P38 heater o-rings: draining tips?

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P38 Monkey

P38 Monkey

Well-Known Member
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Just changing the leaky heater o-rings on my GEMS P38, as you do.
Haven’t done this before, but am using Stufer’s excellent guide.
When it comes to draining the heater rad, Stufer suggests a plastic sheet in the driver's footwell, and allowing the coolant to run out over the sill. But is the alternative method of disconnecting the hoses in the engine compartment and blowing air in, less messy? I only have a 12v tyre pump, which I guess may not produce enough air to do the job.
Should I be clamping any hoses to stop excessive coolant loss?
Any tips greatly appreciated…
 
P38 Monkey said:
Just changing the leaky heater o-rings on my GEMS P38, as you do.
Haven’t done this before, but am using Stufer’s excellent guide.
When it comes to draining the heater rad, Stufer suggests a plastic sheet in the driver's footwell, and allowing the coolant to run out over the sill. But is the alternative method of disconnecting the hoses in the engine compartment and blowing air in, less messy? I only have a 12v tyre pump, which I guess may not produce enough air to do the job.
Should I be clamping any hoses to stop excessive coolant loss?
Any tips greatly appreciated…
Click to expand...
I used compressed air to blow dry the heater matrix, I'm not sure your 12 volt tyre pump will produce the volume or air needed.
I just blocked the ends of the coolant hoses with cut down wine corks but if you raise the ends as high as possible, not much coolant will leak out.
 
Last edited:
That’s all good info - and of course practical, as to be expected on this forum. I plan to clamp the hoses, then blow dry the matrix. Prefer to get the coolant out via the engine compartment rather than risk spilling lots into the footwell. Just waiting for the bits to be delivered… Thanks again.
 
On my diesel, I couldn't get the hoses off without ruining them. I drained the coolent from the rad only and didn't get much spillage from the matrix at all. Bin bag, split open is very thin and was easy to stuff up the gap under the matrix. The pipes to the matrix are at the top so just doing the seals leaves the coolent in the matrix, that doesn't need draining. Don't know what method you are following but I guess it's the hole saw in the side, cut the ducting method?
I struggled to cut the ducting plus its close to the alloy pipes going to the matrix so you may damage them if you are not careful.
A mate did his last year and heated up an old kitchen knife and just melted through the ducting in no time but I never witnessed that.
 
Flossie said:
On my diesel, I couldn't get the hoses off without ruining them. I drained the coolent from the rad only and didn't get much spillage from the matrix at all. Bin bag, split open is very thin and was easy to stuff up the gap under the matrix. The pipes to the matrix are at the top so just doing the seals leaves the coolent in the matrix, that doesn't need draining. Don't know what method you are following but I guess it's the hole saw in the side, cut the ducting method?
I struggled to cut the ducting plus its close to the alloy pipes going to the matrix so you may damage them if you are not careful.
A mate did his last year and heated up an old kitchen knife and just melted through the ducting in no time but I never witnessed that.
Click to expand...
A Stanley knife cut the ducting easily for me.
 
pwood999 said:
Take the dash out & do it properly. That way you can also sort any sticky flaps & failing servos.
Click to expand...
I sort of agree with that. I was new to p38s when I had to do mine and taking the dash out seemed daunting but when you look at what you have to remove to do the quick method..its not much more to remove the dash completely.
Cutting the duct however, for future hvac motor problems anyway, is much quicker. I can get to 'O' ring or hvac motor problems in around 30mins on the rhs . No good for sticky flaps though agreed.
Were you the chap trying to split a heater box to release some flaps a while back? If so, how'd you get on?
 
Flossie said:
I sort of agree with that. I was new to p38s when I had to do mine and taking the dash out seemed daunting but when you look at what you have to remove to do the quick method..its not much more to remove the dash completely.
Cutting the duct however, for future hvac motor problems anyway, is much quicker. I can get to 'O' ring or hvac motor problems in around 30mins on the rhs . No good for sticky flaps though agreed.
Were you the chap trying to split a heater box to release some flaps a while back? If so, how'd you get on?
Click to expand...
Yes it was me, but other stuff got in the way. It's sitting in the back of the garage waiting for time !! Meanwhile the one in the Blue P38 has the distribution motor hanging loose & the flaps in a position that shares the warm air between the screen & footwells. Book is on, but both blend flaps still work !!
 
All was going well, I discovered that the down pipe had already been cut, and then sealed with sticky-backed foam. I freed off the joint and rotated the upper part, but I cannot remove the lower part. Can’t get it past the lower joint - see photo. Any tips?
 

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The top bit doesn't need to be turned. Just the long lower part needs removing. I forget the little details but almost certainly you've left one or both of the lower screws in and it won't come out from below because of the shape of it. Out through the top, clocks out? Metal bracket that the clocks fix to been removed?
 
Thinking about it some more, I did remove the tee piece that you've rotated and the ducting that goes to the rh side window demister. That might have been to enable the lower ducting to be pulled up and out OR it might have been because it was all floppy near the vent and I was getting a buzzy noise behind the clocks at certain revs, thinking that might have been the sound...I refitted it better. The horizontal bit to the vent has a screw at the top which you can't get to I cut the 'ear' off the duct leaving the screw in place.
 
All sorted, a bit of leverage and some wiggling. Never thought of getting it out upwards, I just looked at where the previous owner had broken the various mountings, loosened those screws and took it out downwards. Instruments were already out, and left hand bracket too. As per above comments, there are two mounting points midway along the pipe, but neither of those screws was fitted… Why are all previous owners ham-fisted muppets?
 
pwood999 said:
Take the dash out & do it properly. That way you can also sort any sticky flaps & failing servos.
Click to expand...

I'd second that, I did mine over two days in February of this year, o-rings and blend motors replaced, heater box foam seals renewed, flaps checked and lubricated, plus replacement instrument & switch bulbs, and wiring in a GROM Bluetooth unit. It was *so* much easier with the dash out, I followed the excellent guide from PaulP38.com. I used loads of cheap ziplock bags and a sharpie to number fixings etc. by each stage of the instructions and laid out the removed trim parts with bagged fixings on top of each.

Managed it all single-handed - even getting the dash in and out - but it took about 40 minutes of to-and-fro to get the dash/bolts aligned to the vehicle on first reinstalling the dash before reassembly could commence in earnest.

It was also the only way I ever got oil to the right place to cure the infuriating brake pedal squeak!
 
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