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Thu Jul 18, 2019 9:39 am

Has anyone done a study of engine compartment temps?

It would be interesting to know how compartment temp relate to various scenarios .

100 deg day w/ lid closed vs cracked?
100 deg day with engine area sealed well vs. not sealed ? How fast does it warm up at a traffic light?
For convertibles ... top up vs. down?
2 rows of slots vs. 4 rows vs. no rows

How do compartment temps relate to head temps?

S

Thu Jul 18, 2019 10:33 am

Murmsk wrote: Has anyone done a study of engine compartment temps?

For convertibles ... top up vs. down?

I have an oil temperature gauge on my 1971 Convertible, 1835cc engine. Top up runs cooler than top down, measured same day.

I also have lid standoffs, and believe that they help similar to lid propped open.

Thu Jul 18, 2019 11:03 am

Two facts:

The first, as our engines grew in size, the VW engineers felt it necessary to provide more air into the engine compartment, via deck-lid louvers. I can safely assume that more available air meant more cooling air. Also, the size of the fan was increased to push more air, so more available air was necessary, via the increased number of louvers in the deck lid.

The second, I’ve read numerous posts where well-tuned (or even not so well-tuned) VW engines ran cooler when a louvered deck lid was installed, or stand-offs, or even a tennis ball. Oil and head temperatures were obviously lowered.

And it doesn’t take an engineer to agree that warmed-up air, coming from the flow of the fan and channeled by the tins over the heads should not be reintroduced into the engine compartment. An intact engine to body seal keeps most of this pre-heated air away from the incoming cooler air, as well as the spark plug seals, and various other means to preclude hot exhaust and head-channeled air from entering the engine compartment.

Tests have been done by those switching to louvered deck lids, stand-offs, tennis balls, etc. VW engines simply run cooler when these items are installed.

The cooler it runs—assuming proper engine running temps have been reached—the longer the engine will last. An intact engine thermostat/flaps system, regulates the engine temperature as quickly and thoroughly as possible, too. Combine with this, all tins and seals and you’ll be running the temps your VW engine was designed to run.

Tim

Thu Jul 18, 2019 11:05 am

Yep.

volkholic has done and is continuing to log legit scientific data regarding air temps vs engine temps in various conditions:

https://www.thesamba.com/vw/forum/viewtopic.php?t=705328

Thu Jul 18, 2019 11:11 am

Murmsk wrote: 100 deg day w/ lid closed vs cracked?
Think that air temperature in engine compartment wouldn't be much different either way. The main difference would be the air flow rate (i.e. amount of air that can get into and pass through the engine bay).

Murmsk wrote: 2 rows of slots vs. 4 rows vs. no rows
Same answer as above, the number of slots should mainly affect how much air can get into & through the engine bay, not so much what its temperature is.

Murmsk wrote: 100 deg day with engine area sealed well vs. not sealed ?
A poorly or non-sealed engine area would increase the temperature of the air in there, since the warmer air from below would be getting sucked back up into the engine bay around the sub-par or missing seals.

Of course, these are just my own personal SWAG's -- actual temperature data would be more definitive... :-)

Thu Jul 18, 2019 11:32 am

baldessariclan wrote: Murmsk wrote: 100 deg day w/ lid closed vs cracked?
Think that air temperature in engine compartment wouldn't be much different either way. The main difference would be the air flow rate (i.e. amount of air that can get into and pass through the engine bay).

Murmsk wrote: 2 rows of slots vs. 4 rows vs. no rows
Same answer as above, the number of slots should mainly affect how much air can get into & through the engine bay, not so much what its temperature is.

Murmsk wrote: 100 deg day with engine area sealed well vs. not sealed ?
A poorly or non-sealed engine area would increase the temperature of the air in there, since the warmer air from below would be getting sucked back up into the engine bay around the sub-par or missing seals.

Of course, these are just my own personal SWAG's -- actual temperature data would be more definitive... :-)

Check out the thread I linked above. I've been loving seeing the actual data on vented vs solid decklid, tennis ball trick, etc. Here's a taste of the gorgeous data sets

Volkholic is putting in a great effort in boosting our understanding of how these air-cooled engines behave and react in the real world :D :D

Thu Jul 18, 2019 11:51 am

the later big fan found in doghouse requires use of a louvered lid or stand off lid. at high engine speed and load, the fan competes enough with the carb to choke the engine under these conditions, resulting in power loss when using a stock non louvered lid. a stand off of about an inch at lid bottom eliminated the power loss.
I have run this test, it is very repeatable.

Bug On!

Thu Jul 18, 2019 1:23 pm

That’s interesting and what I expected. Points out the importance of following a few simple rules to have a cool running engine.

S

Fri Jul 19, 2019 8:23 am

AlmostHeavenWV_VW wrote: Check out the thread I linked above. I've been loving seeing the actual data on vented vs solid decklid, tennis ball trick, etc. Here's a taste of the gorgeous data sets

Volkholic is putting in a great effort in boosting our understanding of how these air-cooled engines behave and react in the real world :D :D
Ha! Yes, actual hard data completely trumps opinion BS every time (i.e. mine, in this case). :-) That is a very interesting read -- good stuff!!

Fri Jul 19, 2019 9:00 am

Although I will admit those high end temps he shows do seem a bit odd to me -- significantly higher than what the oil temp should normally be running. So how is air that hot capable of cooling the engine to begin with?? You can't get the engine any cooler than what the starting air temperature is (i.e. temp of air coming into the fan). Hmmm... What am I missing here?

Fri Jul 19, 2019 9:02 am

Wow 30 difference.

S

Fri Jul 19, 2019 10:01 am

baldessariclan wrote: Although I will admit those high end temps he shows do seem a bit odd to me -- significantly higher than what the oil temp should normally be running. So how is air that hot capable of cooling the engine to begin with?? You can't get the engine any cooler than what the starting air temperature is (i.e. temp of air coming into the fan). Hmmm... What am I missing here?

?not seeing what you mean? Make sure you're looking at 'compartment air temp' not 'stat air temp'

stat air temp = air temp at the thermostat under the engine (after it has removed heat from engine)

Fri Jul 19, 2019 10:22 am

AlmostHeavenWV_VW wrote: ?not seeing what you mean? Make sure you're looking at 'compartment air temp' not 'stat air temp'

stat air temp = air temp at the thermostat under the engine (after it has removed heat from engine)
You nailed it! -- I was misinterpreting the thermostat temperatures as the engine compartment temperatures. Makes better sense now, thank you! :-)

Fri Jul 19, 2019 12:15 pm

baldessariclan wrote: AlmostHeavenWV_VW wrote: ?not seeing what you mean? Make sure you're looking at 'compartment air temp' not 'stat air temp'

stat air temp = air temp at the thermostat under the engine (after it has removed heat from engine)
You nailed it! -- I was misinterpreting the thermostat temperatures as the engine compartment temperatures. Makes better sense now, thank you! :-)

you aint the only one, that is a poorly titled graph "stat"? Titles on graphs should be very clear and descriptive of what the graph displays.

Some should not be represented by a graph.

Bug On!