Date: Wed, 20 Jul 2011 08:47:38 -0500
Reply-To: mcneely4@COX.NET
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dave Mcneely <mcneely4@COX.NET>
Subject: Re: Watching Oil Temp (long, as usual)
In-Reply-To: <4e26317d.044b340a.74fe.ffff9e20@mx.google.com>
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---- Edward Maglott <emaglott3@GMAIL.COM> wrote:
> I think the hottest part of the engine is in the heads around the
> exhaust ports where all that hot gas is rushing past the valve and
> out. Aren't exhaust gasses 1300F+ degrees? The bearings have
> friction to produce heat but as long as they are lubricated I don't
> think they get that hot. I am curious and also appeal to those more
> expert than I.
Well, I'm not expert (the only expert I would consider such would be an engineer who works on internal combustion systems). I do believe that the exhaust gas heat is removed rapidly through the exhaust system. But you may be right that the pistons, cylinder walls, valves, and heads (especially the valves and heads) are hotter than the stuff down below. The fact that the coolant system has that big heat sink up front (radiator) means something, though. The oil cooler I referred to is an external, add on cooler like the tencentlife or similar one, not the little one that is stock on the waterboxer. 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. 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. The coolant has a large heat sink, and thus has a temperature gradient. That gradient includes the oil.
Again, experts may differ.
mcneely
>
> I think someone said earlier about the much greater ability of the
> cooling system to moderate it's own temperature. There is a big
> volume difference, about 4 times the amount of coolant to oil, and
> the big radiator and high volume pump. As the engine gets under load
> the cooling system can respond quickly and move a huge amount of that
> heat to the radiator and out of the system. The capacity of the oil
> system to remove heat is much lower. As someone else said, it's
> thermostat probably goes wide open and it does what it can but the
> smaller volume of oil flowing through the small cooler can only do so
> much. The oil system is designed to provide oil to bearings under
> much higher pressure and at lower volume. In general, the fact that
> it gets cooled one way or another is not primary. Many engines have
> no oil cooler at all (other than the sump.)
>
> I was changing my oil the other day and noticed how #%& hot the
> filter was after my short warm up drive. Made me wonder what the oil
> circuit is like. Sump to pump to stock cooler to filter to
> bearings? Or filter before cooler?
>
> Edward
>
> At 07:38 PM 7/19/2011, Dave Mcneely wrote:
> >---- Rocket J Squirrel <camping.elliott@GMAIL.COM> wrote:
> > > On Tue, 2011-07-19 at 13:14 -0400, Edward Maglott wrote:
> > >
> > > > I'm pretty sure the coolant flows through the heads and that is where it
> > > > picks up most of the engine heat.
> > >
> > >
> > > Oh -- okay. The only heads I've ever held were from an aircooled. They
> > > had no plumbing for coolant.
> > >
> > > So on the waterboxer, where is the oil picking up the extra heat that
> > > shows on the oil temp gauge but not the coolant gauge when the engine is
> > > under demand?
> >
> >The oil is picking up heat from all parts of the engine it is in
> >contact with, and that heat is reflected in the oil temperature
> >reading. The coolant is also picking up heat from all parts of the
> >engine it is in contact with. That heat is also reflected in the
> >coolant temperature reading. The two differ because the coolant
> >measurement is made at a point where the coolant is cooler than the
> >oil temperature. It would actually be a rather odd system with
> >absolutely equal heat distribution, especially since the coolant has
> >a cooler (the radiator) to reduce its heat burden. That is, there
> >is at least one point in the cooling system that is considerably
> >cooler than the heat source, the engine. Perhaps that is true for
> >the oil, also, especially if there is an effective oil cooler in the
> >system, but oil is less effective at heat transfer than is coolant,
> >and any oil cooler, though it might be a good one, is still less
> >effective than the very large radiator. Or, put another way, the
> >engine produces heat faster than the oil and coolant combined can
> >remove it, so there is a temperature gradient in the system. The
> >coolant is measured at the cooler end of that gradient. The oil is
> >measured at the hotter end. The oil is also directly in contact
> >with the hardest working, greatest heat producing parts of the
> >engine, the bearings, rods, cam and so on.
> >
> >my thoughts. experts may differ. mcneely
> > >
> > > -- RJS
> > >
> > > sent from my old aircooled heads
> >
> >--
> >David McNeely
--
David McNeely
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