Date: Mon, 24 Dec 2001 15:42:11 -0500
Reply-To: Robert Donalds <bostneng@FCL-US.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Robert Donalds <bostneng@FCL-US.NET>
Subject: Re: Another operating temp question
Content-Type: text/plain; charset="iso-8859-1"
I wrote this a while ago and did a quickie edit for you reading pleasure
happy holidays
My experience with 2.0 air-cooled engines is limited to stock displacements, fuel injection and stock valves sizes. I would be hard pressed to change my ways because of the expectations that go with non stock engine configurations. the exception to this is a high lift cam with about the same duration as stock I started using these in the past year.
We tend to paint with a broad brush when we get into this conversation of engine temps. It is not one factor but many that contribute to the engines oil and head temps. In New England on a cool fall day it can take 45 minutes for the oil temp in my air-cooled vantage to level off if ever. Compression ratios do affect engine temps as does load, fuel air ratios, air temps, cooling fan intake temps, timing, RPM, road heat, the amount of time the engine is run and camshaft design.
I have spent time with digital temp gauges testing type 1 engines. The readings reflect the terrain and load in fact the graphs I made of head temps looked like a topographical map of the road I traveled on. my point is that the head temps swing widely much more than a slow to react cheap gauge will show. You cant say my heads run at any one number they don't. Oil is VERY slow to increase its temps above 225 F and in fact could be considered unwilling to go any higher unless forced. any increase above the 225F number means the head and piston temps are climbing at a much faster rate even if your head temp gauge tells you otherwise. where do you think the extra heat is coming from
I have seen head temps flash up 30 degrees F on the dyno in 1 second as the throttle is backed off and before the load is reduced that tells me the air flow at full throttle was responsible for the lower reading but that's not a real world happening how often do we drive at full throttle (unless you in a bus van climbing up a long grade) and how much heat would it take to make the reading rise 30 f in one second. The bottom line is I don't care what you head temp gauge reads. how hots the oil? The Gene Berg dip stick flickers at 225 F and that's a good thing to know
The use of external coolers with a thermostat is a good idea but does not always solve the common problem air-cooled busses and vans share that is to high a load for to small an engine with fuel that is not made to run in air-cooled engines with its higher combustion chamber temps. I find myself telling customers that the air-cooled engines have limits and those limits drop as the ambient temp goes up and are over all much lower than the good old days due to the fuels available
Running an oil cooler in the engine compartment warms the air in the engine compartment makes the intake system hotter reducing power and preheated the fan intake air does not cool the engine as effectively
.
I believe that VW used the stock cam design to warm the air-cooled engine up as fast as possible. The air-cooled engine needs all the help it can get to warm up on a cool day when the load is light and the time driven is short. This is to prevent the fuel from accumulating in the oil. The way the stock cam does this is with low exhaust valve lift of aprox .240 ths at the cam This keeps some of the hot gases in the head. For this reason I've started using a high lift non stock cams In the 2.0 engines. They drop the heads temps because there is no end gases left in the head. this lower head temp can be a problem for two reasons first is warm up time in the cooler climates as stated above takes longer and I don't believe lower head temps means lower piston and oil temps.
Bob Donalds
as always
all rights reserved
http://www.bostonengine.com
| 
