Date: Tue, 25 Dec 2001 10:24:04 EST
Reply-To: NotaJeep@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Steven Denis <NotaJeep@AOL.COM>
Subject: Re: Operating temp question/Boston Bob's solution?(long)
Content-Type: text/plain; charset="US-ASCII"
In a message dated 12/23/01 6:19:30 PM Eastern Standard Time,
developtrust@HOME.COM writes:
<< I always thought running cooler was a good thing, but then these VW systems
are so new to me that I just am not convinced of anything yet. >>
OK.. The ability to reject waste heat is the important part. there is an
optimum temperature for your engine based on it's design (materials,
clearances, etc)
Really we'd LIKE to see an engine that HAD no waste heat...You will see
ceramics used in engines so that you can have operating temperatures
ELEVATED!. In an Otto cycle engine there is no such thing as "too hot"..
HOWEVER we are talking your pride and joy here, not some theoretical "paper"
engine.
SO...Let's say that the WBX engine is designed to operate at a coolant
temperature of 220F. (and that can and does vary throughout the system.this
220 is the temperature at the measurement point.IE: the sender)
This temperature was used as it's as hot as they dared run the engine (with a
built in margin for safety) to get the benefits of better combustion without
causing a loss of reliability and durability. I'll not bore you to tears with
combustion theory with "skin gases" and "end gases" and how cooler internal
parts quench combustion and absorb the heat that you'd LIKE to be using to
force the piston down OR how quickly the strength of common materials drops
off past critical temeratures..No, I'll just say that the cooling system
temperature is a compromise. One of the major problems that you face is not
really the ring/cylinder wear due to liquid fuel..what the BIGGEST problem
would be is oil dilution. Oil gets ruined, and FAST, by NOT GETTING HOT
ENOUGH!..Yep too cool is bad..one of the byproducts of combustion is
water...water that DOES end up in the oil. IF the engine does not warm up
enough or LONG enough, this water is not vaporized and removed by the
crankcase venting system...This is why the owners manuals for most cars tell
you that short trips/cold weather operation will require more frequent oil
changes...
So...You need to make sure that the system is clean (garbage insulates) and
full (leaks are bad) and that the thermostat is correct (like the right type
and temperature range) and then it's REAL HANDY to have an
accurate/relable/FUNCTIONING warning system for temperature and coolant loss.
Notice I said "handy" not critical..the system SHOULD be automatic and
function with no care on the part of the driver..It's not like you need to be
opening valves or closing radiator shutters to maintain the correct
temperature. No? hey it USED to be that you had a spark advance lever on the
steering column so that you could adjust the spark timing to suit the
temperature,fuel and road/load conditions...Now you have automatic spark
advance and COMPUTERIZED (woo woo!) engine management...How can you let a
machine deal with something as critical as spark advance? ..you design a
simple and reliable system and you let it do its job. The cooling system is
actually simpler to make than a spark advance. However...it is more subject
to environmental damage and catastrophic failure than the spark timing.
I hit a deer one time with an International Harvester Road Commander (aka
"Road Commode") I was fully loaded with a 40ft trailer..."Bambi" didn't stand
a chance and the remains spun off well into the median..Stop and check?..heck
no!...the IMPORTANT gauge for the next few minutes was the temperature...It
didn't climb so the radiator was undamaged and, really, that's what counted.
The cylinder head etc, even on that POS, cost more to replace in parts labor
and down time than a new syncro westy..So between the tach and speedo were
BIG oil pressure and coolant temperature gauges and warning lamps..and
BUZZERS!..Anyone with even a vestige of hearing would notice something was
wrong when either buzzer went off..it rattled your filllings....
So...make sure your system is in good shape and THEN make sure that the
warning system works correctly.
And then leave it alone!
As for "fooling" the computer to richen the mixture. Once the engine goes
into "closed loop" with the oxygen sensor working correctly, all the"fooling"
in the world is not going to help. The oxygen sensor will see the "rich
mixture" and adjust it back to where the computer thinks that it's supposed
to be.. The "map" in the ECU needs to be reprogrammed to provide the proper
fuel mixture. I would THINK that the PROM chip that is available would do
exactly that...but Bob's tests prove otherwise...interesting indeed.....
A quick test would be to unplug the sensor and see what happens. The system
defaults to "open loop" and a preprogrammed set of parameters. (this
temperature, this air flow, this RPM?..Hmmm it gets THIS amount of fuel...)
IF you were to change the setting of the fuel pressure or airflow sensor or
the temperature sender, then you could vary the mixture and the computer
wouldn't know.
steve...
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