Date: Sat, 19 Nov 2005 04:30:07 EST
Reply-To: FrankGRUN@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Frank Grunthaner <FrankGRUN@AOL.COM>
Subject: Comments on the Oil Cooler Upgrade Issue
Content-Type: text/plain; charset="US-ASCII"
I've just noticed the exchanges on upgrading the oil cooler (ne heat
exchanger) and thought I would add a few comments.
As has been pointed out by several, the oil-to-water heat exchanger serves
two very important purposes: 1)heating of the oil to proper lubricity
temperatures first (important in all climates and very important for short city
commutes. More important for diesel engines than for gasoline engines, and more
important for turbocharged engines than for N/A units. Extensive public and
professional publications on this. See the tech paper archive on Alistair Bell's web
site for some of the VW tech material. Effects longevity and fuel efficiency.)
and 2) cooling oil in high load applications.
Deleting the oil to water exchanger and substituting an oil to air unit is a
bad idea. As a minimum, the startup to full operating temperature period will
be extended, bearing wear will be significantly accelerated and the level of
sulfuric acid in the crankcase will be enhanced. Subsequent hard operation with
turbo or N/A can burn off the sulfur oxides, but this takes a significant
time depending on the water in the crankcase and the extent of aeration.
However, the second function (capping the maximum temperature of the oil)
does depend on the excess heat injected into the oil by the engine and the
thermal capacity of the heat exchanger. Note that for all north american VW engine
models of 2L or less, turbo or N/A, all use the same size oil to water heat
exchanger. This includes the 1.8 turbo and the VR6. However for higher output TDi
engines in Europe two larger size heat exchangers are available. The size of
the largest one has about twice the exchanger surface area as the standard
one. This is obviously to control the upper temperature point of the oil,
holding it closer to the coolant temperature. The details of the rate of heat
transfer from the oil to the water are such that as the oil temperature goes up,
more surface area (or transfer time) is needed to fully equilibrate the
temperatures of oil and water.
Now, one of the highest thermal output engines sold in north america by the
VAG group is the 5 cylinder turbocharged WK and MC engine used in the 1981-88
Audi 5000T. The WK engine used a dual oil filter adapter off the engine block
with an integrated thermostatically controlled external oil cooler. The MC
engine used a single oil filter version of the same adapter flange again with the
thermostatically controlled external oil cooler. As I have indicated in other
posts to the Vanagon list (many reproduced at Alistair's site), in my TDi
conversion and in my Turbocharged Audi 3A engine build, I have fabricated an
adapter to use the dual oil filter assembly on the oil filter flange. In the Turbo
3A build, I used the dual oil filter adapter with two standard oil to water
heat exchangers (one on each oil filter leg) and an external oil cooler (used
the Audi 5000T unit). For details, see the vanagon list archives.
For my TDi conversion, I used the dual filter adapter from the Audi 5000T
again, but upgraded the capability further. First, I procured a Euro spec Audi
1.9 TDi oil filter flange (same as the Passat TDi) that is angled towards the
transmission as is appropriate for longitudinally mounted engines. I then
mounted my adapter and the Audi dual filter flange. I then procured (during my
European travels) one of each of the higher capacity VAG oil to water heat
exchangers and mounted them on the Audi oil filter flange between filter and flange.
Fit just fine. I then plumbed the external oil cooler for the passenger side
duct as I described previously.
The net effect of these mods is surely excessive, but I'm building for
reliability. The high surface area heat exchangers (about 3.5 times the standard
unit surface area) should bring the oil temperature up to coolant temperature as
soon as possible. Note that the coolant flow path through the heat exchangers
is designed to do this rapidly without waiting for the full heating of the
coolant in the radiator loop. The upper temperature on the oil during heavy turbo
boost and low rpm may well be controlled by this excess coolant capacity. As
a backup, however, the external cooler (never in the circuit until full
operating temperature is reached - about 172 degrees by my measure) will hold the
maximum oil temp below 230. Actually see the oil temp staying within 5 degrees
of the coolant temperature under all test conditions to date. The dual oil
filters add an extra measure of capacity and the whole system adds about 1 quart
to the oil sump volume. I use the same braided stainless lines to the external
oil cooler as were used by Audi. The whole system is rather inexpensive using
readily available salvage parts.
I use the same flow circuit used for the JX motor with a thermally switched
auxiliary coolant pump adding to the recirculation head in the heat exchanger
circuit. The aux pump is also triggered for run-on after engine shutoff.
Couldn't use the high filter capacity Volvo 6-cylinder turbodiesel oil filters on
the leg near the A/C compressor because of clearance problems.
Finally, on the issue of flow direction through the heat exchangers, remember
that the Vanagon coolant system is heavily overcooled for engine size and
power output (for detail see Vanagon list archives). The circuit functions on the
same rapid warm-up design as used for the heater. Quick access to head heated
coolant.
I went to this level of effort for reliability. In my TDi conversion, using a
1Z base engine with the VNT turbo and manifold, larger injectors and a stage
2 RocketChip tuned to Euro AFN specs, I wanted to minimize oil breakdown
effects. I'm using synthetic oil, a windage tray, baffled oil pan and the
aforementioned oil cooling circuit mods to ensure that operating oil temperatures hit
180 ASAP and don't exceed 230 under any load condition including full A/C
power, 120 amps from the alternator, upgrade acceleration at 75 mph, engine rpm
between 3500 and 4400, and traveling through west Texas on the 4th of July!
Just my 2 cents,
Frank Grunthaner
