Bizarre M52 cooling system problem

[Aubs]

This is pretty much driving me nuts now, so hopefully some of you will be able to come up with some suggestions:

Last week the car was fine, after nothing at all untoward happening the car started oveheating.

A quick testing session revealed that when the car was up to and above normal running temperature, the rad and top hose were cold, and there was no movement of the coolant in the header tank.

I thought "Thermostat", but then checked the heaters, they are also cold at running temp.

thought the water pump may be dead (plastic blades broken up?), but pulled that out and it is a perfect condition one with metal blades.

The only other thing I can think of is that theres a blockage somewhere, going to try and get hold of a hosepipe so I can see what happens when I run some water through the block.

Weird eh? Any ideas?

[daimlerman]

Only three places that can stop water circulating;
Thermostat
Pump
Radiator

[Aubs]

True, but the radiator being blocked wouldn't cause the heaters to blow cold would it?

What i'm thinking atm is some kind of obstruction in the block.

[Aubs]

Ok, just flowed some water through the radiator top hose, and it flowed freely out of the bottom.

[DanThe]

The water pump impeller hasnt come loose from the pulley shaft has it?

[Aubs]

Dan, it feels pretty secure to me, what's the best way of checking?

[Aubs]

Yup, that was a stupid question, just gave the bearings a good wiggle and it seems perfectly solid.

[Jhonno]

Heater matrix piped correctly?

[Aubs]

Heater matrix piped correctly?

I'm guessing so, can't see how it would have worked before otherwise. If it was, would it interfere with the entire system?

[Jhonno]

Yes it would interfer I believe..

[Daf318is]

Have the heater pipes become trapped behind the block somehow when you changed the sump?

Did you remove these pipes when you changed the sump and put them back on the wrong way? It's very tight down there - it's possible something has been disturbed when the engine mounts were off.

[Aubs]

Good idea, I can just about get my hand around the back to trace the path of the lower one [which you cant see much of], and it seems ok. the top one isn't obviously caught by anything either.

I didnt remove them, but just to confirm they are in the right places, the bottom hose goes to a connection on the back of the block, and the top one goes to a port on the side.

[Daf318is]

Yes that hose is correct. It worked for me for 2 years anyway

If the hosepipe test doesn't show anything up the only thing I can suggest is to fill it slowly and make sure it's bled properly.

[Aubs]

An update: after completely draining the system and reassembling, it will only take 1 litre of water. I switch the engine on, and the level remains the same. Pulled the bottom hose off the rad, and water comes out, so id hazard a guess that the problem is between this thin bottom hose and the block. Goning to have to take the inlet manifold off to get a closer look.

Any more ideas?

[turk]

thermostat on the right way round? and free? try blasting air thru the ports after taking pipes off maybe?

[DanThe]

As you fill the rad the coolant will flow through the bottom hose into the engine and around the system, starting the engine before its full will only make the problem worse as the water pump will just pump air into the system. Park the car facing uphill before filling, did you take the bleed screw out of the rad?

[Aubs]

I had the car facing up my driveway, with a slight incline. The bleed screw was out of the rad. Are you suggesting I need to fill the header tank over half way to get enough coolant into the block?

@ Turk - Stat has been out and tested, also it only fits one way round.

[Aubs]

You were absolutely right Dan, this evening I put the front up on stands. It took around 3.5 - 4 litres. Ran it for a while with header cap and bleed valve off, after the second attempt I managed to get the heaters to blow hot when revving the engine, leaving it to idle caused them to cool off again. I repeated this for a while until they were lukewarm continually.

Getting dark now so ill repeat the process tomorrow, perhaps getting the front end a bit higher. Thanks for all your help so far guys, ill let you know how it goes.

[Brianmoooore]

Filling a modern engine with coolant isn't like filling an old Morris Minor! There's plenty of trapped air and potential for airlocks, and the consequences of these can be expensive.
The coolant bottle has to be kept filled right to the top, bleed screws opened and pipes massaged.
If the heater circuit isn't playing ball, take off the top hose at the bulkhead, and push it back on when coolant flows from both halves.

[Aubs]

All sorted now thanks chaps, turns out a good bleeding was all it needed. Can't figure out where the air lock came from in the 1st place, but I'm sure time will tell if it happens again

[Daf318is]

Good good! Well done

[aceraf]

Just been reading this thread as i've had a similar problem as mentioned by the OP, but mine has got worse. Water is leaking out somewhere near the back of the block. Is there a a pipe that could split at the back of the block (near the bulk-head)?

Problem started when i took the car (M52 B28 E39) for mot where the MOT'er kept revving the car to get it hot enough to pass the emissions test. Shortly after it developed an air-lock. I bled the system successfully, but it kept happening again (i can tell when something isn't right as my car is LPG converted, and when the problem occurs it won't switch to LPG as it thinks the car is cold).

It's now leaking water (constant slow drip at the back of the block).

Any idea's?

[town325i]

Just been reading this thread as i've had a similar problem as mentioned by the OP, but mine has got worse. Water is leaking out somewhere near the back of the block. Is there a a pipe that could split at the back of the block (near the bulk-head)?

Problem started when i took the car (M52 B28 E39) for mot where the MOT'er kept revving the car to get it hot enough to pass the emissions test. Shortly after it developed an air-lock. I bled the system successfully, but it kept happening again (i can tell when something isn't right as my car is LPG converted, and when the problem occurs it won't switch to LPG as it thinks the car is cold).

It's now leaking water (constant slow drip at the back of the block).

Any idea's?

At the rear of the cylinder head there is a alloy pipe that is similar to the one on the rear a m20 head this could be leaking also there is another thing that bungs the cooling system on the back of the head but im not sure what its called

[DanThe]

Could be due to where the vaporiser is plumbed into the cooling system

[aceraf]

Update:

found the pipe at fault, it was the one connected to the connection from the engine block, however it was a bit more complicated.

The pipe coming off the block led to a T-pipe that went off to the LPG system, so it's the piece added by the LPG installed that had failed.

This wasn't therefore a stock part, so i've had to make up a replacement from a straight piece of pipe my brother bought for me from a local motor factor. The piece that was in there was a curved piece, where as I could only buy straight pipes, so the pipe now has a slight kink to it.

Is this going to be a big problem? The piece i removed also had a kink in it, however was slightly curved, although i don't know if the reason for that was the heat from the water over time re-shaping it slightly or whether it was meant to be like that.

[Brianmoooore]

LPG tee is usually fitted by chopping 1/2" out of the middle of the original BMW pipe.