Date:         Mon, 15 May 1995 14:10:26 -0700 (PDT)
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         David Schwarze <schwarze@superc.nosc.mil>
Subject:      Re: Overheating

Dave Kautz writes:
> 
>  All this talk about overheating has piqued my curiostity <again>. Could
>  someone who has both a cylinder head temp and an oil temp gauge comment on 
>  the relationship between the two. When the engine gets hot, do both temps
>  move up together? Is oil temperature more affected by engine speed <increased
>  friction> than head temp? Do the heads ever get really hot but the oil stays
>  closer to normal?

My experience is this.  I'll be driving along the highway, oil temp about
210, CHT about 275 (mine is measured at the boss - spark plug readings
seem to be higher for other people).  I'll see a grade coming, start up
it in 4th.   Gas pedal almost (but *never* fully!) floored, try to hold
speed at 55.  At this (relatively) slow RPM, the oil temp will remain
close to the same for a long time, while the CHT will rise very quickly
to around 325.  If I downshift and slow to 45 in 3rd, the rpms go up a lot,
and the oil temp shoots up very quickly while the CHT drops to cruising
temps (275-ish).  If I maintain high RPMs in 3rd, the oil temp will go
through the roof.  Once it hit 270 - never again.  So, I generally slow
down to 40 in 3rd to get a good balance between oil temp and CHT.  Once
the oil temp is this high, it will not go down easily, and if I try to
shift back into 4th at 50mph, the pressure is very low, like 20-25psi.
This while the oil temp is hovering around 240.  I ran (until 2 weeks 
ago) Castrol 20-50 for all of the above tests.  I ran straight 30 weight
for a while, but found that pressure dropped, and went back to 20-50.

Two weeks ago I put in 15-50 Mobil One synthetic.  I haven't been on
any long drives yet, but yesterday driving up a grade I got the temp
up to 230.  From what I can tell, the oil temp hasn't changed much, but
pressure seems to be up a little at high temps.  Not a lot, but even
at 230 degrees I still had 40psi @ 60 mph, which I consider to be
good pressure.  I think I will stick with the 15-50 synthetic, since
(fortunately) my bus doesn't use any oil.

>  And finally, what temperature do people call "overheating"? Oil temp at 250
>  degrees? Heads at 400 degrees? 

My VW performance book states that ideally oil temp should be between
180 and 230, and never exceed 270.  Don't know about CHT.

-David

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David Schwarze                     '73 VW Safare Custom Camper  (Da Boat)
SAIC Comsystems, San Diego Calif.  '73 Capri GT 2800            (Da Beast)
e-mail:  schwarze@nosc.mil         '87 Mustang Lx 5.0           (Da Sleeper)
http://papaya.nosc.mil/~schwarze   '93 Weber WG-50              (Da Piano)
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