' 86 5000 csq avant oil pressure relief valve

Huw Powell audi at humanspeakers.com
Sun Jan 11 17:20:26 EST 2004

> I have a '86 5000 csq avant. The manifold cracked, so I tore 'er apart. In
> the process, I noticed that the turbo was leaking oil, so I replaced that,
> installed a K&N air filter, new gaskets, etc and bolted everything back
> together again. 
> The car drove and ran fine, for about 50 miles, then the radiator blew.

> Get new radiator, install radiator in
> true shade tree mechanic style, car starts right back up, but then I notice
> it's leaking oil like a mother.
> Had car towed back home, start to take off all the tin on the front around
> timing belt, etc, and it appears now that I have all the oil cleaned up that
> the leak was coming from the Oil pressure release valve, not the main seal
> or anything like that.

The "oil pressure relief valve" is not a one-shot device, or even a 
safety thing like the pressure relief things on biolers and hot water 
heaters.  It is basically a heavy spring pushing against a fairly simple 
piece of tube with a couple of holes in it, and when the output of the 
oil pump reaches the maximum "allowed," (5 bar? 7 bar?) it recycles some 
of the oil bac through the pump, only allowing that "maximum" to get to 
the engine.  So it is a constantly functioning mechanism.

It is mounted in a round, verticallly oriented cavity that opens to the 
bottom of the oil pump.  As pointed out previously, the "sealing" device 
is either the oil temperature gauge sender (and they tend to leak quite 
nicely) or just a big bolt.  I suspect the chances of this leaking are 
pretty slim, although, anything is possible.

More likely culprits in that area are the main crank seal, your turbo 
oil lines (especially since you just replaced the turbo and might have 
roughed them up - poor old rusty things that they probably are by 
now...), and up higher, the cam oil seal.  Although an oil pump/timing 
belt cover bolt or two can leave a gusher oil leak if not installed 
correctly, it doesn't sound like you messed with them.

Since you have the engine in pieces now, so none of these theories can 
really be tested, you might as well just reassemble it with new (or very 
good used) parts every where you can.  It's a very old engine, and while 
its main guts are probably still good for many more miles, the stuff 
bolted on around it is probably pretty sketchy by now.

That's why you are getting this cascading failure of major systems 
effect, I think.  They're all old and waiting to die, and major work 
under the hood either raises the strain on old parts, or actually 
stresses them out physically by working aorund them.  (was that a 
sentence?)  It's time to get pro-active and take things off and replace 
with new *before* they break.

Others please feel free to chime in and correct any incomplete or 
erroneous explanations...

Huw Powell



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