around 300psi compression, time to kiss goodby?
 

my darling SDL, is loosing power,

300 psi compression test,+/- all six cylinders.,

looks like, time to stop the money in,

drives 80 miles/hour, freeway,

climbs by shifting gears,

no blow-by,

375,000 miles,

(tons of spar part, and oil,)

any input from this wonderful forum,

thanks any which way

Probably time to have the head overhauled or upgrade to a newer casting. When the valve guides wear out, the valves no longer seat properly and you get compression leakage. If you don't have blow-by problems, the bottom end is still pretty solid meaning the compression loss isn't coming past the rings and into the crankcase.

If you haven't done it already, pull the intake manifold and clean all the crap out of it. My SDL was so choked up with muck that it was breathing through intake runners about the size of my pinky finger.

Thanks a lot for your quick input,

just called Metric engine, in North Hollywood,

$310 for new valve guide , compression test,

++++ gasket, new bolts+++
looks positive,

some changed valve guides without taking the head out,

You can change the valve guide SEALS without removing the head. The valve guides themselves are part of a head overhaul and require the head to be removed. Once they're installed, clearance has to be checked to the valve stems and the seats re-ground.

As for the reduced power, you could be having issues with the turbo failing to spool properly or fuel supply issues. It's worth checking how much boost you're making, you should be making 12-14PSI when the engine is under heavy load such as accelerating or pulling up a hill. When's the last time you changed the fuel filters? Replaced the rubber fuel hoses? Air in the fuel supply will certainly reduce power.

Thanks for your help,

I have booster gage on my dash, turbo shows 12 psi, under load,

new FF, hoses,

have the parts to change seals in the inj. fuel pump,

did diesel purge,

timing chain slack is zero,

love the car,

ok seals is one thing, guides are other thing,

thanks

Yes, the seals are part of a valve guide job and can also be done separately. My SDL had iron valve guides originally, at 173K on the odometer (who knows what the actual mileage is), they were worn enough to cause compression loss. After having the guides replaced with phosphor-bronze guides (all the replacements are bronze) and having the valve seats ground, the engine runs like a top and gained about 50PSI in compression on the low cylinders. The last time I did a compression test, I was 380-415PSI in all cylinders. Like you I have no blowby (and I literally mean virtually zero) and have right at 1˚ of timing chain elongation. Not bad for an old engine. My turbo leaks oil, but that's a job for another day.

very encouraging , thanks for sharing, will keep posting,
 

very encouraging , thanks for sharing, will keep posting,

will look into head job,

140,000 miles ago,

compression was around 500 psi,

no wonder I got sad for half hour,

Compression on a NEW engine was ~450PSI. Getting 350-375PSI on a 300K engine would be doing very well. All things being equal, it should still run fine.

??? The valve guides aren’t in the combustion chamber.

Sixto
98 E320s sedan and wagon

exactly. 300 is fine. My old chilton says for reliable starting you only need 220 psi cold.

No they aren't, they're in the head and keep the valves moving in a linear direction. Let them wear out and the valves get sloppy and you get an egg-shaped wear pattern in the valve seat. The result is a poorly seated valve and subsequent leakage. All 12 valves were loose in the guides in mine, the wear was still early enough that the existing seats could be recut and stay within tolerance.

The engine must have been burning a quart of oil per tankful at that point.

Sixto
98 E320s sedan and wagon

injector one had oil on it,

Because I bought a lot of oil, at Costco,

did not pay attention, how oil is consumed,

planing to get a rebuild head, from Metric Motors, $1550,

are you saying you overfilled it a lot? I'd check other seals too if that's the case, too much oil with nowhere to go probably or could have blew out your other seals like the crank seals etc..