pd 170 not your average overheating thread

[tallpaulselfrid]

Hi guys, here again to pick your collective brains.

So I had the usual cracked head issue on my '07 PD170 (BMR code)

Got a second hand, skimmed and pressure tested head and fitted it along with new timing belt and water pump, so all that is new.

While at it I deleted the EGR & Cooler with Darkside bits and gutted the DPF. Then mapped it with a Celtic tuning eMotion unit to map out the EGR & DPF software.

I drove to South Wales last week from here in Scotland and did 500 miles there without a hitch, including being stuck in a 6hr tailback on the M6 with all the stop start involved in that. When I was literally 20 miles from pulling up, the temp gauge went through the roof and the low coolant warning came on.

The system is over pressurizing now. If I crack the cap on the expansion bottle it all comes back. I have checked for blockages and air locks and have re-filled the system twice now, including flushing the heater matrix and checking for flow through the rad. When I filled it last I did it systematically going through every hose connection from bottom up trying to release air. The top hose feeds back to the expansion tank fine.

Is there some secret wee corner of the block where air is getting trapped? Or some trick way of bleeding the system I haven't worked out?

Any help or advice gratefully received. I'm at my whit's end here!

[martin1810]

Sounds like head or gasket gone again.

[Quatrelle]

Just wondering what effect skimming the head would have on all this, how much was taken off, and why it was skimmed in the first place - warped and still warped? - hence the head gasket worry.

[DMitch16]

The problem with the "porous" heads was to do with the alloy mix and casting. There's nothing to stop a second hand head from the same period from developing the same symptoms after fitting even though it was fine and held pressure before. The only way imo to remove the risk is to fit a new head which should not have the underlying defects of the original bad ones. Although second hand heads are skimmed to ensure they are level did the block get checked and / or skimmed as there is the possibility that the block may not be fully level itself despite it being iron and not softer aluminium. I have put 15K more on the car since the change and the new head they put on seems fine.

Perhaps the extensive deletions and remaps have caused the replacement to give up too? Was it guaranteed at all?

[DMitch16]

Just wondering what effect skimming the head would have on all this, how much was taken off, and why it was skimmed in the first place - warped and still warped? - hence the head gasket worry.

Sorry to correct you but they skim second hand heads to ensure that they are as level as possible before being sold or refitted to another car (some do, some don't). It doesn't have to be warped to have a skim though. Warping however is not mentioned in connection with the second hand head that was sourced in this case?

[Quatrelle]

Sorry to correct you but they skim second hand heads to ensure that they are as level as possible before being sold or refitted to another car (some do, some don't). It doesn't have to be warped to have a skim though. Warping however is not mentioned in connection with the second hand head that was sourced in this case?
No problem, never too old to learn.

[DMitch16]

No problem, never too old to learn.

So true, my B6 has taught me many new things mostly that the old classics are much better to work on and seemingly more reliable! I do miss my Mk1 Escort refreshingly simple!

[Crasher]

VW state that the cylinder head must not be re-surfaced as it is heat treated to prevent porosity which you remove when skimming.

[DMitch16]

This may be the problem with the 2nd hand head used then perhaps?

[tallpaulselfrid]

Ooer, I almost wish I hadn't read these replies. Although they're greatly appreciated.

i think porousity, cracks and warps can be ruled out though. The car holds pressure when warm and hot (very hot these days), so any of these problems should surely cause loss of pressure and coolant.

I've no smoke, it runs fine and I haven't lost another pre-turbo egt sensor. It used to eat these for breakfast with the old cracked heat as the exhaust gasses were super heated steam!

[Crasher]

Presumably when you rebuilt it you fitted a new water pump. It may be a failed thermostat but does the fans run really hard when it overheats?

[martin1810]

eek! Crasher are you really posting at 04.23 am or is the clock on here wrong.

[Crasher]

I am having trouble sleeping all of a sudden, really bad!