Date: Tue, 19 Jul 2011 08:14:33 -0700
Reply-To: Alistair Bell <albell@SHAW.CA>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Alistair Bell <albell@SHAW.CA>
Subject: Re: Watching Oil Temp (long, as usual)
In-Reply-To: <1311087322.26578.91.camel@TheJackUbuntuNetbook>
Content-Type: text/plain; charset=us-ascii
Saw the same thing in my '82 with I4 gas...
high rpm, high speed - oil temps up, coolant temps ok
mod rpm - mod speed - all ok
mod speed, mod rpm, high load (hill) - both temps up
mod rpm, slow speed (climbing steep hill, gravel) - coolant temp up, oil temp up a bit
high rpm, low speed, high load (steep gravel roads, switchbacks etc) - coolant temp up, oil temp up
alistair
On 2011-07-19, at 7:55 AM, Rocket J Squirrel wrote:
> 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
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