P38 air lock

This site contains affiliate links for which LandyZone may be compensated if you make a purchase.
mercanlandy

mercanlandy

Active Member
Posts
155
P38 2.5 (BMW straight 6)
Have had a few overheating issues since having to replace a split hose at rear of engine. Refilled system with new coolant and water. All seems good but temp gauge sits a full mark higher on temp guage, more near center of normal. Before problem with split hose it would always sit just at top of blue cold mark. After runs of 20 miles it starts boiling over. I was suspecting head gasket damage but I have just had mobile mechanic round to do tests for head gasket failing, all tests showed no issues with head gasket. No bubbles coming into test rig and chemicals did not change colour which would have indicated exhaust gases in header tank. The mehanic says problem is either an air lock or water pump not pumping water around or a blocked radiator. I did put a tin of head gasket repair fluid into the water system following the hose splitting issue just in case any head gasket damage may of occured. I now think this may have blocked the radiator causing the engine to over pressure and boil up. Or an air lock. I fitted a new thermostat last week but problem is still the same. What is the proceedure for purging air properly out of water system. Last try before I replace water pump and radiator.

All help, getting desperate now
 
First thing did the new stat have a bleed hole in the outer part, if so was it fitted so that it was at the top.
 
The Radiators do not like leak blockers. They can be a difficult to bleed, make sure there is a trickle of water from the radiator breather pipe to the expansion tank. With the car idling, rapidly squeezing and releasing the main hoses helps expel any air.
It's easier if you jack the front of the car up a bit.
Easier than bleeding the system on my MR2:)
 
It is supposed to sit straight up in centre of gauge. Putting radweld or similar in before the engine is up to full temp could be fatal. Bleed pipe from o/s top of rad MUST be clear of coolant. Coolant is circulated from block into heater and then back to head via C shaped hose at n/s rear of engine until the stat opens. You could have blocked the heater, back flush it to be sure it's clear. Stat MUST have bleed hole in it set to top. I always fill rad and block separately by removing n/s top hose. Is it actually boiling over, expelling coolant from header tank? It may well be an air lock sometimes they are bitches to shift. By the way you cannot repair a leaking head gasket were the combustion gas is leaking into a water gallery with additive it's not possible.
 
wammers said:
It is supposed to sit straight up in centre of gauge. Putting radweld or similar in before the engine is up to full temp could be fatal. Bleed pipe from o/s top of rad MUST be clear of coolant. Coolant is circulated from block into heater and then back to head via C shaped hose at n/s rear of engine until the stat opens. You could have blocked the heater, back flush it to be sure it's clear. Stat MUST have bleed hole in it set to top. I always fill rad and block separately by removing n/s top hose. Is it actually boiling over, expelling coolant from header tank? It may well be an air lock sometimes they are bitches to shift. By the way you cannot repair a leaking head gasket were the combustion gas is leaking into a water gallery with additive it's not possible.
Click to expand...
 
HI, thank you for reply. Yes coolent is boiling up into the header tank. I did drill 2, 3mm holes in the new stat I fitted as I could not see any in it. I put new stat in same orientatuon as original with hole at top. It probably is an airlock but I have made matters worse adding the gasket repair fluid, in fact I have probably blocked the radiator or heater rad. It's a really good P38 so I am going to percivere and fix it. I am going to replace the water pump and radiator, back flush the heater radiator the recharge the coolent carefully getting all air out. I did a lot of reading yesterday on the forum regarding overheating issues and also replacement radiators. I read with interest that some after market radiators do not have a baffle in the top so water does not flow down through the radiator so fails to cool normally. Do you know of any after market radiators which are reasonably priced and do actually have this baffle in? I also read that some or most replacemeant water pumps only have 8 blades on the impeller and not 11 like the original. Do you think this would be much of an issue if any.

Regards

S.C
 
mercanlandy said:
HI, thank you for reply. Yes coolent is boiling up into the header tank. I did drill 2, 3mm holes in the new stat I fitted as I could not see any in it. I put new stat in same orientatuon as original with hole at top. It probably is an airlock but I have made matters worse adding the gasket repair fluid, in fact I have probably blocked the radiator or heater rad. It's a really good P38 so I am going to percivere and fix it. I am going to replace the water pump and radiator, back flush the heater radiator the recharge the coolent carefully getting all air out. I did a lot of reading yesterday on the forum regarding overheating issues and also replacement radiators. I read with interest that some after market radiators do not have a baffle in the top so water does not flow down through the radiator so fails to cool normally. Do you know of any after market radiators which are reasonably priced and do
actually have this baffle in? I also read that some or most replacemeant water pumps only have 8 blades on the impeller and not 11 like the original. Do you think this would be much of an issue if any.

Regards

S.C
Click to expand...
Island 4 X 4 supply Nissens radiators, I have one on my P38 and it's been fine.
I assume you checked the thermostat opens correctly BEFORE you fitted it? There are a lot of duff ones on the market. Need to stick it in a pan of water on the stove and heat it up and watch it open.
As for the water pump, do not get a plastic impeller rubbish BMW one, get one with a metal impeller.
 
Datatek said:
Island 4 X 4 supply Nissens radiators, I have one on my P38 and it's been fine.
I assume you checked the thermostat opens correctly BEFORE you fitted it? There are a lot of duff ones on the market. Need to stick it in a pan of water on the stove and heat it up and watch it open.
As for the water pump, do not get a plastic impeller rubbish BMW one, get one with a metal impeller.
Click to expand...
fgh
 
Hi. thank you for the reply. No I did not do the boiling water in a pan to check the new stat. I do believe it opens though as after running the engine all the hoses come up to temp and the temp gauge sits just below center. I have drained and bled the water system again and The small hose frim the top of the rad to the header tanl is clear, with the engine running I can see the water flowing from the rad into the header tank so its defo not blocked so any air should have purged from the system. I filled the water system from various points and the radiator to make sure its full. The heater works great and engine temp stays in center of gauge with heater on or off. I have been out for a run again today for about an hour running the motor at various speeds and it all looked great so I thought it must have been an air lock which I had now cleared. However after my last high speed run when I was sitting at traffic lights it boiled up again. Is it possible that the header tank cap could be faulty and not allowing pressure to realease?
 
mercanlandy said:
Hi. thank you for the reply. No I did not do the boiling water in a pan to check the new stat. I do believe it opens though as after running the engine all the hoses come up to temp and the temp gauge sits just below center. I have drained and bled the water system again and The small hose frim the top of the rad to the header tanl is clear, with the engine running I can see the water flowing from the rad into the header tank so its defo not blocked so any air should have purged from the system. I filled the water system from various points and the radiator to make sure its full. The heater works great and engine temp stays in center of gauge with heater on or off. I have been out for a run again today for about an hour running the motor at various speeds and it all looked great so I thought it must have been an air lock which I had now cleared. However after my last high speed run when I was sitting at traffic lights it boiled up again. Is it possible that the header tank cap could be faulty and not allowing pressure to realease?
Click to expand...
Could be a faulty header tank cap not holding pressure, it needs the pressure to stop it boiling.
 
mercanlandy said:
Hi. thank you for the reply. No I did not do the boiling water in a pan to check the new stat. I do believe it opens though as after running the engine all the hoses come up to temp and the temp gauge sits just below center. I have drained and bled the water system again and The small hose frim the top of the rad to the header tanl is clear, with the engine running I can see the water flowing from the rad into the header tank so its defo not blocked so any air should have purged from the system. I filled the water system from various points and the radiator to make sure its full. The heater works great and engine temp stays in center of gauge with heater on or off. I have been out for a run again today for about an hour running the motor at various speeds and it all looked great so I thought it must have been an air lock which I had now cleared. However after my last high speed run when I was sitting at traffic lights it boiled up again. Is it possible that the header tank cap could be faulty and not allowing pressure to realease?
Click to expand...
I presume you have checked the viscous coupling on the fan.
 
What the op describes as his latest symptoms happened to me on one of my Rangies.
I just could not get it to stop doing it (dumping water after a run) and despite pressure tests etc. etc. which failed to reveal a leak of any kind it finally stopped after a single treatment of the much maligned "Bar's-Leaks" (oh no, I said the BL word).After that, it never happened again. No idea what the root cause was.
 
You must log in or register to reply here.

Similar threads

farriermatt
Water problems 300tdi in a 1985 110
Replies
10
Views
711
farriermatt
farriermatt
enjoi
P38A Going through radiators- not overheating
2 3 4
Replies
60
Views
4K
enjoi
enjoi
P
Sport Coolant not circulating
Replies
11
Views
749
pllaw
P
M
Pressure in coolant
Replies
2
Views
517
biketeacherdave
biketeacherdave
MikeFl4
P38A Possible coolant in oil
Replies
9
Views
893
Datatek
Datatek
Back
Top