Date: Tue, 19 Jul 2011 09:27:13 -0700
Reply-To: Don Hanson <dhanson928@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Don Hanson <dhanson928@GMAIL.COM>
Subject: Re: Watching Oil Temp (long, as usual)
In-Reply-To: <1311087322.26578.91.camel@TheJackUbuntuNetbook>
Content-Type: text/plain; charset=ISO-8859-1
On Tue, Jul 19, 2011 at 7:55 AM, Rocket J Squirrel <
camping.elliott@gmail.com> 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
>
What's happening is....the oil circulation flow remains the same always
(varies speed with rpm, but not volume with temperature). Your coolant flow
is increased or decreased (the volume of flow) by your thermostat. So...as
the bigger loads create heat, your coolant flow increases because your
thermostat opens in response....and more coolant is passed through your
radiator and loses the heat at an increased rate. Your oil, on the other
hand, that flow remains relatively constant, no matter what the load, no
matter what the temperature.......more load=more heat...same flow, more heat
accumulated. Your coolant temperature gauge is measuring and indicating the
temperature of the coolant. Your oil temp gauge gives a better indication
of the temperature of the whole motor, I think...
I don't think the thermostats used in oil circulation cooling systems are
nearly as 'modulatory' (I made that word up) as the ones in our cooling
systems, not as wide-ranging. Most oil thermostats simply open or close,
rather than vary the flow..Most open at around 180f..
Mine (oil temp) climbs to about 220f (the oil) on fast ascents of steep
grades..my coolant temp stays just below that LED...whatever the coolant
temp that actually may be.
Oil circulates to near all the moving parts and takes it's temp from very
important stuff like the main bearings and the block...so I pay attention
primarily to my oil temp.. The coolant system on a vanagon seems adequate,
if all works properly, to keep that temp under control...
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