What is "high" mileage for a '91 S4 ? i can buy one with 240K kilometers ( 150K miles ) . Is this end of life or half way ?

 

Neither...

Its longevity will depend on its service schedule and detail. There will probably be deferred maintenance to catch up. Do it all!

 

i'm most concerned about the engine … other items we "can" fix.
Let's assume he had his oil /filter on time during his life.... what is 150K miles for the engine ?

 

You will also have to assume that he did the coolant changes on time as well. So assuming a 928 engine is properly maintained it's entire life, I have read that some folks have gotten to 500,000 miles and are still going.

Also what do you mean by "end of life"? Having to replace the block? Replace the heads? Or is having to replace engine internals your threshold? IMO end of life would be having to get a new block. Everything else is "feasibly" repairable/replaceable.

 

There have been 928s with literally 500k+ miles.

Greg Brown (GregBBRD) of Precision Motorwerks (as familiar with 928 engines as anyone) will probably back me up when I say that the biggest threat to the lifespan of the engine is old, acidic engine coolant. The gaskets go first, then the coolant eats at the tops of the bores. Naturally, the cylinder heads are at risk too.

I hold the opinion that anyone who wishes to expect indefinite performance for the years ahead from a 928 engine should make plans to replace the head gaskets, assuming there is no verifiable history that the work had been done recently.

 

yes gentleman , i'm concerned about the "engine" . I can buy it at almost the price of a good engine … but if i need another one the "goal " is away…..
it's a auto what i don't want …. but i have a manual '90 GT , ex race car , not worth rebuild. ( no engine, interior , dashboard etc... ) but i have all the needed parts for a swap to manual !
Nice winter project....

 

There are numerous examples well over 200k. There are a couple that are higher.

Properly cared for, the block & internals (rings & bearings) will last a long, long time.

I wouldn't call 150k miles 'super high'. Certainly a long way from 'done for'.

 

didn't buy the "cheap" S4... had it all what i do not like : exterior green , interior white and a lot of aluminium corrosion due it's life near the coast ….. so nogo. And auto, but goal was a manual swap , as i have all the parts from a '90 GT.

But more : i see for the first time a 32V... and used to wrench on 16 V's … no, i got afraid of that complex monster in there …. i stay for sure with 16V's. Even wondered why Porsche made that so complex, for 10HP more.... emissions ? My S 4.7 l 16V has 310 HP , that S4 32V 5L has 320 HP. What's the point ?

Swap is justified as decent auto here go's 15K , a decent manual 25K.

 

Sounds like you been around 928 so you know the pitfalls...
Mine is at 250k miles and my automatic transmission just gave up FWIIW. Engine is still pulling strong when I feel like going 5 mpg! But the tranny replacement still hurts just the same, I suppose...

 

Well looked after 928's have gone far beyond 250k miles on original engines-transmission with just routine maintenance. As mentioned above the key is to drive them and don't let them sit for too long as the coolant will become an issue along with other things like pests eating wiring etc.

 

indeed IcemanG17 , that car was in a garage for 10 years unused … and had problems with electric wiring …. and fuel . Owner already drilled out the return line because it was blocked !
Coolant is of course the same as 10 years ago….

 

Now at 320,000, used twice a week, all the important bits work, normally go to West Palm Beach once a year 620 miles, interior is sun damaged, mostly stock.

 

the problem isn't the mileage, as others have stated it is the coolant attacking the head gaskets there are some really low mileage cars out there that will have head gasket failures.

 

Checking crankshaft endplay is important. Seems to me that there have been quite a few thrust bearing failures reported here over time.

 

Mostly that issue falls with the 4 speed autos. My own 89 almost did as its flex plate was bowed at least 4mm. Probably the absolute limit before crank meets block.