Date: Fri, 19 Nov 2004 22:25:41 EST
Reply-To: FrankGRUN@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Frank Grunthaner <FrankGRUN@AOL.COM>
Subject: Re: [Diesel-Vanagon] On Oil Coolers,
Cooling System Design and Engine Life
Content-Type: text/plain; charset="ISO-8859-1"
Andrew,
When I slog out these missives, I often get interrupted and lose a train of
thought. My comments to your questions and interspersed with your post below.
I'll start them with a $$$ in recognition of the cost of this hobby!
> I would like to say that I thoroughly appreciated your post to the
> diesel-vanagon group regarding the vanagon cooling system. I only read it through
> once, and that was after a very hard day of work, an empty stomache and a
> beer. I will reread it tomorrow. I did have a couple of questions that you
> might care to answer.
> I assume from your post that the waterpump drives the coolant constantly
> through the stock oil cooler. I assume from the hose routings that it drives
> the coolant through the cooler from the top radiator hose to the bottom
> radiator hose. Is that correct?
>
$$$ Not true. The water pump is constantly applying pressure to the inlet
side of the cooler, but the outlet in the vanagon circuit is connected to the
thermostated return. (On the Quantum TD and Later G/J models, the oil cooler
coolant return is connected to the heater return line to the pump. Unthermostated
and on all the time.) Therefore, vanagon case, the cooler only flows coolant
when the thermostat opens. The flow is given by pressure. The coolant coming
out of the block at the main cylinder head port and the heater port have the
maximum pressure and the inlet ports at the water pump have the lowest pressure.
The cooler has the same flow regardless of orientation. In the archives of the
vanagon list, you can find my measurements of peak oil temperature with and
without the stock cooler and the RX-7 external cooler. I believe that the stock
unit was good for a 35 F reduction in peak temperature. Could be wrong.
Definitely significant.
> I would also assume from your post that after the engine has reached
> operating temperature that the engine oil flowing up through the oil cooler is
> always hotter than the engine coolant also flowing through the stock cooler.
> Is that correct?
>
$$$ Definitely true. Although the coolant always reaches its steady state
operating temperature faster than does the oil. A lag of 15 minutes in town
operation is not unusual. BTW, my diesel vanagon experiments showed significant oil
temperature differences with and without the sound shield in place. The
surface of the aluminum oil pan is a considerable heat exchanger in its own right.
> If my assumption regarding the flow of the engine coolant through the
> cooler is correct, then why is it returned to the block without being cooled?
> Just for simplicity?
>
$$$ Confusion. This is true for the Quantum and G/J configurations mentioned
before. This would increase the percentage of coolant involved in the bypass
circuit. The purpose of this circuit is to provide flow to eliminate cavitation
at the pump impeller as well as boiling of uncirculated fluid in the
block/head. The tubing leading to the cooler has flow restrictors built-in. These
minimize the flow to a probably insignificant level. Knowing the VW engineering
approach, I would expect different flow restrictors for the oil cooler feed
plumbing for the vanagon and G/J cases. Small reduction of cooling capacity,
unless you bypassed the VW hose group and plumbed it up without restrictors. Then
capacity loss could be serious. I would never accuse VW of simplification.
> I believe that I originally started this ongoing discussion in the
> diesel-vanagon group by posting the idea of stacking two of the stock coolers in
> order to increase the heat transfer. Any reason not to do so?
>
$$$ As I said, I'm using two stock coolers in parallel (oil perspective,
series from the point of view of coolant flow). I will use full size hose
connections between the two and measure the difference in flow at 15 psig. If the flow
restriction has significantly increased, I will open the restriction orifices
the reestablish the correct flow. My circuit will go to the thermostated
inlet port through the auxiliary water pump. As to not to stack coolers ... you
must be careful about the o-ring seal. the stock cooler traps an o-ring between
its top surface and the face of the oil filter stand. The lower surface seal
of the cooler to the filter is maintained by the filter gasket. To stack
coolers you need to take care over the second o-ring retention and fabricate a
longer stand center pipe. You probably need to make it a fully threaded piece to
add the retaining bolt for the first cooler. Dangerous the put all the force
requirement on the last nut at the end of the second cooler. Other than that, why
not.
> Can you see any reason the designers opted to run the lower hose from the
> oil cooler to the lower radiator hose? It would seem to heat the oil to
> operating temperature faster if there was flow though the cooler before the
> thermostat opens. Perhaps the thermostat opens fairly quickly, but as the
> coolant from the cooler is returned to the waterpump one way or another I can see
> no reason to delay the flow through the cooler.
>
$$$ Thermostat is good. More bypass will slow heating rate of engine coolant.
Thermostat begins to open in less than a minute in SoCal. NBD. Besides
thermal transfer is more efficient at elevated temperatures. The difference in even
5 minutes to the opening of the thermostat is irrelevant. Heat up block
coolant to operating temperature ASAP, then get the oil up to speed, then moderate
viscosity reduction on the part of the engine oil.
> Is there any reason not to reroute the lower oil cooler hose to the heater
> return to the waterpump?
>
$$$ Could have an air bubble trapping impact since it reduces the flow of
startup coolant through the expansion tank. But not a biggie as long as you stay
to VW flow restrictions.
Frank Grunthaner
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