P38 oveheating

Datatek · Sep 26, 2023

Wayne890 said:
So back on this again. I intended to rig the air con fans infront if the radiator to be on all the time to see if this helped with over heating. Turns out the passenger side fan doesn’t work even when connected directly to the battery so I have got the other fan to come on with the ignition. Does anyone have any experience or knowledge with these fans? What they should do when they should come on etc?

I use the fans for cooling instead of the viscous fan and have a mod to do this.
Normally they only operate when called by the aircon, they can come on at half speed or full speed, details in RAVE.
If one fan is faulty, the half speed function will not work as in order to get half speed, they are connected in series, for full speed they are connected in parallel.
Not really a good idea to try and mask the overheating fault.

Wayne890 · Sep 26, 2023

Can’t find any reason for it to be overheating now. I have tried everything. It’s fine driving around at 30 all day also happy to idol for hours. Even sat in stand still traffic and no problems. It only over heats now after a long drive at speed and it has to stop and have the heating off to over heat now.

Datatek · Sep 26, 2023

Wayne890 said:
Can’t find any reason for it to be overheating now. I have tried everything. It’s fine driving around at 30 all day also happy to idol for hours. Even sat in stand still traffic and no problems. It only over heats now after a long drive at speed and it has to stop and have the heating off to over heat now.

Lack of airflow through the RAD or condenser due to crap in the fins; duff RAD due to failed baffle or sediment in the bottom; duff viscous fan, duff or incorrectly installed thermostat; expansion tank cap not sealing; faulty water pump; faulty hose(s) restricting water flow; airlock in engine; lastly a cracked head.
Remover the thermostat and see if you still have a problem if you run with out it fitted.

Mark Piercy · Sep 26, 2023

You need to fix the overheat problem really and not the symptoms

Wayne890 · Sep 26, 2023

Easier said than done. It would be alright if I could find what’s causing it.

kermit_rr · Sep 26, 2023

Datatek said:
Lack of airflow through the RAD or condenser due to crap in the fins; duff RAD due to failed baffle or sediment in the bottom; duff viscous fan, duff or incorrectly installed thermostat; expansion tank cap not sealing; faulty water pump; faulty hose(s) restricting water flow; airlock in engine; lastly a cracked head.
Remover the thermostat and see if you still have a problem if you run with out it fitted.

Does the diesel have the same thermostat as the petrol? I know the rad is different

Datatek · Sep 26, 2023

kermit_rr said:
Does the diesel have the same thermostat as the petrol? I know the rad is different

No idea about the petrol. The diesel stat must have a hole at 12 0lock.

kermit_rr · Sep 26, 2023

Datatek said:
No idea about the petrol. The diesel stat must have a hole at 12 0lock.

Not the same then

Mark Piercy · Sep 27, 2023

What year is it?

Wayne890 · Sep 27, 2023

Grrrrrr · Sep 27, 2023

kermit_rr said:
Does the diesel have the same thermostat as the petrol? I know the rad is different

No, setup is different.

Early diesels the aircon fans don't come on at all. I cannot recall which of the stats on later ones triggers the fans but I seem to recall it is a higher temperature than you'd like.

Personally I like redundancy so I keep meaning to mod mine to make them come on but there are always too many other jobs to finish first.

Datatek · Sep 27, 2023

Grrrrrr said:
No, setup is different.

Early diesels the aircon fans don't come on at all. I cannot recall which of the stats on later ones triggers the fans but I seem to recall it is a higher temperature than you'd like.

Personally I like redundancy so I keep meaning to mod mine to make them come on but there are always too many other jobs to finish first.

The overheat sensor on the later diesels is the one in the head at the fire wall end. It tends to operate when the overheat is beyond recovery.
Using the electric fans for cooling is more reliable than the viscous fan, quieter and gives a quicker warm up in winter.

Wayne890 · Oct 6, 2023

Just incase any one is interested as these posts never seem to have a resolution. I took it to a different mechanic and within seconds he found that the pipe connecting the expansion bottle to the heater matrix had a tiny pin hole in it and was letting air in took him less than 10 minutes to find the hole and replace the pipe.

Rubberknees · Oct 6, 2023

Wayne890 said:
Just incase any one is interested as these posts never seem to have a resolution. I took it to a different mechanic and within seconds he found that the pipe connecting the expansion bottle to the heater matrix had a tiny pin hole in it and was letting air in took him less than 10 minutes to find the hole and replace the pipe.

Good outcome. Thanks for letting us know

Grrrrrr · Oct 7, 2023

Wayne890 said:
Just incase any one is interested as these posts never seem to have a resolution. I took it to a different mechanic and within seconds he found that the pipe connecting the expansion bottle to the heater matrix had a tiny pin hole in it and was letting air in took him less than 10 minutes to find the hole and replace the pipe.

Presumably he saw where the antifreeze was coming out? Hard to imagine air going into a pressurised system except as it cools.

Wayne890 · Oct 7, 2023

No no anti freeze leaking just a worn out pipe that had been rubbing

Grrrrrr · Oct 7, 2023

Wayne890 said:
No no anti freeze leaking just a worn out pipe that had been rubbing

Ah, where that nut is on the P-clip? I saw that when I got the car and wrapped some boke inner tube around it with some cable-ties just in case something like that might happen.

Mark Piercy · Oct 7, 2023

Grrrrrr said:
Ah, where that nut is on the P-clip? I saw that when I got the car and wrapped some boke inner tube around it with some cable-ties just in case something like that might happen.

I did exactly the same on mine and two other p38's. As it passes over the metal frame work above the airbag frame.

stemac33 · Oct 7, 2023

I put a p clip on mine and secured it with the bolt

Montyjohn · Oct 7, 2023

Wayne890 said:
Just incase any one is interested as these posts never seem to have a resolution. I took it to a different mechanic and within seconds he found that the pipe connecting the expansion bottle to the heater matrix had a tiny pin hole in it and was letting air in took him less than 10 minutes to find the hole and replace the pipe.

So I guess when it got hot at high speed it was loosing pressure through the pin hole.
Then when it cooled down it was drawing air in through the pin hole resulting in an airlock.

These pinholes are easy to find if you pump the system up to 15psi. You can hear the smallest hole hissing.

P38 oveheating

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