airflow through boot lid

Can anyone tell me which way the air flows through the bootlid on a watercooled speedster. I am thinking about installing the oil cooler below the grill cover. Will this create problems with the oil draining out the cooler on shutdown? Should I suck the air into the engine compartment or blow out?

Glad that someone brought up this topic,,, as I was about to ask pretty much the same question. My application is a bit different,, ie: aircooled 1600cc's, but what concerns me is also where to best position the oil cooler. If the engine compartment is well sealed with proper engine tins, then I would expect that air would normally flow in from the hood grill. At speed,, the air stream should be coming down onto the rear hood surface,, and the engine fan should be drawing air from the sealed off upper engine compartment via the grill. Has anyone ever taped a "wooly" (yarn) to the grill, and then noted where it is drawn at different speeds ??

But assuming the airflow is in through the grill, I am not sure that having the oil cooler transfering heat into the upper compartment, and then subsequently through the engine is the best arrangement.

I was considering cutting a hole in my tin, and then mounting the cooler to the tin. A thermostatic switch would turn on the pusher fan to send the oil coolers heat out the bottom of the car, and away from the engine. The fan would also draw air in the grill, as well as any other installed ducts or or leaks. Obviously,, it is critical to have some form of reliable guaging in place, to know what is happening to your engine cylinders and heads.
Opinions,, Please
Alan

Count me in as well. I would also LOVE to know if the air flows in from the front as it goes over the car, or is it sucked in through the back end because of a low pressure area created by the blunt rear of the body styling?

If the deck lid were propped up in the front would it act like a scoop? I see that some cars have holes behind the number plate, is this to let air escape or allow cool air to enter?

Really curious about this!

I think most of the air enters from under car, above the trans. If you look in the CMC/FF build manual you'll see they have you cut out a 3/4 moon section of fiberglass firewall there. See

https://www.speedsterowners.com/library/cmcmanual2/images/cmc43.jpg

So air would flow in there and out the engine grill when moving down the road. I believe the oil cooler should NOT be mounted higher than it would normall sit on an engine (due to oil running back into engine case on shutoff). Additionally I don't think it should be too far from the engine --- long lines say to front of car reduce the oil press and decrease the flow.

Best oil cooler location is mounted horizontal above the left axle area, it gets clean cooler air there, it's an easy install with a few hand fabricated brackets.

A few years back I had a Manx with an oil cooler mounted high on the fender, my son had a Baja, again it had an external oil cooler mounted out side on the fender, so being high didnt caused a problem, there seem to be 101 oil coolers avalible in the US to choose from, both with and without a booster fan, heres a link for those interested

http://www.thesamba.com/vw/forum/viewtopic.php?t=117932

I will have the same issues as Greg, using a Subaru motor, naturally being water cooled we have ( I hope ) good temp control, Greg is using a water cooled tubo intercooler, I'm going to use the std air cooled intercooler, to boost the flow of air over it I have mounted an electric fan in the engine cover lid, if i have it running the wrong way, ( plan to suck the air in from the out side ) will be simple to revers the fan direction , sure the down side is the air after passing thought the intercooler will be heated and flow onto the motor, but thats how Subaru do it and they have a pretty good R&D budget so i figure it cant be all bad

I'm also interested in other peoples opinion on this

Time and miles on the road will tell all in the long run....

Regards From down Under Bill

Actually the fresh air enters from the top of the grill and from the cut out in the firewall. The hole behind the license plate is also a fresh air inlet. In all these air cooled cars all the hot air is expelled from the bottom of the engine on to the back of the car; that's why you need to totally isolate the bottom of the engine from the fan housing area via the tins and seals. You don't want hot air expelled from the engine to be re-circulated back to the fan housing; you only want fresh air in there to keep your engine alive. The best place to put both your oil filter and cooler is definitely out of the path of hot expelled air.

Richard, you didn't mention the air that enters from around the entire edge of the rear engine cover - the reason for having those little rubber bumpers instead of the more intuitive full weather stripping. My firewall to the tranny area is solid, with no cooling holes at all.

I've got a large remote oil cooler mounted high inside the left rear wheel opening, with a thermostatically controlled fan that blows air from the tranny are out into the wheel well area. Absolutely no issues with the height. The remote oil filter is also mounted in the same wheel well, and it is also well above above the sump.

Dave; I installed the 356 rubber thingies under my decklid because I read that too but I haven't noticed that much difference in the cooling. I also built and installed an aluminum scoop to blow fresh air from under the car as per Gene Berg's technical articles but I don't seem to see that much difference in the cooling either. After driving for 15 or 20 minutes over 65 mph my Gene Berg oil temperature dipstick gets the oil light flickering (a sign that the oil temperature is getting high). All that and my motor only has 7.1:1 compression.

Ricardo - You must have something else going on that's causing your heat problems. I have no air scoop, but I do have an external oil cooler, and I can drive for quite a while in all kinds of traffic and stay below 180 as long as the ambient temp is in the 70's. If it's hotter and I drive at sustained freeway speeds, I will get up to 190. I have a 1915cc and I think my compression is around 8:1. I have one of those Mainely Custom dipstick thermometers, and I like being able to get a pretty accurate temp reading. The peace of mind is worth the $50.

Hey Bill Smith. I don't know what part of the country you live in, but after looking at your pictures posted above, I got this visual image: It's a bunch of speedster guys sitting around on the back porch at night, downing a few cool ones and somebody says how dang hot it is. Bill goes over and pops the deck lid off his car, sits down with the deck lid on his lap and clips the wires onto a 12 volt. Fan starts "cooling" and Bill is chillin' out.

From what I've read you shouldn't need an extra oil cooler if the engine is configured correctly; plus it takes away the extra plumbing which adds possible leaking points, etc. A full flow oil filter should be more than enough and do the trick. I still don't know why it's doing that unless the Gene Berg dipstick is overly sensitive and it's already flickering at an acceptable (albeit high in the range) temperature. Carbs are nice Dellortos, jetting is correct; exhaust system is less restrictive; compression ratio is low, have an SVDA distributor, OEM engine tins with all of therm in place (such as the famous "Hoover bit" under the oil cooler) has nice big valve heads, has the scoop contraption, the snubbers under the grill; nice heavy oil as recommended by the factory for tropical temperatures; I'm stumped. Remember also the temps in Puerto Rico are 80's and over.

Hi Recardo. I take your point regarding the extra potential leaks. I still feel that the motor is running a few degrees hotter than I would like. The guage stabilises at about 95 degrees Centigrade. I would prefer to bring the water temperature down to about 85-90 degrees centigrade. During summer it is quite common for the temperature to be between 30-35 degrees Centigrade.

I also like the extra oil capacity thet comes from the remote oil cooler.

I will be mounting the oilcooler next to the gearbox.

Hi David
I

What Bill said . . .URRPPP!

Whether or not you need an external oil cooler may depend on how you drive and where you live. In southern California it can get 110 degrees (a weather condition called Santa Anna). Couple that with average freeway speeds of 75 to 80 MPH anytime of day. Go any distance under those two conditions and air cooled engines can start to heat up pretty fast. On the other hand, I can putter around at 60 MPH or in city traffic all day long and the oil temp gauge barely comes off the peg.

My cylinder head temp gauge keeps me honest, and confirms what I just described.

David,,
What type of cylinder head temp guage do you have ??
thanks,
Alan