Date: Tue, 19 Jul 2011 07:55:22 -0700
Reply-To: Rocket J Squirrel <camping.elliott@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Rocket J Squirrel <camping.elliott@GMAIL.COM>
Subject: Watching Oil Temp (long, as usual)
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I just completed the wiring to my swell new gauge cluster: oil pressure,
oil temp, ATF temp (okay, not yet hooked up), engine/cabin battery volts
(they are on separate charging systems so being an electrical geek I
like to be able to monitor them both), and tach).
This will be the first time I've ever had a vehicle with an oil temp
gauge!
So I'm watching the gauge to learn how oil temp responds to driving
conditions. Once the little thermostat thingy in the oil filter banjo
adapter's bypass opens up and oil starts being sent to the heat
exchanger, the gauge rises up to about 180-185F and pretty much stays
there under light town driving. The coolant temp gauge in the van's
instrument panel shows a steady temp, too.
So last week I'm heading out of town on the highway, up a grade, into a
headwind, and pushing pretty hard. Excited to be going on a camping trip
to a new site.
What I saw was that while coolant temp continued to stay constant, oil
temp went up -- 195, 200F. The engine's working harder, okay. But here
the coolant temp gauge says that the cooling system is keeping up with
the demand while the oil temp says otherwise.
Obviously, then, the senders for the two temp gauges are seeing things
differently.
So here's what I'm thinking, correct me if I'm wrong:
Oil temp and coolant temp decouple under high engine demand, and that
while the cooling system is capable of keeping the portions of the
engine that the coolant is in intimate contact with cooled, the oil is
in contact with portions of the engine that the coolant doesn't reach
and which are close to the combustion action.
So where is this? My first guess is the heads. The coolant surrounds the
jugs, but not the heads, which are part of the combustion chamber and
where oil flows over the hot valve stems.
The oil temp gauge reports the temperature of hot oil returning from the
heads mixed with general overall engine oil temp, so therefore it's not
an accurate indication of peak oil temp. And that's why people install
CHT gauges, to get a better picture of what's going on in the heads.
This is my initial interpretation of what I'm seeing.
--
Rocky J Squirrel (Jack Elliott)
'84 Westfalia: Mellow Yellow ("The Electrical Banana")
'74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
Bend, OR
KG6RCR