As much as i love this site, I thought I had finally fixed my problem so I didnt have to come on here everyday searching for answers..:doh:

Anyway, 2.5 DSE, auto.

Had problems with it overheating under load about a month ago.

Found the viscous coupling to be knackered, so decided to overhaul cooling system.

Replaced the thermostat, waterpump, header tank cap, viscous unit, and fan.

Before and after replacing all these parts the temp needle sits about a MM to the right of the 12 o'clock white line. (is this normal?)

Drove it today for 3 hours, stopping twice for about 15 minutes each time.

Did 60-70 steadily on the motorway on the way there, some gentle town driving at 30-40 and then 70 again for about 40 mins on the way home (temp needle never moved), as I came off the slip road and around the round-about the temp gauge started moving up towards the red, as soon as it touched the first red line I turned it off and coasted it into a layby.

Now this is where I am confused, on the first ever previous overheat I had steam pouring out of the header tank and breather tank, and had to top it up with cool water

This time although the gauge had gone into the red, there was no steam, and no bubbling, I sat for about 5 minutes let it cool, went back to normal temp, set off again, needle moved up again to the red within 20 seconds, as soon as It moved I pulled over, sat for another 5 mins until needle moving back to centre, slowly unscrewed the header cap, let the pressure out without letting any coolant out, the coolant level returned to normal.

Quick note, before letting the pressure out, the coolant level was higher than the cold level indicator (should it be lower than the mark, then rise when cold, or be higher when hot, then level lower when cool?)

Stuck my finger in to see how warm (yes not the brightest move, could have been burned) but as suspected, although it was warm as say a hot tap on, it wasnt boiling, just warm like a nice bath. So screwed cap back on, setoff, temp normal, drove remaining 35 minutes home with no trouble.

Again, no oil in water, no water in oil, no leaks what so ever, and no coolant loss at all, the level is still the same as when I topped it up this morning a few hours before I set off.

The A/C fans are currently not connected, and do not function at all, but I dont use the air con, so I didnt think this mattered.

Seems like a pressure problem, shouldnt the pressure slowly release when parked up over a night, as yesterday I took it out for an hour test run without problem after completing the parts change, parked it, checked the level this morning, and the system was still pressurised, is this normal? shouldnt it release pressure once turned off? Or am I wrong?

Finally, yes it sounds like a head gasket, or head problem, or cracked block, BUT, I dont have any coolant loss, If it was a crack or gasket, surely the coolant level would have dropped and coolant been lost?

And I have bled the system once the parts where fitted, topped up with cap off, revving at 2000 rpm for a few second, topping up until all air gone and complete. So Im sure its not an air lock either as it didnt happen until about 2-3 hours driving

Stumped, thought I'd fixed the problem, and really dont want to throw more money at it.

Any opinions welcome, dont just read it all and not comment

Could be something as simple as an airlock, but could also be a cracked head. Pressure should reduce as the water cools. Just a thought, but if the water wasn't hot, could be the guage or sensor playing up.

Rangie.lad said:

As much as i love this site, I thought I had finally fixed my problem so I didnt have to come on here everyday searching for answers..:doh:

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You should come on here to help and give assistance to others too...not just when you have a problem and you are looking for the answer....if we all did that, no one would get any answers only questions....

Don't be shy and share your experiences, you never know, it could help someone.....

Your symptoms sound exactly like what happened to my 2.5 DSE manual. It overheated in the highway because of bad viscous fan (the only part that I hadn't replaced yet). After putting a new fan in it overheated two other times, under little load. Eventually I found out that the tube that comes from the radiator into the expansion tank was blocked. Fixed this and it hasn't overheated yet even after 4 hours of mud play yesterday

Rangie.lad said:

As much as i love this site, I thought I had finally fixed my problem so I didnt have to come on here everyday searching for answers..:doh:

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What's wrong with us on here?!?!...............

Acctually...... Don't answer that

Saint.V8 said:

You should come on here to help and give assistance to others too...not just when you have a problem and you are looking for the answer....if we all did that, no one would get any answers only questions....

Don't be shy and share your experiences, you never know, it could help someone.....

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Haha, dont worry, I do browse everyday for new problems to try and solve, I just meant its was nice to not have to come back to solve my own problems

Thermostat? just mentioned it because no one else did

before you go doing head gaskett check the pipe going from rad to header tank make sure that is free. when your engine is running you should have a little water returning into the header tank this is visible so long as you havnt filled it to the top also sqeeze your pipes and you should see a squirt coming through . somebody might be able to second what im about to suggest and that is that in the top of your radiator there is a plastic divide which means that the water has to go down one side of your rad and up the other side if this piece of plastic is broken the water would travel across the top of your rad and not down through it to be cooled but i doubt that is your problem as your problem is not constant but if you want to check your rad put it on its side and put a marble in one pipe if it goes to the other side your rad is in trouble but as i said it does not sound like your problem as you dont seem to have overheated as you had no steam or boiling . best of luck . sean

I'm with Sean on that.

I've a seized viscous fan. Now I've looked at the overheating issues with the P38 for a long time. With the seized fan my car runs cooler than it should in most situations I only come up about 1mm above the lower white line whereas a year ago I would have been 1mm left of the 12oclock position. So that means my car is running cool which means it never get into the fully warm fuel map and is noisy as hell. All of which annoyed me, not least of which was the reduced power/increased fuel consumption.

Now in what might seem a suicidal move for a P38 DSE I decided one day to remove the fan completely for the hell of it

What happened next is a lesson for anyone with cooling problems on their DSE.
It didn't overheat.
I drove from Tralee to Mayo, a 250+ mile journey mixing motorway, regional roads and towns with some hills. Now it was late and I never once got stuck in traffic but in 10 degree ambient temp the car did not need the fan. When I got to Mayo I then had to go up a mountain on a windy forest track. Within a mile of going uphill at 35mph the needle started creeping up the dial. when it reached the top of the white line I pulled over, turned it off and put the fan back on. Drove on the rest of the way up the mountain no problem.

Moral of the story, if your car has a healthy pump, rad, thermostat and enough coolant it will not overheat in most normal conditions. If its overheating at motorway speeds then you've got a problem with one of the above, it wont be anything to do with a viscous fan.

But as Datatek said above they are very prone to airlocking. I was changed the thermostat a while back and had a job to get it to take the water again.

Incidentally, while changing the thermostat I decided to leave off the shroud to make taking the fan on and off easier. The car runs a little warmer with the same seized fan as before but not much and still too cold.

Recap:

You've driven for a fairly long distance at a good speed and the engine didn't overheat until you slowed down so the radiator managed to keep the engine cool at speed, but it possibly couldn't transfer the extra excess heat with a slower air flow (reduce speed).

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The engine cooling fan pulls air through the radiator to replicate the vehicles higher forward speed under slow/stopped speed conditions but if the radiator is boarderline unservicable/blocked. Could it be that its not capable of removing the excess heat from the system causing overheating after a high speed run at slower speeds.

You state you've overhauled the cooling system but haven't listed a new radiator, have you had the radiator checked for flow or replaced the radiator?

lots of good comments above but can I suggest one little one I don't think was mentioned.

when you refilled with water after sorting the fan, did you let it run without the water cap on to let all the air out?, this might be the only issue having changed the fan. let it run until the water expands and starts to overflow.

good luck.

spud still driving with that seized fan

Dopey mentioned the thermostat. I fitted a new 'quality aftermarket' thermostat as part of a refit of radiator, pump, belt and tensioner. I still had a problem so put the old OEM 'stat back in and it seemed to help. So, I ordered a new BMW 'stat and fitted that and it did make a difference. I am not against Britpart et al but I am not sure that their tolerances are as tight as the originals in some cases.

Rangie.lad said:

Seems like a pressure problem, shouldnt the pressure slowly release when parked up over a night, as yesterday I took it out for an hour test run without problem after completing the parts change, parked it, checked the level this morning, and the system was still pressurised, is this normal? shouldnt it release pressure once turned off? Or am I wrong?

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Missed this on first reading. It would be well worth your while changing the expansion tank cap. These have been known to cause odd overheating issues.

seanmull said:

spud still driving with that seized fan

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Yeah Sean, they're flippin expensive and I don't like them.

I'm also thinking of doing Datatek's trick of using the aircon fans instead of it. They worked really well like that on the RRC3.9 and it seems stupid that they don't act as emergency cooling on the DSE as standard. Like I said it ran without a problem with no fan until I went off road and you know how they like to get warm when shown a steep hill

I'll leave the shroud off, not needed in Ireland, and keep the fan and a 32 mm spanner in the back for off road work. It takes 30 seconds to put the viscous back on when the shrouds not in the way. That'll save the aircon fans of which I have a spare pair anyway from the 98 in Relihans.

SpudH said:

Yeah Sean, they're flippin expensive and I don't like them.

I'm also thinking of doing Datatek's trick of using the aircon fans instead of it. They worked really well like that on the RRC3.9 and it seems stupid that they don't act as emergency cooling on the DSE as standard. Like I said it ran without a problem with no fan until I went off road and you know how they like to get warm when shown a steep hill

I'll leave the shroud off, not needed in Ireland, and keep the fan and a 32 mm spanner in the back for off road work. It takes 30 seconds to put the viscous back on when the shrouds not in the way. That'll save the aircon fans of which I have a spare pair anyway from the 98 in Relihans.

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Done mine, works great. You can get the adjustable thermostat you need from Conrad Their part no is 615889 - 89 and is Manufacturer part no.: 100924

seanmull said:

before you go doing head gaskett check the pipe going from rad to header tank make sure that is free. when your engine is running you should have a little water returning into the header tank this is visible so long as you havnt filled it to the top also sqeeze your pipes and you should see a squirt coming through . somebody might be able to second what im about to suggest and that is that in the top of your radiator there is a plastic divide which means that the water has to go down one side of your rad and up the other side if this piece of plastic is broken the water would travel across the top of your rad and not down through it to be cooled but i doubt that is your problem as your problem is not constant but if you want to check your rad put it on its side and put a marble in one pipe if it goes to the other side your rad is in trouble but as i said it does not sound like your problem as you dont seem to have overheated as you had no steam or boiling . best of luck . sean

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I am sure I have seen instances mentioned where new radiators have been made without the baffle. Always best to check this before fitting a new rad or refilling an old one.