How works a vw thermostat (long read, data heavy)

[ALB]

Great info and thanks so much for posting this (and the mega thought and effort behind it). Love the intercooler air temperature gauge (very innovative)! It would be interesting to see what happens if you also duct air into the engine compartment from in front of the engine (under the car and ducted through the front breast plate). I'm guessing under hood temps will drop noticeably and all temps will become more stable. Al
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[Bad bug]

[Alstrup]

One thing you should do first is to cover the vents in the decklid to mimic an early engine compartement and get data from that, both with closed and with the tennisball.

I will say though that when we did similar tests 20 years ago we did´nt see much gain with the tennisball trick with a vented lid. With an early lid without vents it was a different matter all together.

Also, the faster you go the lesser gain you will see with the tennisball trick due to hot air turbulence behind the car.

4-5 2" holes behind a 3/4" raised licenseplate on an early non vented lid improves air intake with about 3%.
Early vert vents in a 60-67 lid gives almost the same results as a vented late lid.
60 - 69 vert vents and 4-5 2" holes behind the licence plate gives almost the same results as a late sedan vented lid.

A late vert lid with the Mexico flaps under the licence plate light is the best stock decklid you can get, followed sharply by the Mexico sedan lid.

With fan shrouds. There is´nt that much difference between a GOOD aftermarket 30 hp shroud and a late carburetted shroud. The addition of the venturi ring improves air intake with up to about 5%, rpm related.
the late style venturi ring doesn´nt work on aa early shroud (12/13/1500) It creates an unwanted turbulence that I for one have not been able to elliminate. There you need a Porsche 356 type vent ring.

Last. If that engine was set up as per factory with the right distributor and proper air cleaner you would see the thermostat work even more (be closed more and go to full open when you use the power.

Just to add to the gaining of info.

T

[volkaholic1]

so some more data on the tennis ball trick, I have made 13 runs, not a ton of data, but a good start, with outside air temps running 70-85F, the AVERAGE engine compartment air temp is 46C = 115F, the air the stat is seeing is 81C= 178F,Ihave 4 runs with the tennis ball, engine compartment air temp drops to 38C=100F and the air down at the stat is 69C= 156F. Interesting, at the lower air temps, the stat slowly closes to try to raise the engine temp.

So, with the stock setup, the engine compartment air is like 30F hotter than ambient. cracking the decklid open knocks the air temp down about 15F. I have bought 2 parts i will try out soon to see what effect they have.
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Volkaholic

[nextgen]

Volkaholic- I have seen you around, you just blew me away. Were were you when I was doing T-1 fanhousing on T-4 engines ????

At the time before the internet I thought I was the only guy working on T-4 Upright Conversions. Seeing it was totally new I went with the T-1 fanhousing and not take any chances, used the stock Flaps and T-1 thermostat frame, which I mounted the spot were the T-4 had the Thermostat cable pulley.

The car ran too cool, which I figured was great, but unaware it was not reaching running temp in temps below 70f. Ran like crap like any engine that did to warm up. Every Saturday I would go to the Post office get my PO Box mail and noticed after the 1 mile drive I turned the car off, then 5 min later, restart and the car ran smooth. Took like 10 trips to figure my thermostat was opening to fast. The 5 mins with the fan off let the engine heat evenly. It had a 80 c , thermostat and went to 90 c and my problems went away.

It being a cross between T-1 and T-4 was unique and had a lot of trials.

Checked carbs, Ignition, Timing, regular and super gas etc.

When all it was, was the thermostat.

That said, as simple as the thermostat may be, you showed us how really important it is.
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[volkaholic1]

and back at yah, thanks so much for the next gen book, i used it to build my 2 l type iv engine in my 68 bug. very helpful. i hate to admit it, but that engine does not have flaps,,, but it will, I am going to pull the engine, go from 94 dished to 96 flat top pistons, twin plug the heads, then put flaps on it. should be a world different engine after that.
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[nextgen]

It was a world of difference I had that combo in my 914 with a cam, crazy fast -- but only 1 plug per cylinder
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[Towel Rail]

Great stuff, @volkaholic1. We can glean a lot of wisdom from VW's design decisions over the years, but gathering good data lets us find out even more and advance the hobby.
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[nextgen]

The aircooled VW engine was made as simple and precise as possible.

The thermostat with is a perfect example.. the engine has very fine line that prevents overheating.
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[volkaholic1]

yes, these thermostats are a 100 year old design, back in the day, other cars used almost the same exact thing, i know the 1928 caddilac does, also, old rolls royce, bugatti, and an italian car all used them as well. The big difference is that all those cars are water cooled, but unlike a modern car that has a thermostat in the radiator hose the controls the water flow to the radiator, they had the stat sitting in water, and it went to a rod that controlled flaps behind the radiator, they controlled the air flow instead of the water, this was a much more complicated system than is used today, but is similar in concept to the bug flaps.
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Volkaholic

[nextgen]

I totally agree and remember the Thermostat with the flaps for doors on the thermostat then were in the Radiator Pipe.

Like you said that was easier to control. The first thing guys would do if there car was overheating would be remove the thermostat.

Like the air cooled version they would put it in hot water to see if it will open.

Most guys like some VW guys said, screw that part, who needs it if it fails my car overheats.

As you know my conversion is the only T-4 conversion that uses a Thermostat.
As you also know the T-4 runs extremely cool.
Guys in warm climates can get away with it but, to guys like me in NY, not knowing you are running cool, can drive you crazy looking for why your car is running like crap. .
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[volkaholic1]

latest update, i put duct tape over the decklid vents, to simulate an earlier deck lid, to see what the effect is.

not going to win any best of show awards, but this is only temporary, so i will let it slide.

I decided to focus only on 30+ miles drives, going 55-60 mph to get the best data. I looked at 4 runs with similar ambinent starting temps
two at 30C, two at 22C, comparing the starting temps with the highest air temp recorded down at the thermostat we see the following

run 13 tennis ball trick has the lowest temp
run 16 started at nearly the same temp as 13, but got 10 degrees hotter
run 15 is the stock setup
run 17 is higher starting temp, highest ending temp

What does this tell me? at lower ambient temps, the extra vents on the decklid don't really do a whole lot, but at higher temps they become important.

this chart is a little hard to read, i am trying to show 3 different things, all temps start at ambient 30C, stock setup vs taped vents. green = stock, red = taped, you can see that the stat temps are higher, while engine compartment temp and oi temp is surprisingly lower, not sure what to make of that.

lastly, best case vs worst case, comparing tennis ball trick vs taped vents. In this case, as you would expect, all temps are lower with the tennis ball trick than with the vents blocked off

i have some other parts i will try soon, but here is a question, i have never had this car over 60mph, i am starting to think some 70 mph data might help highlight differences, your thoughts?
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Volkaholic

[74 Thing]

70MPH is more realistic of highway driving. I'd be interested in seeing data with that speed using similar air temps.

[Lingwendil]

I agree, do it again at 70MPH or so, it would be a bit more telling. The overall trend looks good though.
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[volkaholic1]

i scored this vintage Herrod Helper at the VW show in Perrysbuge OH, $10, complete with original hardware and gaskets, it was RUSTY RUSTY RUSTY! - I blasted it down and powdercoated it gloss black, you can still see the pitting so not show quality, but perfect for my neede. If you don't know, this part came out in 1974, they claim improved aerodynamics and up to 2 mpg increase in fuel mileage, but the reason i got it is that a friend told me is also help get more air down into the vents - This is a testable hypothisis!

maybe others sell them, but i know aircooled.net does, they are aluminum now instead of steel.

results, showing engine compartment air temps, stock is the hottest, taped over deck lid vents is a close 2nd, the Herrod Helper is in the middle and the tennis ball wins for lowest air temp

So, that tells me it does make a improvement in air flow into the engine compartment.

Now, why is stock hotter than taped over vents? note they are pretty darn close, I think 2 things could dramatically change that, speed you are driving and outside temp. If I was driving across NM or AZ t 70 mph and it is 115F outside, those vents would make a much bigger impact.

anyone live someplace hot and what to try it out for us? I could build a little kit, you install it, publish your results here, i pay you a small commission for it! everyone wins!
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[ALB]

[Steve Arndt]

A pressure reading in the engine compartment vs temperature would be helpful.
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[veeweeman]

Maybe I'm being a dick...but to be honest, I've never run a t-stat on any stock or modified engine that I ever built and have never had a problem. ..all my builds or rebuilt engines were in central CA...I think and believe that thermostats don't belong in CA cars or not needed. ..just my opinion. ..I have torn down dozens of CA engines and I have never seen any thermostat system on a CA car...I believe that the thermostat is only needed on extreme climates.

Just my input from CA area.
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[KTPhil]

[Coyotemutt]

Really makes me wish I had a thermostat. I can tell you, from running a CHT sensor, that my engine definitely does NOT run at a steady state. And I live in New Mexico and have to pull alot of steep hills. Sure, on the freeway here it stays at about 350f to 380f depending on load. But get off the freeway? Just downshifting, even in hot weather, will drop the head temp to 300 before you get to the end of the offramp.

I ended up rigging a spring to hold the flaps full closed for warmups and short trips around my little town. Wish I could afford a reproduction thermostat right now.