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TDI Conversions Discussions on converting non TDIs into TDIS. More general items can be answered better in other sections. This is ideal for issues that don't have an overlap and are very special to swaping engines.

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Old November 12th, 2019, 07:07   #1
AndyBees
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Default Coolant flow in your Conversion set-up

As many of you know, I did an ALH TDI install in an 84 Vanagon (http://forums.tdiclub.com/showthread.php?t=276798) which was finished and put on the road in August, 2012 (about 84k miles on it now).

So, I've noticed the engine temperature runs a bit on the high side during cold days. Observation is via Scan Gauge as well as two on-dash temp gauges. One gauge is an aircraft grade and the other is a McNally EGT/Coolant temp combo. This temp increase is nothing new but with cooler weather upon us, I've been reminded.

Anyway, this is my theory on why the engine temp may be increasing during cold weather. But, first, in case you are not familiar or have not given it any thought, circulation of the coolant in VW engines is somewhat complicated. Coolant leaves the engine at the end of head next to bell housing thru the coolant flange and one small metal pipe down below the coolant flange.

From the coolant flange, one hose goes to the EGR/Heater circuit, one hose goes to the Oil Cooler and the big hose goes over to the top of the Radiator. From the one small pipe, coolant flows to the top of the expansion tank .......... for the moment forget about the coolant flow to the Radiator (big hose). So, coolant from all those circuits flows back to the Water Pump housing via a single black metal pipe. That coolant, when hot enough, is what activates the T-stat which is mounted in the side of the WP housing (which is where the return coolant from the Radiator enters). If that coolant stays below the opening temp of the T-stat, it doesn't open.

So, back to my Theory on why the engine tends to run on the hot side in winter. With my set-up the coolant that circulates to the front of the Van where the heater is located is through at least a 32 foot long loop. Thus, by the time it goes to the front, thru the heater and returns to the Water Pump housing it is, in effect, only lukewarm. This coolant, even when mixed with the hot coolant returning from the Oil Cooler and Expansion Tank, is too cool to open the T-stat, but hot enough to increase engine block and head temp. The McNally temp sensor is on the coolant flange and the aircraft temp gauge sensor is on the return hose from the Oil Cooler......... and, they both show the temp increases. And, the OE coolant temp sensor is on or at the coolant flange and it shows the temp increase via the Scan Gauge......

Oh, and I eliminated the EGR Cooler circuit when I did the engine conversion.... not sure if this has anything to do with the heat differences.

So, what's your thoughts on this?

With your conversion project, have you noticed or had a coolant temp issue?
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Last edited by AndyBees; November 12th, 2019 at 07:10.
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Old November 12th, 2019, 08:23   #2
eddieleephd
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Your issue I believe is complicated by water from the radiator mixing with the warm coolant entering the engine.
Your assessment of the situation makes sense. It almost seems as if you should also use an auxiliary electric circulation pump to move it faster. The other option is to reduce the thermostat temp range.
I've considered the thought of creating a dedicated coolant line to warm the cab of a van that wraps around the exhaust and uses an electric circulation pump.
Toyota uses a valve in the coolant line to stop the circulation into the car when the heater is off. One could be used to limit the flow through, or from, the coolant circuit to the cab.

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Old November 12th, 2019, 12:16   #3
d24tdi
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OP, I think what you are theorizing is right on the money. This same effect is a known problem in Subaru engine conversions into Vanagons and is probably equally troublesome in your situation.

The Subaru EJ engines use a similar cooling system concept to these VW inline engines, with the tstat mounted low in the engine at the inlet of the lower (cold/return) radiator hose, and with the heater circuit return also entering at the tstat housing but on the engine side of the tstat and the heater return flow aimed right at the tstat pellet. In a Subaru with short heater hose plumbing and only one heater core in a small interior cabin space this works fine, but in a Vanagon, running two heater cores in a large cabin with yards of heater hose plumbing, operating in cold weather while using full heat was causing Subaru converted van owners to see elevated engine operating temps just like you observed. The cause is the thermostat being "tricked" by the very low temperature of the return coolant from the heater circuit and as a result not opening sufficiently, even though the rest of the engine was running above operating temperature.

Here's what the solution looks like that many of the Subie swap folks use: http://subaruvanagon.com/tom/Thermostat%20housingk.htm It is a spacer that goes between the thermostat and water pump and allows a small amount of coolant to recirculate directly from the heater circuit outlet at the engine (IOW, hot coolant that is at full engine temperature) and reach the tstat pellet. This allows the tstat to respond to the actual temperature of the engine rather than the cold coolant returning from the heaters.

Something similar might work for the TDI engine, or you could try to find a different/less direct routing for the heater return so that it doesn't affect the thermostat as severely.

I don't think you would want to put a heater control valve or restrictor in the heater circuit, since although that might succeed in keeping the engine from running hot, it would also reduce heater output which is probably already less than you would like, in TDI tradition.
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Old November 12th, 2019, 18:15   #4
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Thanks guys! Your thoughts match mine.

I had to go into town tonight (about 28 miles round trip). So, I watched the gauges very close. It is 22f outside. So, the engine temp got up to a little over 205f with the heater on full flow and 2nd speed on the fan selected... So, on the return trip, I shut-off the coolant flow to the heater.. In about two minutes, the coolant gauges began to drop to normal, including the temp shown on the Scan Gauge.

So, I suppose the issue is now clearly identified ....

I'll look into what the Subie guys have been doing.

Thanks
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Old November 12th, 2019, 18:50   #5
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Not sure what temperature thermostat you're running, but, I noticed a while back that anything other than the highest temp thermostat had a couple holes in them allowing coolant to flow all the time.
In my experience it caused longer warmups and could contribute to your issue.

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Old November 12th, 2019, 19:03   #6
eddieleephd
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The first link shows the Mahle 87* thermostat without holes and the second shows a brass piece on the left indicating it has a plugged hole which likely let's coolant flow a little. It's small, however, makes a difference. I figured it out first on an old Cummins I had. Just a thought to keep in mind.

87*
https://roselandtech.ca/thermostat-alh-bew-bhw

180*
https://shop.advanceautoparts.com/p/...hoCZu8QAvD_BwE

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Old November 14th, 2019, 05:04   #7
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Default OverTemp Van-Again

Why not insulate the long runs of heater hose?
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