Re: [DMCForum] Continuing misadventures of a Volvo/B280F PRV

[Martin Gutkowski <martin@xxxxxxxxxxxxxx>]

Hi Carter

You haven't stated the general condition of your cooling system. I've 
known of a car that would do exactly as you describe - work fine at low 
speerd but overheat on the motorway, and that was down to a blocked 
radiator.

However, I would say that if you talk to a mechanic who works on a lot 
of cars (and who has done head gaskets - many shy away from them!) 
he/she'll undoubtedly have a story of a car which showed up as fine in 
all the tests thrown at it but still wouldn't either run right or 
overheated etc. Changing the head gasket(s) is usually the last thing to 
think of in moments like that but once done, everything works fine.

I did a pair of gaskets on a DeLorean last month. The only clue was that 
the coolant kept disappearing when there were no leaks, and it would 
overheat really sporadically. It'd be fine for a hundred miles, then 
overheat on a 6 mile trip. In the DeLorean it's vital to keep a healthy 
level of coolant because once the level drops below the bottle, it drops 
in the pump (most cars will drop in the rad first which is less 
critical). As soon as the pump loses water - no circulation and overheat.

The filler cap on that car was full of chicken soup but the oil was 
fine. Buf on cars that sit for a few months and then get driven do 
accumulate a bit of soup there anyway thanks to condensation. The only 
real evidence once inside was in the heads and on the timing cover. 
Liner seals almost never fail "on their own" - they usually fail due to 
the liners being lifted when the heads are off, then not being cleaned 
up and replaced. When they fail, you get loads of coolant strait into 
the sump, and you're not getting that.

Hope this helps

Martin

cartermartin wrote:

> Sorry in advance for the long post.
>
> Ok so I think I have gotten to the bottom of my Volvo 760GLE/B280F-
> PRV problems or at least nearly to the bottom of it.
>
> I have essentially rebuilt my  cooling system. Along the way I did
> every possible test I could think of for a blown head gasket or
> cracked head. These include:
>
> - Compression test. I got 180-185# on all 6 cyl. The numbers might be
> suspect but felt the fact they are so close together was more
> important.
> - Cooling system pressure test. After all the cooling system work was
> done. I pressure tested it at 22# (factory spec for this model) for
> 15-20 minutes. I had very little, if any, leakage.
> - Tested the cooling system pressure under normal running conditions.
> Pressure was built gradually up to 15-20# or so.
> - A block leak test. The gizmo that detects exhaust gasses in the
> coolant by drawing air thru the coolant.
>
> Anyway after all of this I still have coolant loss and evidence of
> high pressure in the system. In this case coolant blown out of the
> expansion bottle.
>
> The only other clue was the chocolate milkshake on the filler cap.
> When I changed the oil I found no evidence of coolant.  And after 2
> negative 'block leak' tests (i.e. no combustion gasses) I finally got
> a positive after a highway run (where btw it urped out a pint or so
> of antifreeze).
>
> It appears that under light load, idling or driving around the
> neighborhood, there is not a problem. This manifests itself at
> freeway speed when I hear a buzzing sound from time to time that I
> believe is either the pressure being vented past the radiator cap or
> perhaps even gasses blowing past the head gasket. The latter may be a
> long shot but the sound is coming from the opposite side of the
> engine from the coolant bottle.
>
> At this point my suspicion is either:
>
> - small head gasket leak
> - Cracked head
> - or maybe a seal for the cylinder liner?
>
> I'm still a neophyte on these engines and since it's an old Volvo
> sedan (as opposed to something more exotic) I should probably walk
> away. But I feel I want to get to the bottom of all of this. It is
> also difficult because it's running SOOOOO good.
>
> Any thoughts, ideas, or suggestions would be appreciated? Any PRV
> mechanics in the Atlanta area who can do a head/head gasket, please
> step forward.
>
> Oh and for what it's worth I did get the Y-Pipe o-rings sealed up.
>
> Carter

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