TWO failed thermostats in 2 months ??

About a month before my holiday mid Aug, I replaced the thermostat and water pump on my 2002 4.4. Better safe than sorry I thought as I had a "Activation Map Cooling" error showing which means the electric element had blown in the stat and I wasn't sure on the history of the pump so whilst in there did both. Any how, sure enough 3 days into my hols we had a boil up. Liquid levels checked out and after a bit of head scratching a new viscous coupling we ended up diagnosing a stuck shut stat. Coolant was reading 115deg but the bottom hose and bottom of rad where stone cold. Local garage pulled the insides of the stat out to keep me mobile and on return home I put a new stat in and monitored the temp to make sure all was good. Temperature stayed pretty static at 106 deg + - so assumed all was good. A couple of weeks later and I get the call from my lady saying its boiled up again - exactly the same again, temp right up cold bottom of rad.
Now have I been damn unlucky or is there something Im missing here ??

Forgot to mention rad is only six months old as well, so sure this isn't blocked.

could be saints prob aswell similar thing has happened to him recently maybe a faulty batch of rads/stats ?

wil2813 said:

could be saints prob aswell similar thing has happened to him recently maybe a faulty batch of rads/stats ?

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Hmmm intriguing....

My stat is prob 2 years old now I think...or close to it....but the rad is a few weeks old....hmmmm will be intrigued to follow this thread.

I am considering using a lower temp stat as I mentioned previously to bring the temp down, just to give more wiggle room.....

Saint.V8 said:

Hmmm intriguing....


I am considering using a lower temp stat as I mentioned previously to bring the temp down, just to give more wiggle room.....

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I'm currently running " Sans stat" but have read a few threads you mentioned earlier. I'm waiting for my BMW e65 4.0d stat to arrive - allegedly identical but 88deg and no electrical heater Will report when fitted.

Sitting here pondering this mystery, I'm starting to suspect that the waterpump may be weak. If I let her idle the temp creeps up to nearly 100, and this is without a stat in. Both fan checks out but I'm not getting any dribble from the little hole just inside the header tank cap- not unles I rev it hard and then I get a spurt this is making me think the impellor may be undersize and only pumping when given welly. Any volunteers to check if they have a stream from the little hole in the expansion tank on idle. ???

rewmer said:

Sitting here pondering this mystery, I'm starting to suspect that the waterpump may be weak. If I let her idle the temp creeps up to nearly 100, and this is without a stat in. Both fan checks out but I'm not getting any dribble from the little hole just inside the header tank cap- not unles I rev it hard and then I get a spurt this is making me think the impellor may be undersize and only pumping when given welly. Any volunteers to check if they have a stream from the little hole in the expansion tank on idle. ???

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On the L322, I have rarely seen it...open the bleed screw and give it some revs and I can water the garden with the spray....

NOW....

On my E38 BMW with the sme engine (M62) albeit the 3.5 litre version, there is good flow from the little hole in the expansion tank!

Have checked the little expansion hose and that is clear, just no discernible flow at idle from the hole on the L322!!!

rewmer said:

Any volunteers to check if they have a stream from the little hole in the expansion tank on idle. ???

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will report shortly off to work first

rewmer said:

Any volunteers to check if they have a stream from the little hole in the expansion tank on idle. ???

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Just checked mine. Yep there is a stream from the hole at idle.😀

GullH said:

Just checked mine. Yep there is a stream from the hole at idle.😀

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Hmm....might have to check mine when I get home.....is this at idle engine warm or from cold??

Saint.V8 said:

Hmm....might have to check mine when I get home.....is this at idle engine warm or from cold??

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That's from idle warm, Saint.

GullH said:

That's from idle warm, Saint.

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Ta, will check!! (Worried now )

This is getting interesting. I'm sure there should be some flow from the weep hole. I am almost certain there was before I changed the pump, maybe not a jet but at least a dribble.

rewmer said:

This is getting interesting. I'm sure there should be some flow from the weep hole. I am almost certain there was before I changed the pump, maybe not a jet but at least a dribble.

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Not getting a 'jet' at warm idle.....but definitely a steady stream on the weep hole. Will make a little video and post it to the 'tube' for you to compare...

GullH said:

Not getting a 'jet' at warm idle.....but definitely a steady stream on the weep hole. Will make a little video and post it to the 'tube' for you to compare...

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Lovely, thanks v much. The more comparisons I can get the better. I'm starting to be convinced all pumps aren't built equal.

rewmer said:

Lovely, thanks v much. The more comparisons I can get the better. I'm starting to be convinced all pumps aren't built equal.

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Hi Rewmer,

Video posted at

L322 4.4v8 Expansion Tank Bleed Test - YouTube

Hope it helps....😊

GullH said:

Not getting a 'jet' at warm idle.....but definitely a steady stream on the weep hole. Will make a little video and post it to the 'tube' for you to compare...

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Will do same when I get back!

One thing I may need to point out is this test needs to be done cold. These engines run at 105 deg so the cap needs to be off before it gets up to temperature otherwise we are going to have scolding water sloshing about - not good fo people nor engines ! So please people, be careful and let those engines cool right down before removing the cap.

Thanks for the vid Gull, Obviously you have good pressure there but Im looking for confirmation that the pump creates enough flow from cold to create a squirt or dribble from the hole inside the expansion cap.

rewmer said:

One thing I may need to point out is this test needs to be done cold. These engines run at 105 deg so the cap needs to be off before it gets up to temperature otherwise we are going to have scolding water sloshing about - not good fo people nor engines ! So please people, be careful and let those engines cool right down before removing the cap.

Thanks for the vid Gull, Obviously you have good pressure there but Im looking for confirmation that the pump creates enough flow from cold to create a squirt or dribble from the hole inside the expansion cap.

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Ahh...ok...so how do I do this? Start it from cold and check the bleed screw whilst at idle?

Let it cool right down, give it several hours and then take the header tank cap right off. You should see a small hole inside the neck. This is where I'm looking for a stream of coolant / dribble. It's only a small hole and hard to see so best wait till morning light.

rewmer said:

Let it cool right down, give it several hours and then take the header tank cap right off. You should see a small hole inside the neck. This is where I'm looking for a stream of coolant / dribble. It's only a small hole and hard to see so best wait till morning light.

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will do mine in the morning then as the girlfriend has been out thus afternoon with ours.