L322 Viscous Fan Coupling issues....Very Odd....

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Saint.V8

Dyed-in-the-wool 100% RR Junkie
Full Member
Wonder if someone could proffer a suggestion or insight...

Long story short....

Last Summer on Hols in the IoW, she kept over heating, so I replaced the stat and viscous coupling....

Better but not brill.....traced it down to the gearbox oil cooler stat causing an airlock (remember the thread?? - Over pressure etc)

So removed stat from housing and have been running for the best part of a year without the stat with no issues.....engine temps remain in the late 60's to mid 70's most of the time, pushing hard she rises to the early 80's but thats it....

Recently (last few weeks) the VC has been locking up even though the engine is running 30-40 deg lower than design... at idle it is fine and slips like it should, but above 1200-1500rpm it roars like a banshee, if you keep the revs up above 3.5k the fan will start to slip again properly as it should, but once the revs drop back to normal, in a couple of seconds the fan locks up again....

So at the weekend I replaced the VC with a new one, and this one does the same thing.

Checked the engine temp via hidden menu, diagnostics and also using a temperature probe....all show the engine is running cool around the late 60's, you can even hold the top hose like it is a hot cup of tea, so the engine is definitely not hot enough to trigger the fan to lock up.....and this is a new coupling too....so something is a miss....

Did try running without the fan, but when sitting in traffic or at lights the temps do rise without this additional cooling of the fan drawing air over the rad at tick over.

Confused I have to say....the engine is running cooler, it is a new coupling and when the previous coupling was fitted there was no issue until about a month ago or so.....

Any ideas?
 
Wonder if someone could proffer a suggestion or insight...

Long story short....

Last Summer on Hols in the IoW, she kept over heating, so I replaced the stat and viscous coupling....

Better but not brill.....traced it down to the gearbox oil cooler stat causing an airlock (remember the thread?? - Over pressure etc)

So removed stat from housing and have been running for the best part of a year without the stat with no issues.....engine temps remain in the late 60's to mid 70's most of the time, pushing hard she rises to the early 80's but thats it....

Recently (last few weeks) the VC has been locking up even though the engine is running 30-40 deg lower than design... at idle it is fine and slips like it should, but above 1200-1500rpm it roars like a banshee, if you keep the revs up above 3.5k the fan will start to slip again properly as it should, but once the revs drop back to normal, in a couple of seconds the fan locks up again....

So at the weekend I replaced the VC with a new one, and this one does the same thing.

Checked the engine temp via hidden menu, diagnostics and also using a temperature probe....all show the engine is running cool around the late 60's, you can even hold the top hose like it is a hot cup of tea, so the engine is definitely not hot enough to trigger the fan to lock up.....and this is a new coupling too....so something is a miss....

Did try running without the fan, but when sitting in traffic or at lights the temps do rise without this additional cooling of the fan drawing air over the rad at tick over.

Confused I have to say....the engine is running cooler, it is a new coupling and when the previous coupling was fitted there was no issue until about a month ago or so.....

Any ideas?

Maybe the VC is going down Ant. Not locking up and spinning free is not the only fail mode, sometimes they lock solid and will not release. Have seen a few like that.
 
Maybe the VC is going down Ant. Not locking up and spinning free is not the only fail mode, sometimes they lock solid and will not release. Have seen a few like that.
Cheers Tony,

This is a new VC fitted a couple of days ago....it is showing the same signs as the year old one fitted previously that for the first 10/11 months has worked flawlessly...then started locking up, so replaced...new one doing the same thing!
 
Cheers Tony,

This is a new VC fitted a couple of days ago....it is showing the same signs as the year old one fitted previously that for the first 10/11 months has worked flawlessly...then started locking up, so replaced...new one doing the same thing!

That's unlucky to get two duffers are they genuine of pattern?
 
That's unlucky to get two duffers are they genuine of pattern?
Genuine....Behr/Hella

The one I changed last year worked fine....until recently...now the new one is doing the same.....wondering if there is something else in the game causing this...but the engine is running cool so unlikely to be the engine temps causing lock up!
 
Genuine....Behr/Hella

The one I changed last year worked fine....until recently...now the new one is doing the same.....wondering if there is something else in the game causing this...but the engine is running cool so unlikely to be the engine temps causing lock up!

Don't know to be honest, maybe the engine temp could be a factor not warming the fluid enough to make it flow or making the open valve close to quickly because of lack of residual heat. Normally the fluid is in the centre of the hub and when heat is present the hub opens a valve to allow the fluid to centrifuge out and lock the fan. Maybe this is happening because heat is marginal. When the hub is hot the centrifugal force diminishes with lower RPM and fluid should flow back loosening the lock. Maybe because heat is marginal the valve is closing to early not allowing fluid return at lower RPM.
 
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