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Date:         Sat, 8 Sep 2012 16:03:25 -0400
Reply-To:     Edward Maglott <emaglott3@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Edward Maglott <emaglott3@GMAIL.COM>
Subject:      Re: How does coolant circuit to oil cooler work?
In-Reply-To:  <504B8372.1010109@turbovans.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

Good explanation Scott. This diagram from Ben helped me to understand the 2 way nature of flow in the system. I agree it's very clever. One thing has always impressed me (and others) about the water cooled VWs is the impressive heater output. Not so much on my 2002 TDI. In the winter it takes a while to get warm. Once it's warmed, If I coast down a grade on the interstate, the temp gauge will actually drop off of the "normal" position. I think all VWs have that marked area at the cold end of the temp gauge. Don't drive it hard or use much heat until it gets above that level.

Edward

At 01:42 PM 9/8/2012, you wrote: >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


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