I was debating where to put this thread, but it's baja specific, so I figured I'd put it here.
As an introduction, we who run air cooled engines always seem to be debating and discussing oil coolers, oil temperatures, oil viscosities, air flow, head temps, etc. As someone who clearly doesn't have all the answers, I've tried various things to keep my temperatures in various motor combinations within a reasonable zone. With somewhere around 20 years at this, and 17 years with my current sled, I finally made something that works...
And it works WELL.
Most will agree that oil temps are to be kept under 230 if all possible. Some of mine have run hotter than this, especially on hot days, and/or pulling long hills. The accepted "BEST SET UP" to keep modified engines running coolest is to have an original German fan shroud, with its fins intact, and a doghouse cooler and fan, along with original German head tin. The VW Thing fan shroud is really well suited for a baja bug, as it doesn't have the tubing extensions for the fresh air heater hoses to hook to, which most of us threw away and welded up the holes in our pans many moons ago. It's still not as cool looking as the 36 hp style shroud, so there is always a trade off.
I have a Thing shroud, and all of the stuff to convert it over to the system mentioned above, but due to an unfortunate turn of events the other day, my plans had to be modified. My oil cooler sprung a leak on the trail and spewed engine oil all over the place. Since we had a club run planned for this Saturday, I had to fix it quick and get it back running again. That's where I'm starting at with this post. Here's a picture of what I started with:
I have one of those aftermarket coolers plumbed into the original oil cooler location, with the original cooler removed. I also have a doghouse style fan (wider), but a non-doghouse aftermarket fan shroud. The fan is thermstatically operated. On a reasonably warm day, it runs about 220 on the freeway, and if really hot (100+) or pulling a hill, it runs 230 or even hotter. It's run this way for years, with the 1600, the 1641, the 1835, and even my current 2187. I've run all chrome aftermarket tins and shroud, and I've run black, and now I'm running the real to match the body. I've noticed no difference in temperature. I've painted the engine black, the cylinders black, and even the heads black. No temp difference. I've run tube type coolers and plate type coolers. No difference. I've even experimented with running the cooling fan in reverse (sucking from the bottom) and noticed no difference.
I finally made a modification that made a difference. And it was a HUGE one.
For whatever reason, I'm one of those guys that cant just run down to the store, buy a part, and bolt it on. I just seem to always find improvements that can be made to products that are mass-produced to make money for large companies, rather than provide high quality upgrades. I thought I was just going to buy a cooler and bolt it on, but it didn't work that way. I found a cooler that I liked, a 96 plate cooler, from Mooreparts. I brought it home and bolted it in. I looked at it when it was done, and saw improvements that could be made.
I'm sorry I'm going on and on, but I'm really happy with the results of this experiment. Bear with me.
The biggest problem I saw, was that only about 50% of the cooler is really used when you bolt a fan directly to it. The fan doesn't reach the corners or even the outside of the cooler itself. There is also no airflow at all in the middle where the blades meet the hub of the fan. I knew I needed to build a housing to ensure equal air flow through the whole cooler.
If you think about oil flow for a minute, you know that as oil gets hotter, it gets thinner. When the hotter, thinner oil is not getting adequately cooled, and the part exposed to the fan is, you would think that the hot oil actually passes through the cooler faster than the oil getting cooled. Therefore, the cooler oil is really not getting to the engine with any regularity. I don't have the real figures, but think about this: If only 50% of the cooler is cooling properly, and the hotter oil is passing through the cooler 50% faster, your cooler is only operating at 25% efficiency. We need a better design.
I made a shroud with some steel framing, angle, and sheet metal that I had laying around the garage. It's not production quality, as it's only really a prototype to see if I could help with the efficiency. The design principle is as follows: I made sure that there was a 2" gap between the fan and the cooler itself to promote even flow to all components. I made sure to add foam to the edges where the cooler met the steel framing to prevent precious air from escaping. I made sure that I got cool air in, and directed it out and away from the intake for the fan shroud.
Here's some pictures:
Here's a picture of the way the mounting bracket looks that bolts to the car.
This is the air deflector that directs the hot air out. It just slips in with slots that hold it sandwiched between the bracket and the cooler mount.
This is the top side of the cooler shroud that the fan bolts to.
Here's the fan bolted in (no air leakage).
Here's where the cooler bolts on from the bottom side. It has very little air leakage where the cooler is bolted to the frame. Also there is foam along the sides to prevent the air from escaping.
Here's the whole thing bolted in. I had to grind the corners out of it to clear my fiberglass cowling. I'll need to make improvements in the "curb appeal" of this part of it in the future.
OK. Now for the results: I drove it to work today on the freeway (30 miles) and the temp got up to a hair over 180. Normally this time of day it would run at 210. I haven't seen it at 180 on this section of road, even in February! I drove it home and it actually got to around 195, maybe even to just under 200 when on the Tujunga hill. It was only in the low 90's at that time, but usually I would expect numbers around 220-ish on this type of day if I was taking it easy, and I wasn't today.
That's a HUGE improvement... I would say 25 degrees as a conservative average. Of course, this is only one day of data, but is a noticeable improvement for sure.
I hope that this post helps someone out there. It was great news to me.