Hi folks!  Glad to see many familiar faces (names?) here.  I have a question (see subject line) that I thought would be better posed here than on my normal haunt, the G-wagen board.  I tried searching, but surprisingly came up empty, even with "search all posts" checked....so here goes.

What are normal pre-turbo exhaust temperatures on a factory set-up 617a engine?

The one I have in my 1980 G now has been "tweaked" and I can bury the 1500 degree gauge (with pre-turbo probe) I have, if I'm determined to do so, but I know that can't be good.  I use a "drive by pyro" technique now and hold the temps below 1200, which does mean some downshifting on the long, steep grades I drive every day.  But I was wondering how even this compares with what the factory designed the thing to do.  I didn't have the pyrometer on this engine prior the recent tweaks, and the motor came to me used anyway, so heaven knows what was done before.

Any help would be greatly appreciated.

-Dave G.

1250*f is the safe limit for pre-turbo temperatures. The damage from high EGT's is not instant,
it's cumulative. The longer you drive with high temperatures, the higher at risk you become of long-term engine damage.

Did your engine start as turbocharged or did you add it on? 

Thanks for the reply! 

It's always been a 617a, a 617.950 variety (no EGR) to be exact, out of a '79 300SD, if I remember right.  Now fitted to my 1980 G in front of the 4-speed manual trans that's normally fitted to a 300 GD (normally aspirated 3 liter diesel in the G).

Sometimes if I travel up a long grade, holding temps to 1200 max, I get a "knock" developing after I've been going up with temps at 1200 for maybe 2-3 miles.  Taking foot off the accelerator gets it to stop after a few seconds, but it sounds ugly when it's happenning, like a ball peen hammer on the block that changes frequency (but not pitch or volume) as revs change with my foot coming off the accelerator.

If I run it up to 1200 in short bursts for a mile at a time or so, I never hear this.  There's just one particular hill where I get it.

Any thoughts?  Anyone experienced this?  I'm asking my mechanic to dial back the fuelling a little today to see if that helps, but I thought I'd run it by the folks here too.

Any idea what a bone stock 300SD runs for exhaust temps with the accelerator floored up a long grade?

Thanks!

-Dave G.

Thanks!  That's a great data point to have.

Mark dialed back the fuelling a little on Friday, both the full-throttle stop and the ALDA.  If the power is any less, it's not noticeable, and the exhaust temps seem to climb a lot more slowly, and stay lower longer on grades.  Tomorrow I'll try that long grade out of Denver on US 285 and see if the performance has changed at all.

I also went through the valves again yesterday and picked up a little better power, which lets me keep my foot out of it a little longer on the grades.  More about that in the valve adjustment thread.

-Dave G.