cruising, fan speed and cooling

[Rocket Ron]

I am considering another longish trip with my beetle this summer and was wondering if you had any thoughts on the optimum rpm and fan speed to provide cooling on longish motorway trips. I've alsway struggled to find the best cruising speed to cool the motor on extended higher speed runs.

Car has doghouse oil filler, external oil cooler, smaller style deep sump, standard generator and stock sized bottom pulley and good fitting tin with seals. Compression is 9-1 ish and 2276 with stock casting heads.

Trans is 3.88 and .89 with 205 70 15 rears

Welcome your input

[modnrod]

I've never really driven much in your temps, but if it makes you feel any better 3000rpm @ 68mph (a guess at your revs and speed?) for my winters are OK at about 20*C with most engines, but in hotter spring/summer days it would start to get marginal at temps over 30*C here with a normal-spec tuned engine. For my Superbug, with a 311-headed 1800 and all the tuning/airflow/cooling/oil tricks I can muster, I'm still not daring to go past 65mph @ 3000rpm at light cruise, but I have to deal with 45+*C and under 10%, and even then I rekn it will be touch and go to be honest.

Your conditions are completely different to mine of course. Perhaps consider tinkering with the amount of shims to change the fan ratio while on your trip? Fit a venturi ring for an extra 5% airflow by most counts? Take the edge of the engine tune to get better cooling at highway cruise? I think 3500rpm gives the best airflow, but if you need to sit on 80mph to get it then it might be cancelled out by the extra aero load of the speed.

I've always found myself coming back to the tests run by these blokes, puts it plain and simple........
http://www.offroadvw.net/tech/wes/fan.html

[Donny B.]

Here in Phoenix we deal with high temperature all summer long.  110-120 F.  I am running stock final drive in my car 3.12 R/P .89 5th gear.  I found very early on the I could cruise at 3200 rpm about 60mph and the oil temp would drop 10-15 degrees when I upped my speed to 3600 rpm.  I have found that my engine is happiest cruising between 3600 and 3800 rpm.  I usually cruise at 75 mph for long distances (100 + miles).  I am running a doghouse shroud with a type IV oil cooler and a remote cooler with a fan.  I also have an oil thermostat between my filter and the remote cooler.  Oil only goes to the remote cooler when oil temps get around 175-180.  I have people tell me I was stupid for running those rpms for long distance, but it works for me.

[richie]

Trans is 3.88 and .89 with 205 70 15 rears

Welcome your input

That is to tall, 70mph is only 3100rpm, for me the fan is not spinning quick enough, 60mph is about 2650rpm, way to slow, bigger 912 top pulley to speed fan up would help

[Martin S.]

There are two aspects to bug engine cooling. Heads and oil/case/bearings. It helps to identify where the problem is and go from there with a solution. If you can check the heads for temp that could help decide if you need more fan speed for the heads, or if you need more oil cooling for the case. For example on my turbo, the heads are fine but the oil is being heated by the under the decklid turbo. At least that's the theory. I have the same problem where going over 100km means the oil temp shoots up but the heads stay cool. I still don't know if gearing would work better than more oil cooler, or if I need a combination of the two solutions. I wish I had some big diameter tires to test out the taller gearing theory.

[Jim Ratto]

I tend to hover around 3800-4000 on freeways around here, if I can.
I think another factor to think about is "where is the engine happy?", meaning, where is vacuum signal strong and is your fuel curve giving the motor what it needs in air and fuel, lb per hr so it's a happy air cooled motor? If you run an FK89, bobbling along and burping at 2750rpm isn't giving thed motor what it wants. It may (probably) run cool, depending on jetting but if may be difficult to jet correctly in that rpm range, causing the motor to hiccup on too lean a mixture, until it comes on cam, and sends the message loud and clear to carb circuits. Choosing the right emulsion tube for your motor here is crucial. Just something to be aware of, aside from pulley and final drive ratios.

[nicolas]

this may also be of interest as i had a big difference in cooling and temperature because of the air that was provided to the carbs. it may not relate to you, but this is what i experienced.
the engine was similar to your 2276, but in a type3. so no seals in the engine compartment that would effectively close off the hot air from the exhaust to the carbs. that was a big problem on the car. if i popped open the deckled there was circulation and the hot air could get out better and fresh air was drawn in better. this was a big improvement on the overall oil temperature and mostly seen when the car was stuck in traffic jams as it would get even hotter then.
it's just an extra thought, something that drove my temperature up.
i also had a 4.12 standard geared type3 box and that is what suited my needs best and like stated above RPMs would be a higher. i think it is a good all-round gearing if such a thing exists.

[Rocket Ron]

Thank you all for your valued input

Reading through your posts it tends to climbing head temps that I suffer from on longer runs so maybe a few more rpm would be good tend to stay around 3100 - 3300 rpm on a run maybe a 65 section tyre would help here.

I will be relocating the external oil cooler into the air flow a little more also. The biggest mistake I think I made was to run a aluminium case but  hey live and learn.

Out of interest what oil and head temps would you consider comfortable or hot

Regards Ron

[Neil Davies]

So Ron, you need to print out this thread and when you get pulled over for speeding, you can just explain to the nice policeman that you were keeping fan speed up and engine temps down! It's bound to work!

[richie]

Little more info that maybe helpful, stock 1303s which seems to have the tallest overall 4th gear package shows 70mph as 3300rpm so you are not to far off, but you would need to go to a 205/60/15 rear tyre to get close to that

I like oil temp between 195-210 when cruising on motorway, but the gauges don't all read the same so its difficult to be 100% specific

cheers Richie

[Rocket Ron]

Little more info that maybe helpful, stock 1303s which seems to have the tallest overall 4th gear package shows 70mph as 3300rpm so you are not to far off, but you would need to go to a 205/60/15 rear tyre to get close to that

I like oil temp between 195-210 when cruising on motorway, but the gauges don't all read the same so its difficult to be 100% specific

cheers Richie

Didn't see your earlier post

Think Jim Ratto was selling a couple of 912 top pulleys I'll pm him and it's time for some new rears tyres anyway 

[RIP356]

Just on cooling
Has there been any testing between stand offs and opening the bottow of the engine lid?
Building my car now and dont know which way to go, i couldnt find a vented engine lid?
Dave

[Zach Gomulka]

I stood the lid off at the bottom and the temps immediately went up. Pulled over, closed the lid properly, and the temps went back down. I did have a factory 4 vent lid, I assume a solid lid would give a different result.

[Jim Ratto]

Little more info that maybe helpful, stock 1303s which seems to have the tallest overall 4th gear package shows 70mph as 3300rpm so you are not to far off, but you would need to go to a 205/60/15 rear tyre to get close to that

I like oil temp between 195-210 when cruising on motorway, but the gauges don't all read the same so its difficult to be 100% specific

cheers Richie

Didn't see your earlier post

Think Jim Ratto was selling a couple of 912 top pulleys I'll pm him and it's time for some new rears tyres anyway 

Hey Ron got your pm, yes we sell OEM 912 pulleys, I'll pm you information. The pulley will help, but only so much, the rest of the recipe needs to be "right on" too.

[WhiteTrash]

bigger 912 top pulley to speed fan up would help

I thought the 912 pulleys are smaller? The same as 356's. As you'd use them with the power pulleys to get the fan speed up to original spec?

Frank

[richie]

I knew what I meant   and my theory is correct, they speed the fan up at lower rpm than stock pulley

[WhiteTrash]