ShopTalk Forums | Aircooled VW Tech & Restoration Help

Exactly....

Thats what I try to explain to everyone..

ACTUALLY YOU HAVE DECRESED LOAD!! The shorter tire has lowered your gearing!

Oil temps are a DIRECT relationship to RPM

No, you read it backwards. When I went to the taller tire it caused the rpm to drop, and instead of lower oil temps like you predicted above, the oil temps went up significantly.

okay, I was dyslexic for a second- sorry..

A taller tire will increase load, and decrease fan speed at the given MPH. That can heat up oil, but SHOULD heat up heads as well.

Bruce, are you running especially high ratios in your tranny ? - Like higher than factory ratios ?

24,5" is close to stock height tyres.
The only times I´ve seen reactions like that is when higher than stock ratios are being used, like f.i. 0,82 4th gears on 4,12 or 3,88 R/P (and stock type cooling) The reason is actually explained by, well, Berg. At normal driving, say 55 mph, the fan does not deliver enough cooling air when running at so relatively low speed. Same engine and setup run at say 70 mph, and you will see a decrease in both head and oil temps., because the fan now produces more air.
Very "square" explanation, I know.
A friend of mine actually runs a tranny w. 4,12 R/P and 0,82 4th. 24" tyres. if we measure oiltemps at 50 mph and at 70 mph the temps drop about 10 deg. C.
T.

Yes, but that Berg propaganda does not apply.
When I built the gearbox, I picked 3.88/.82 to counter the small diameter rear tires. My engine and fan speed were exactly the same as with stock tires and stock gears.
The reason the Berg bs doesn't apply is because I increased the fan speed via a 36hp lower pulley. I am currently just a hair under 2.0:1 pulley ratio. Even now, my fan turns at the same speed as stock at speed. But my engine rpms are lower than stock.

Something is weird with your combo... what shroud do you have?

Its a VW Industrial DH shroud. Same as a T181 shroud but without the holes for the cooling flaps. (that's right, a factory shroud without the cooling flaps or a thermostat) The slot for air to go to the cooler was only about 3" long, so I opened it up to the same as the regular car shroud. Then I welded in the scoop to direct more air into the cooler. That scoop is missing from the 74 Bug shrouds I have seen, present in 71-72 shrouds. Do you know what I'm refering to?

Shroud has been modified to take a T4 cooler. All unnecessary holes and gaps were welded up.

I then drilled the holes for the cooling flaps and installed the flaps, welded in the wide open position (since I have no thermostat; exh in the way) I bent the flaps a little more to direct more air over the heads (CB 044)

I also had a FI venturi ring, so I welded that on over the inlet of the shroud, after removing the factory screen.

I spent the time to sink the fan as deep as possible into the shroud to minimize cooling air spillover. This is one step that I've never heard of anyone doing. Mr. Bentley doesn't mention it.

The fan is a standard German fan, welded.

Bottom pulley is a late 36hp, sectioned and widened to take the 11.3mm alternator belt. The belt is standard length, and with the bigger bottom pulley, it rides really deep in the top one, achieving near 2.0:1 ratio.

That's me above.

Jake, did you test any shrouds with the venturi ring? I have now been thinking about welding one onto a 36 Shroud... How did the water mister into the fan work out? Thanks.

Yes, I did a venturi ring test.. It helped by about 10 degrees across the engine, but did not help with the higher drive ratios- stayed the same.

I have seen factory shrouds without flaps and T- stat provisions. Brents Ghia had it from the factory.... Necver seen it before, his is a 40 Horse... we looked for 5 years to find all the correct tin for that engine.

Bruce.
You seem to have taken every percausion that could be thought of. And with the extra ratio on the fan belt their should´nt (at least in theory) not be a difference.
However. I, and others have spotted this same fenomenon, when using T4 coolers w. T1 fanhousings.
When the fan revs at normal ratio at normal speeds in a bug with closed lid etc. the oil temperature seems to stay higher (5 - 10degr. C.) as if it was mounted w. the regular T1 cooler. It sort of equals out the more fan speed that comes on.
But in a bay bus f.i. w. a 1600 tranny, where the engine revs significantly higher than in a beetle, there is a small gain in upper midrange oil temps. lower speeds and full load is about the same as stock T1
When we found out how small gains there was by this "improovement" we stopped making them.
i do not know if that is your problem, but it sure sounds familiar.
Torben

Jake, do you know about the scoop by the oil cooler slot I refered to above? Did you test shrouds with and without this scoop?

Yes, I did test the shrouds with each type of scoop... wait for the results in Ultra VW..... There was a difference, especially on the #1 cylinder..

Alot of your precautions are working against each other......

When can we expect to see the article in Ultra VW's?

MASSIVE TYPE IV wrote: Alot of your precautions are working against each other......

The only thing I can think of is the cooling flaps since your tests last week says they increase temps slightly.
What else?