P38A [P38] Common coolant leak locations

blue_cheese · Aug 10, 2025

marjon said:
Thought,
You do the pressure test and all is good. Have you changed the cap? It’s the only thing not in the equation when you pressure test it.

I understand that hot/cold can make leaks elsewhere but a new cap is not a lot of beer tokens .

J

I've not noticed any leaks or puddles around the cap, so I hadn't thought about replacing it yet.

It does sometimes screw on funny, so maybe it's worth a punt for a few quid

pwood999 · Aug 10, 2025

If it's only a small amount missing, chances are it's evaporated by the time you look for it !!

blue_cheese · Aug 11, 2025

I do check under the bonnet when I get home, and haven't spotted anything obvious yet. The coolant also tends to leave a distinct stain on my driveway for a few days.

It's going in for suspension work later this week, so I'll ask the guys to have a quick look while the car is up on the ramps

marjon · Aug 11, 2025

I know it can be difficult to locate a small leak, but does the puddle it drops give a clue to an area.

J

blue_cheese · Aug 11, 2025

Sorry should have clarified,

When I had a bigger coolant leak in the past, a stain was being left on the driveway.
Now there's no stain being left, so I don't have any clues.

pwood999 · Aug 11, 2025

Did you do the pressure test wiht the engine hot ? If not, get it properly warmed up for a few miles, and then do the pressure check.

blue_cheese · Aug 11, 2025

Will give that a go this afternoon

Datatek · Aug 11, 2025

blue_cheese said:
Will give that a go this afternoon

Careful how you take the cap off the expansion tank because the coolant could boil over.

pwood999 · Aug 11, 2025

+1 ^^^^^^ Release the pressure slowly using a thick towel or rag on the cap.

brianp38dse · Aug 12, 2025

A common leak item is the the throttle body heater which can be bypassed from the system if needed.

blue_cheese · Aug 16, 2025

Always something else with these cars

Went to the garage yesterday for wheel alignment, I told them there was a slight exhaust smell in the cabin and asked them to look in to it.

They said the gaskets they used when fitting new cats for it's MOT hadn't been fitted properly, and they would replace them free of charge.

Got the car back today, and the engine seems a lot louder and growlier, also seems to pop a bit when the revs drop quickly.

Is this normal for these engines? Sounds like I've left with a hole somewhere!

blue_cheese · Aug 16, 2025

Right, been at it today with the pressure testing.

Warmed the engine up, then fitted the pressure tester. Went to about 14 psi.

Waited about half an hour, and the pressure had dropped to about 11 psi:

And after an hour, it was just shy of 8 psi:

So I'm definitely losing pressure to something, and after looking around, I did spot this little puddle under the throttle body:

So I guess I know what I'm changing next, fingers crossed this will be the last of this problem.

Datatek · Aug 16, 2025

blue_cheese said:
Right, been at it today with the pressure testing.

Warmed the engine up, then fitted the pressure tester. Went to about 14 psi.
View attachment 347805

Waited about half an hour, and the pressure had dropped to about 11 psi:
View attachment 347806

And after an hour, it was just shy of 8 psi:
View attachment 347808

So I'm definitely losing pressure to something, and after looking around, I did spot this little puddle under the throttle body:
View attachment 347807

So I guess I know what I'm changing next, fingers crossed this will be the last of this problem.

The pressure will drop as the coolant temperature drops but it sounds like you have found the leak.

brianp38dse · Aug 16, 2025

The throttle body heater can be bypassed its not really needed in our climate, that way it will never cause a leak again.

blue_cheese · Aug 16, 2025

brianp38dse said:
The throttle body heater can be bypassed its not really needed in our climate, that way it will never cause a leak again.

Would that just be a case of removing the two hoses and connecting them together? Or just get one length of house and connect them both on their sources?

brianp38dse · Aug 16, 2025

Just connect them together and see how it goes if no more leaks then you have sorted it and can leave like that or alter pipe work to reduce possible leak points.

blue_cheese · Aug 16, 2025

Thanks, I'll have a look in the morning for some suitable pipes/hoses to join them together

blue_cheese · Aug 17, 2025

Quick and simple solution, disconnected input + output of the throttle body heater and connected them together with a hose connector.
And extra clamps just to be sure.

Hope the connector is rated for at least 120⁰C.

Any issues with this setup before I take it for a test drive?

Grrrrrr · Aug 17, 2025

Looks OK.

P38A [P38] Common coolant leak locations

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