being a viscous, slip will increase with revs due to load induced slip, bit like a torque convertor.
If you can stop it at idle, it's fecked.

The Viscous fan operates with increases in temperature.....

Now here is the operation as I see it.

The unit is filled with a fluid that at low speeds drags the fan around at Xrpm during idle...as the engine speed increases, the fluid starts to slip (hence why they are referred to as a viscous fan clutch) but as the engine rpm increases the fan rpm remains around Xrpm....so whilst it doesn't actually slow down as engine speed increases, it is slower than the engine.

As the temp increases, the bimetal strip expands and starts to lock the clutch up to prevent slip and the fan rpm starts to increase to follow engine rpm hence it gets faster.

Saint.V8 said:

The Viscous fan operates with increases in temperature.....

Now here is the operation as I see it.

The unit is filled with a fluid that at low speeds drags the fan around at Xrpm during idle...as the engine speed increases, the fluid starts to slip (hence why they are referred to as a viscous fan clutch) but as the engine rpm increases the fan rpm remains around Xrpm....so whilst it doesn't actually slow down as engine speed increases, it is slower than the engine.

As the temp increases, the bimetal strip expands and starts to lock the clutch up to prevent slip and the fan rpm starts to increase to follow engine rpm hence it gets faster.

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About what I said, however it should be emphasised that at idle with the RAD up to full temperature, the viscous should be in effect locked causing the fan to run at engine speed. It should not be possible to stop the fan with a rolled up newspaper.
The fan speed is self limiting, it should never as far as I know run at full engine RPM above about 1500/2000 rpm instead maintaining a more or less constant speed.
If the viscous seizes, the fans have been known to shed blades

Datatek said:

About what I said, however it should be emphasised that at idle with the RAD up to full temperature, the viscous should be in effect locked causing the fan to run at engine speed. It should not be possible to stop the fan with a rolled up newspaper.
The fan speed is self limiting, it should never as far as I know run at full engine RPM above about 1500/2000 rpm instead maintaining a more or less constant speed.
If the viscous seizes, the fans have been known to shed blades

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Spot on Keith, yes, should have made it clear that the fan speed does increase but is also not at full engine rpm when locked!

Had a fan shed blades my first Classic, that made me jump!

cool i'll get one on order cheers guys