TheSamba.com :: View topic - True or false. cracking the engine lid cools better?

Fri Jun 29, 2012 12:45 pm

I always thought it was a bad ldea to have it open on the hiway But ive seen alot of people cracking them open or not running thier lid at all. Does it make much difference either way?

Im taking the first road trip with my new motor in my bus this afternoon and its a 1915cc and I havent mounted my external cooler/fan setup yet and its over 100 degrees here. so anything i can do to help keep it cool i want to to do before i hit the road.

My engine compartment seals are new

so pop it on the hiway or keep it sealed??

Fri Jun 29, 2012 12:52 pm

Sealed. It creates + pressure. Any leaks just lessens the cool air flow.

Fri Jun 29, 2012 1:16 pm

Seems like you need to get extra positive pressure in the engine compartment ASAP if you've got that motor in there. That's what the side scoops on baywindow T2's was for, and a split doesn't have that.

Fri Jun 29, 2012 1:48 pm

I propped my lid open on my Oct 62 and got 30* drop in head temp and 50* oil temp on 108* day going up the grapevine in CA.

Fri Jun 29, 2012 3:07 pm

If the engine is new, think about not driving the bus at a steady speed until the engine is broken in. You want to give it gas, which causes the rings to expand against the cylinder wall, helping seat them, then let off on the throttle, which gets oil onto the cylinder. Driving around a town is a good way to do it.
Regarding leaving the engine door open, hot air is blown out from the rear of the engine (cylinder heads and cylinders) and some of it would go into the engine compartment.

Fri Jun 29, 2012 3:19 pm

type241 wrote: Sealed. It creates + pressure. Any leaks just lessens the cool air flow.

Your logic does not compute. If your assumption is correct there should be positive air pressure in the engine compartment even at rest. Clearly this cannot be the case. The only way that "cool air flow" into the compartment can be accomplished is by the fan displacing air out of the compartment which is sealed to prevent reentrance of previously-cool-and-now-hot-air into the compartment. Ideally, the engine fan sucks only ambient temperature air which is replenished as the fan blows it over various parts of the engine. That is why VW located the vents on the side of the bus and not the decklid. Because there is a dead zone of air flow behind a bus, especially at speed, the possibility of recycling engine cooling air is very real. (For evidence of this dead zone one need look no farther than the oil mist which coats the backsides of many buses.) I know from personal experience that opening the decklid can help cool an engine which runs hot when it is warmer than usual. However, this runs counter to my theory of the dead zone.
Usually, the problem is the cooling demand of the engine is increased as the HP is raised. This requires additional air to flow over the engine. That is why VW increased the number of vent louvers as well as the size of the fan. Often the size of the air intake on the body is the limiting factor which cannot be easily countered by the fans speed or capacity.
Make sure every avenue of possible entry for hot air from under your bus has been closed off. Then run it with the decklid closed and then open to see how much of a difference it makes.
I used to have SC which had a little trap door on the shelf in front of the engine. The PO cut it in to access the upper engine bolts, initially. Then he but in a magnet on the firewall to hold it open when it was hot outside. It worked very well. I've considered installing them on other trucks I've had, but just couldn't make myself hack them up that way!

Fri Jun 29, 2012 3:58 pm

In regards to "dead zone" of air behind any moving vehicle, that does not exist. The air is lower pressure but quite turbulent. If you need evidence of this, look for oil spots on the rear decklid and hatch if your engine is dripping a bit of oil at speed.

Fri Jun 29, 2012 4:50 pm

The cross section of the engine vent openings on a bus is much greater than on a beetle. Since the beetle has basically the same engine, even if the bus needs more air to cool since its pushing more weight around, then there is plenty of air coming in the engine vents for proper cooling.

If your engine is overheating, fix the problems causing that, giving more air to the engine compartment is just a band-aid.

Fri Jun 29, 2012 6:32 pm

j.pickens wrote: If your engine is overheating, fix the problems causing that, giving more air to the engine compartment is just a band-aid.

Jay-Dot is right on the $$$ here! ^^ Trial by 'fire'?

Fri Jun 29, 2012 11:55 pm

I am having one of those deja vu moments....any minute we are about to get a dissertation from Jake Raby on pressure and flow , and how the tests are not equal.
All I want to add is... seals are there to seal, they were put there for a reason.

Gordo.

Sat Jun 30, 2012 5:08 am

Busryder wrote: j.pickens wrote: If your engine is overheating, fix the problems causing that, giving more air to the engine compartment is just a band-aid.

Jay-Dot is right on the $$$ here! ^^ Trial by 'fire'?

X3! Built correctly, a huge displacement engine will run cool in any bus. BTDT! I run a 2276 in my Dormy. All day long @ 70-75mph runs 250*F on the head and 175*F on the oil. When pushed hard the oil may get to around 210 or so but will drop back down as soon as I let off it. 8)

On an aluminun case, no less!!! :P

Sat Jun 30, 2012 7:18 am

Looking at this debate, I see a bunch of opinions and guesses, and one person who measured the difference. Has anyone else done those back-to-back tests along the same stretch of highway, with the engine lid open and closed? Right now the evidence from the Altewagen seems pretty good.

Sat Jun 30, 2012 8:06 am

Don66bus wrote: Looking at this debate, I see a bunch of opinions and guesses, and one person who measured the difference. Has anyone else done those back-to-back tests along the same stretch of highway, with the engine lid open and closed? Right now the evidence from the Altewagen seems pretty good.

My experience is not a guess or just opinion and my measurements are done with calibrated instrumentation. :?

Sat Jun 30, 2012 8:24 am

pyrOman wrote: Don66bus wrote: Looking at this debate, I see a bunch of opinions and guesses, and one person who measured the difference. Has anyone else done those back-to-back tests along the same stretch of highway, with the engine lid open and closed? Right now the evidence from the Altewagen seems pretty good.

My experience is not a guess or just opinion and my measurements are done with calibrated instrumentation. :?

I think what he was saying was that most people's posts are opinion based, additionally your base measurement/data was posted but there is no comparison data to open lid (not that you would want or need to test that with your temps.)

Sat Jun 30, 2012 8:28 am

I did both a side scoop and open engine deck lid down here in Tucson AZ. I had an oil temp and head temp gauge. Initially my oil temp sender was on the plate for the oil dip stick location for type 3 blocks and my oil temps were very high and inconsistant at different speeds, but head temps remained consistant. Relocated the oil temp sender to a 'T' by the oil pressure port below the distributor gave me better oil temps.

Once that was set, my head temps were higher with the deck lid open by about 8-10 degrees. I had already 86'ed the scoops by this test so I can't vouch for any difference there. I ran the same ten mile run down I-10 at the same speed. Watched and recorded the temps at each mile post both directions. The segment of highway was between Tucson and Benson, AZ and has some steep up hills and down hill sections.

The only time my head temps were even with the deck lid open was when going down hill with little or no engine load.

I say keep the damn thing closed. That's the way VW engineers designed it.

Many will point out that Bay window buses have scoops. Yes they do and look at the location, they are high above the belt line where laminar flow is different and can be affected by an open window. The splitties vents were low, below the belt line where laminar flow is consistant and strong you don't need scoops.

Sat Jun 30, 2012 9:30 am

Don66bus wrote: Looking at this debate, I see a bunch of opinions and guesses, and one person who measured the difference. Has anyone else done those back-to-back tests along the same stretch of highway, with the engine lid open and closed? Right now the evidence from the Altewagen seems pretty good.

I did over 3,450 miles. Look at the Pilot's notes on each of these data logs to see I the decklid was propped or not and look at the CHT pan OT values for each leg o my run.
Www.aircooledtechnology.com/crosscountry

Race Technology 28 channel data logger power by SPA instrumentation.

Sat Jun 30, 2012 9:46 am

Great info Jake. But I couldn't determine where deck lid was opened or closed. Since that is the debate here. :D Numbers looked pretty consistant across the states.

Sat Jun 30, 2012 10:09 am

Jake Raby wrote: Don66bus wrote: Looking at this debate, I see a bunch of opinions and guesses, and one person who measured the difference. Has anyone else done those back-to-back tests along the same stretch of highway, with the engine lid open and closed? Right now the evidence from the Altewagen seems pretty good.

I did over 3,450 miles. Look at the Pilot's notes on each of these data logs to see I the decklid was propped or not and look at the CHT pan OT values for each leg o my run.
Www.aircooledtechnology.com/crosscountry

Race Technology 28 channel data logger power by SPA instrumentation.

This is informative but that was not a Bus, right?

Sat Jun 30, 2012 10:11 am

No, this was not in a Bus.. The same debate often occurs with beetles. I made 50+ cooling system changes on that trip and woul often test them with open and closed decks to see the effects each way.

Sat Jun 30, 2012 10:22 am

plane_ben wrote: The splitties vents were low, below the belt line where laminar flow is consistant and strong you don't need scoops.

It is difficult to change the direction of air in laminar flow. It either needs to be physically redirected (i.e. scoops in this case) or by pressure differential. Since it is so difficult it is possible that the laminar air rushing by on the outside of the vents could draw out air from the engine compartment by a venturi effect. The leaks in the sealing tins, etc. will be accentuated in this case, drawing in hot air instead of cool air.

As far as the dead zone is concerned, I did not mean that the air in it was still. The air flowing over, under and around a bus at speed will trap a low pressure "bubble" of "dirty" air which just stays in the aerodynamic shadow of the vehicle.

As the displacement of the VW engines increased in buses, the fan size (thickness) and vent area both increased. At the end of production the displacement of bug engines and the area of the vents were approximately equal to what they were in the late 60's. Buses, however, increased the vent area as the displacement increased. The reason that the scoops are high on the later buses is primarily due to the the cleaner air being up high. Just look at all the contraptions VW tried in various areas of the globe to pick up clean air. Trucks had the absolute worst location for the stock vents. AND they had one less vent on top of it.