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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