p38 2.5 diesel..driving me crazy,overheat issue

Bought a p38 last month,bought it with a split rad at top....I'm quite ocd about bmw and cooling systems..so I put in New rad,New water pump,thermostat,viscous fan ,New drive belts,oil change ,New air filter,and replaced all hoses with new....before this it had a slight overheating problem,...I assumed after a good bled it would be all good...but no ,I can drive 30-60mins stays at just before 12 on gauge ,when I come to a stop in traffic ..the temp rises to red and red light comes on ...stop for 1min and temp goes back down again ...this happened every drive....I can idle on start up for a hour ,take it for a drive around ,then park up and it starts overheating again ...changed coolant to g13 as well...anyone she'd any light on this ...many thanks Johnny...I've bled it to death ,also have book warning on the hevac system which comes and goes...other than that it drives spot on ...awaiting a eBay sniff test this week....but I'm seriously puzzled as I'm not losing coolant and oil is clean...

This does sound like a strange one... The split rad that you bought it with... What caused that? pressure in the system? Have you checked the new rad is working its not unknown for new parts to fail too. The rad should get hot all the way from top to bottom with no cold spots...

If it's not overpressuring with the over heat maybe you should be looking at the temp sender. First one on head near injection pump. Check that new rad has a baffle in it.

Cheers I'll go down now and check ....clean temp sensor and check that ...ooh man gotta take rad off again loool....pretty sure rad is good tho ...but I'll recheck to cross it off lost...have no idea why the rad split was4years old by receipts I got ...previous owner is a liar so can't be trusted on what he told me ...

johnnysensi said:

Cheers I'll go down now and check ....clean temp sensor and check that ...ooh man gotta take rad off again loool....pretty sure rad is good tho ...but I'll recheck to cross it off lost...have no idea why the rad split was4years old by receipts I got ...previous owner is a liar so can't be trusted on what he told me ...

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If you look at the rad from the front. Hot coolant comes in from the right, flows down to bottom and up left hand side of rad back to engine. There should be a baffle half way across header tank to ensure this flow. If it's not there coolant just flows across the header tank back to the engine and does not go through the radiator. Check that rad gets hot at the bottom if it doesn't odds on no baffle. That would give you your problems.

Thank you wammers

Is your viscose fan working propely you should hear it in traffic.

If the viscous fan is ****part, it could be that too. Baffle missing in the RAD is a good bet as Wammers said, do the marble test.

Looks like electrical problem, maybe poor earth connection somewhere.
Maybe it is overheating only when brake pedal pressed?
Check that it is really overheating. Does putting hevac on maximum heating reduce temperature?
With temp guage on maximum and red light on, there should be a big pressure in cooling system and coolant escaping from expansion tank cap.

Took it for a drive ...maybe 40mins in all with 2stops..rad was warm all over not overly hot ...I jetwashed the air con rad has it was clogged up with dirt n oil gunge...Top hose was hot ...hose to thermo was warm ...when it does start to overheat the heater trick don't work ...it didn't overheat tonight ...when it does over heat u can hear a hiss from expansion tank like there some serious boiling going ..viscous wasn't a britpart...current thermostat is a britpart 4quid job....I have a spare motorrad thermostat I can use ...I've also taken the air con fans out to test them tonight as the motors look very rusty on the outside ,and also I've never seen them spin ,in fact when I took em out they had mouse poo all over em ,which would not be there if they run ,as the spinning would have dislodged it ....when do they run ???

I could press my hand on the rad all over after 20mins drive ....it's 1° at Mo would have thought it would have been hotter myself

johnnysensi said:

Took it for a drive ...maybe 40mins in all with 2stops..rad was warm all over not overly hot ...I jetwashed the air con rad has it was clogged up with dirt n oil gunge...Top hose was hot ...hose to thermo was warm ...when it does start to overheat the heater trick don't work ...it didn't overheat tonight ...when it does over heat u can hear a hiss from expansion tank like there some serious boiling going ..viscous wasn't a britpart...current thermostat is a britpart 4quid job....I have a spare motorrad thermostat I can use ...I've also taken the air con fans out to test them tonight as the motors look very rusty on the outside ,and also I've never seen them spin ,in fact when I took em out they had mouse poo all over em ,which would not be there if they run ,as the spinning would have dislodged it ....when do they run ???

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Aircon fans only run when aircon gas temperature is too high detected by pressure. On later cars they also operate in an engine overheat condition.
Sounds like it's either the stat sticking or the RAD baffle is missing.

johnnysensi said:

Took it for a drive ...maybe 40mins in all with 2stops..rad was warm all over not overly hot ...I jetwashed the air con rad has it was clogged up with dirt n oil gunge...Top hose was hot ...hose to thermo was warm ...when it does start to overheat the heater trick don't work ...it didn't overheat tonight ...when it does over heat u can hear a hiss from expansion tank like there some serious boiling going ..viscous wasn't a britpart...current thermostat is a britpart 4quid job....I have a spare motorrad thermostat I can use ...I've also taken the air con fans out to test them tonight as the motors look very rusty on the outside ,and also I've never seen them spin ,in fact when I took em out they had mouse poo all over em ,which would not be there if they run ,as the spinning would have dislodged it ....when do they run ???

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Fit a genuine thermostat with the vent uppermost. Cheap thermostats are foolish economy. You failed to mention the over pressure in your earlier post.

Sorry wammers,I just assumed it was a airlock making the hiss when it overheats....going down to.change my heater pipes now and refit air con fans ...and drill a hole in the circoli thermostat I bought ...and then off for a lovely drive thru Kent to Sussex to see how it goes ..thank you both for your help and advice so far ,it's great to have extra brains working it out ...

Just done all what I was advised....been on idle for 20mins...temp is at 11 so far,which cooler than its idled before ...now raining so I'm sitting in cab watching my temp gauge....should both rad pipes be hot ??thermostat pipe is stone cold

johnnysensi said:

Just done all what I was advised....been on idle for 20mins...temp is at 11 so far,which cooler than its idled before ...now raining so I'm sitting in cab watching my temp gauge....should both rad pipes be hot ??thermostat pipe is stone cold

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Thermostat pipe will get hotter when stat opens. Mine will idle for ages without going to mid point you need to take it for a run.

Thermostat pipe got warmer ..after sitting there for some time...cross me fingers,getting the mrs and going out now ...cheers fella for your quick answers...and advice ...

Went for good 1hour n half drive,hit some traffic ,hit some traffic lights,no temp raise ....got home ,Sat on idle for good 20mins...just about to get out and thought I'd stay for 5more mins...and temp gauge started to climb just before red....all hoses were hot as they should be ...but fan looks like it wasn't doing it's job,I'm going to take it.back to island 4x4 and hopefully change it ....I thought it would have more kick as the temp was just before red ....with engine off I can turn it with only slight resistance,goes round maybe 7inches or so when u grab blade and free turn it....��unhappy bunny cost me 118quid ...I'm going to put some self tappers in my old fan ,and go for same drive tomorrow before I take it back ,just to be sure ...I heard 2screws in front face of fan should lock it in fast position...so running cool all the time ....

johnnysensi said:

Went for good 1hour n half drive,hit some traffic ,hit some traffic lights,no temp raise ....got home ,Sat on idle for good 20mins...just about to get out and thought I'd stay for 5more mins...and temp gauge started to climb just before red....all hoses were hot as they should be ...but fan looks like it wasn't doing it's job,I'm going to take it.back to island 4x4 and hopefully change it ....I thought it would have more kick as the temp was just before red ....with engine off I can turn it with only slight resistance,goes round maybe 7inches or so when u grab blade and free turn it....��unhappy bunny cost me 118quid ...I'm going to put some self tappers in my old fan ,and go for same drive tomorrow before I take it back ,just to be sure ...I heard 2screws in front face of fan should lock it in fast position...so running cool all the time ....

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You could do the aircon fans mod and use them for cooling.
Careful locking the fan solid, they can break up
A duff cap on the expansion tank can cause problems, make sure it is fully screwed down, they go tight before they are fully down.

Do not lock the fan solid! It's big and heavy fan and it will explode(or go through radiator) if you give it some revs!

Make sure that all radiators are clean from outside - air flow restriction will boil coolant very quick.