View original topic: Coolant lines cool/hot
charleslabri Mon Oct 26, 2020 11:42 am

Which side is cool (out) vs hot (in)?

And in the engine hatch, looking in from the rear of the vehicle, which side is which?
Ie hot feed on the left, cool return on the right.

MarkWard Mon Oct 26, 2020 12:10 pm

I recall inside pipe flows forward. Iíd have to double check.

VicVan Mon Oct 26, 2020 3:17 pm

Secondary source:

charleslabri Mon Oct 26, 2020 4:40 pm

This is super helpful. My Bentley is for aircooled.
Does that diagram have a description for this threaded inlet on the radiator, drivers side?

?Waldo? Mon Oct 26, 2020 5:02 pm

Considering you have a radiator and coolant pipes, you should probably get another Bentley. :wink:

That port on the radiator is for the fan switch.

VicVan Mon Oct 26, 2020 5:04 pm

This is for the thermoswitch.
It sets off the radiator's fan when the coolant gets too hot. My 1990 has three spades, (Ground, lo speed, hi speed) not sure what year you have, but you should have 2 or 3 spades.
I've just reused the one from my old radiator, with a bit of teflon tape (watch for the temperature rating of whatever sealant you're using).

Since you're working on your van's cooling system, I recommend this excellent article:

Vanagon Nut Mon Oct 26, 2020 5:09 pm

That threaded hole is for the rad fan thermo switch.

I wonder if mk2's uses the same switch connector and wiring gauge as Vanagons? Might be another source for those parts.

I find this website useful for searching parts, looking at diagrams:


Vanagon Nut Mon Oct 26, 2020 5:20 pm

On my 1981 air to water cooled swap I ran a new fused wire from battery to the 2 speed radiator fan circuits.

I'm guessing on this, but would suggest that connecting the rad fan circuits to the stock air cooled fuse panel might potentially surpass the amp capacity of the B+ (aka 30) wire from battery that powers the entire fuse panel.


charleslabri Mon Oct 26, 2020 7:06 pm

ok, good to know. I am running a derale 11" fan on a PWM, so I can set the temp sensor in there. Ill make a custom insert.
Looks like its brass, yah?

danfromsyr Mon Oct 26, 2020 7:41 pm

the proper switch that fits the hole and works as needed is like $9-$19.

I'd go with one of them. and yes it's the same bung on all H20 VWs of the era

Vanagon Nut Mon Oct 26, 2020 7:48 pm

charleslabri wrote: ok, good to know. I am running a derale 11" fan on a PWM, so I can set the temp sensor in there. Ill make a custom insert.
Looks like its brass, yah?

Might depend on radiator brand but that threaded hole in the rad you show looks like brass to me. I have a spare Behr rad I can look at.

I never measured or did the math re: total potential Amp draw through that OE 30 wire from battery to fuse panel. Not to confuse matters but thinking in hindsight.....

For battery to fuse panel, Bentley shows 6.0 metric for the 1985 and 8 AWG for the 1981. Looking online, they appear to be a similar size. That, and the fact that some early Vanagons c/w a gas heater (which IIRC took power from the backside of the fuse panel) indicate to me that one might be ok running a wire from the backside of the fuse panel to a Vanagon 2 speed fan. Not sure what your fan specs will be.

After headlight and engine upgrades etc., one issue I ran into on my '81 fuse panel was nearly running out of open male connectors at supply side of the panel; that thing is now "maxed" out in that regard.


danfromsyr Mon Oct 26, 2020 7:55 pm

I added a new power supply and new blade type fuse panel when I did my AC to H2o swap.
gave me fuses for the fog & driving lights and anything else I wanted really w/o getting into or dealing with the stock one..

charleslabri Tue Oct 27, 2020 10:28 am

Anyone have a clue as to the thread size and pitch there?
My thread toolkit puts it between m20-24 but doesnít get granular in there. Guessing itís probably m22

danfromsyr Tue Oct 27, 2020 6:19 pm

yeah it's the same standard they've always been.. from 1976 to at least 2006..

but if we have to look it up for you.. here it is I guess.,198...witch,4312

Temperature Switch
Fan Open/Closed Open
Fitting Thread M22x1.500
Terminal Pin Qty. 2
Style Temperature
Type Temperature
Connector Shape Rectangle
Meets / Exceeds OEM? Yes
Number of Terminals 2
Temperature Off 194
Temperature On 203

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