Date: Sat, 8 Sep 2012 10:42:10 -0700
Reply-To: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Subject: Re: How does coolant circuit to oil cooler work?
In-Reply-To: <1347073071.83291.YahooMailNeo@web163402.mail.gq1.yahoo.com>
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Perhaps something not being considered is the two door nature of the
thermostat.
When the main opening for rad flow is closed, the other part, for flow
in the bypass hose is open.
that way.....when coolant is flowing out of the side connection on the
cylinder head ....it's trying to flow through the oil cooler to the main
return hose going to the t-stat...
but it can't since that main portion of the t-stat is closed.
Similarily, it can't flow through the oil cooler either , as that
coolant will run into the closed main opening in the t-stat also.
Meanwhile, before the t-stat is open ...coolant runs around and around
through the bypass hose ...
from inside the cylinder head, where coolant is under slight pressure
from the water pump....through the bypass hose, and back into the water
pump housing ..around and around.
gradually the t-stat closes off the bypass circuit and opens the main
circuit ..
thus allowing coolant flow to the radiator and through the oil cooler.
Given the relative size of the hoses ..
the inside cross sectional area of the main radiator hoses and pipes are
3 or 4 times larger in area than the inside of the oil cooler hoses and
fittings ..thus 'most' hot coolant will be pushed to the radiator and
eventually routed back to the thermostat inlet.
Quite clever. Means no flow through the oil cooler cirucit when things
are cold,
and 'some' ...like 1/3 of 1/4 of what's coming out of the side outlet on
the cylinder head, through the oil cooler when hot.
and yes....as the main circuit starts to open the warm coolant also
helps to warm the oil ..
so the oil cooler is a heat exchanger helping to warm the oil at first,
then later, to help cool it. Very clever and always a good addition to
any engine really. Other than the cost of the part, it's a 'free'
improvement affecting engine longevity in a good way.
if it's not clear to some people ...the heater circuit is 'full time
flow' .... the hottest coolant in engine would be that coming out of the
cylinder head. If the heater valve is open ...there is un-thermostated
full flow in the heater circuit.
And ..in winter .......it's not good to start out with the heater full on.
This cools the engine enough that it takes much longer to get to full
operating temp. What works is to have heater mostly off, of fully off,
for say the first 4 miles or so ..then turn it on some.
Diesels to not produce much heat without a load. If your winter
driving mode is a long down hill run ..
that's exactly what you don't want. Ideally ...you start out with some
load ....level or slightly uphill .....keep heater off for a while, or
at least half off ..then as things get warmish, open the heater valve.
It doesn't matter too much, and I'd say it helps to think of the
water pump as pushing coolest,
and not sucking. Water pumps push coolant.
some might find this interesting ..
why I had to think about this so hard in the first place once. On jetta
cars the oil cooler is fed from a T in the bypass hose on the engine.
So I'm doing an AAZ conversion to a Syncro Doka ..and that T'd bypass
hose is already on the engine ...
so just leave that there, and the return from the oil cooler..
hey, return is return right ? So I use a stock DV main coolant hose
that goes to the T-stat., with the oil cooler return T'd into that as
per stock DV.
The rig overheats in about 20 minutes of driving on the level., or
gets too hot.
That's when I had to really, really look at what flows where and when..
On a DV the oil cooler return is to the main hose going to the t-stat.
on a jetta it T's into the heater return hose.
Either layout works just fine, but you can't mix 'em.
By using the DV return to the main t-stat hose and oil cooler feed
from the bypass hose, coolant was bypassing the radiator and t-stat
through the oil cooler ..which is why it overheated in a while.
what fun !
Scott
www.turbovans.com
On 9/7/2012 7:57 PM, Poppie Jagersand wrote:
> Help explain to me how the oil cooler gets circulation. Here's what I can see, but don't understand exactly how it works:
>
> The oil cooler on a Vanagon Diesel is connected to the coolant loop in two places:
> 1. At the radiator return hose near the pump.
> 2. At the radiator hose from the head to the radiator.
>
> What puzzles me is how it works. Just looking at the hoses this is what comes to my mind:
>
>
> When the thermostat is closed it seems to me that there is no flow from rad to pump. Does this mean also no flow out of oil cooler? Or how is the flow to the cooler routed.
>
> When the thermostat is open then it seems like the pump would suck warm coolant from the top of the block, through the oil cooler and then to the lower rad hose and into the water pump. This to me seems like a short of the loop to the radiator, meaning water that should go to the radiator them the thermostat is open can instead bypass the radiator and go throught he oil cooler. This would have two bad effects: 1. Less water to the rad means less total engine cooling, 2. Hot water to oil cooler instead of (suitably cold)
>
>
> Is that really how it works?
>
> Experiments I did contradicts the above, Hence my question. I put a temp sender on the *output* of the oil cooler (not the norma sender location but sender is on the middle oil pipe that goes to the turbo on my AAZ 1.9TD) The oil cooler output temp stays low even when the head is very hot (so I can have 90-100C oil to turbo even when head is 110C) This is of course a good result that the oil cooler cools, but I just don't understand how the coolant is routed and regulated to keep the oil temp constant. (Too low oil temp would also be bad in the winter)
>
> Anyone has a good explanation?
>
> Thanks,
> Martin (and Poppie 1.9TD Westy)
>