Date:         Wed, 20 Jul 2011 13:28:03 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Watching Oil Temp (long, as usual)
Comments: To: mcneely4@COX.NET
In-Reply-To:  <20110720094738.E3ACO.413851.imail@eastrmwml45>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 09:47 AM 7/20/2011, Dave Mcneely wrote:
>The cam and related apparatus do get really hot, or the oil would
>not get so hot, and the heat is generated by their action, not just
>picked up by transfer from up above.

I can't speak directly to the cam; however as of 1945 heavy
industrial journal bearings transmitting hundreds of horsepower
(propeller shaft bearings on an LCSL(3) landing craft with eight GM
8-71 engines on two shafts). ran at a working temp of about 135
F.  The rule of thumb was you could put the back of your hand on one briefly.

My strong impression is that exhaust heat is the primary contributor
to oil temps, and certainly oil is a major coolant for exhaust valves
and guides.  The intake valve is cooled by intake air, but the only
cooling the exhaust valve has is through the narrow contact ring to
the head, and through the stem.  Valves with sodium-filled stems have
a convection mechanism to help transfer heat from the head back up the stem.

>   And of course, the oil does lubricate the pistons and cylinder
> walls, which are right there where the exhaust gases (combustion
> gases) are generated.
>
>Bottom line, I think the oil has a major heat source, and only if an
>external cooler has been added does it have a real functional way to
>dissipate heat other than to the coolant through metals that both
>contact and through such things as the sump.  The sump is like a
>reservoir of liquid, it cools slowly compared to a radiator.

In our vans the sump is finned to aid in cooling, and of course
there's the external cooler on the 2.1l engines.  There's another
difficulty with oil, though, which is that its heat capacity is about
half that of water (but more than twice aluminum).

Dennis Haynes has determined experimentally that a major cause of
high oil temp in the WBX engine is frothing, which has led to his
recommendation to fill only halfway to the mark.

Yours,
David