To disable cooling flaps or not, The endless debate Options

[Superhawk996]

ditch the stat.

Cabman - love ya to death but please stop propagating the ditch the thermostat advice.

The flaps and thermostat are there for a reason.

The majority of engine wear occurs during the warmup phase of operation this is true of all engines and is backed by decades of SAE research and documentation.

Disabling flaps and delaying warmup results in accelerated wear.

Even worse, air cooled engines depend on expansion of the heads to increase clamp load between the cylinder and the head as the engine heats up. Delaying warmup results in more likelihood of blowby between the head and cylinder and between the cylinder and the case.

And even worse yet on a carbureted car where the delayed warmup reduces fuel atomization, and increases cylinder wash down - really accelerating wear and diluting oil.

I’ve read all the anecdotal stuff of “my engine is fine”. You may think so but the reality is you are only looking at a tiny snapshot in time of the engine life and wear. As a hobbyist, you likely won’t ever have the opportunity to compare engine life of engine A that ran properly vs engine B that has the flaps disabled.

And I’ll concede that because a hobby car only gets driven infrequently - that partially negates the wear argument(s).

But let’s not keep propagating the shade tree mindset that the thermostat & flaps aren’t necessary for proper operation and longevity of T4 engines.

Once he’s in there deep enough to identify the cause, it should be fixed properly not jury rigged.

[Superhawk996]

@930cabman

Here’s the thing. The defroster performance has absolutely nothing to do with engine warmup.

The defroster performance is based on the heat exchangers obtaining heat from the engine exhaust heat.

Regardless of the overall engine operating temperature, the exhaust gas exiting the combustion chamber is in excess of 600-800F almost instantaneously.

Just because you have heat doesn’t mean the engine is at operating temperature.

You also keep going back to the analogy of your engine. Engine wear from running cold doesn’t manifest immediately. Unless you have multiple engines that have been run to failure or end of life to compare to a singular data point of your engine at a few thousand miles is practically meaningless.

How many miles on your engine?

I think we both want the same thing for Ron, a functional car to drive.

The thing is for him to disable the flaps, he would still need to drop the engine and resolve what ever is limiting his flap movement and preventing them from getting to full open.

[930cabman]

@930cabman

Here’s the thing. The defroster performance has absolutely nothing to do with engine warmup.

The defroster performance is based on the heat exchangers obtaining heat from the engine exhaust heat.

Regardless of the overall engine operating temperature, the exhaust gas exiting the combustion chamber is in excess of 600-800F almost instantaneously.

Just because you have heat doesn’t mean the engine is at operating temperature.

You also keep going back to the analogy of your engine. Engine wear from running cold doesn’t manifest immediately. Unless you have multiple engines that have been run to failure or end of life to compare to a singular data point of your engine at a few thousand miles is practically meaningless.

How many miles on your engine?

I think we both want the same thing for Ron, a functional car to drive.

The thing is for him to disable the flaps, he would still need to drop the engine and resolve what ever is limiting his flap movement and preventing them from getting to full open.

Point made, if I can get it on the list I should probably just get er done. And yes, defrost has little to do with engine temps

To Ron's issue, I was hopeful the tin could be removed in place but I have never attempted this operation. Surely this work is much simpler with the engine on the bench. Is the consensus his overheating is due to closed flaps?

[JamesM]

I think you both have points that are valid to some extent, but I think context has been left out of the discussion.

Here are some of my thoughts on it:

First I agree that I don't think the Germans put unnecessary parts on the car. That said though they built a car that was intended to be used in ways and across a wide range of environments that I don't think a whole lot of 914 owners actually use them in anymore.

A winter in Germany and a summer in Southern California have different requirements. At this point I think most if not all 914 owners avoid even driving in the rain, let alone sub 20 degrees and snowing.

Why is this relevant? Well, living in Utah and having driven 914s in conditions that are more extreme on both end of the spectrum I have some data points to add. Specifically on a 100 degree day in summer I wont ever see the thermostat closed, but in the winter say cruising down the mountain in 10 degree weather, I wont see it ever open, AND even then its a fight to keep temp in the heads.


So. My personal opinion is that it is BETTER to have the thermostat installed and working, or at least there is not a downside to it because that gives you the best possible outcome under all conditions. BUT given most 914 owners are not driving in conditions that would keep the thermostat closed while driving and that the time it actually spends closed even on startup in hot weather is minimal its probably not the end of the world to go without it. Unless of course you plan on driving down mountain roads in a Utah winter in which case you absolutely want it functioning.

Having the air flaps installed properly though is ALWAYS a must. IDK where anyone got the idea that it was ok to remove the flaps completely but I have seen that done more than a few times.

[Superhawk996]

BUT given most 914 owners are not driving in conditions that would keep the thermostat closed while driving and that the time it actually spends closed even on startup in hot weather is minimal its probably not the end of the world to go without it.

James - I largely agree with your position in a pragmatic sense. Nothing is black and white. The accelerated engine wear isn’t immediately perceptible and will only be evident over the (shortened) life of the motor

However what frustrates the hell out of me is the continued reliance in these threads on one off anecdotal accounts. “My car” or “I saw”.

Here’s the thing. Cold start and warmup wear has been studied extensively by the OEM’s using radiographic techniques to monitor engine component wear during start and warmup operation. There is extensive dyno testing and end of life tear down analysis to know with certainty that not operating in the desired temp range shortens engine life. It just isn’t debatable.

I personally used to attend end of life teardowns, warranty failures, and multiple life (200,000 - 300,000 mile motors) about once a month early in my career. You can defiantly tell the engines that were abused by lack of maintenance, sludged oil, and granny cycle (short trips that never come up to operating temp).

I’ll be happy to start posting some SAE paper numbers going back to the 50’s. But the reality is they are $39/paper to download and I can no longer get them for free at work since I’ve retired.

Would anyone here simply take the thermostat out of your daily driver? I mean after all, if people believe it really doesn’t hurt . . . (IMG:style_emoticons/default/poke.gif) Why have it there to potentially fail. The thermostat on a 914 is no different. The 914 thermostat when operating properly isn’t a binary thing that is just open or closed. The 914 thermostat modulates to keep engine temp in a desired range just like a water pumper thermostat.

And as far as the wholesale removal of the flaps, it seems that at least is well enough understood that we aren’t seeing the complete removal that we used to see in the 80s & 90s.

[JamesM]

Would anyone here simply take the thermostat out of your daily driver? I mean after all, if people believe it really doesn’t hurt . . . (IMG:style_emoticons/default/poke.gif) Why have it there to potentially fail. The thermostat on a 914 is no different. The 914 thermostat when operating properly isn’t a binary thing that is just open or closed. The 914 thermostat modulates to keep engine temp in a desired range just like a water pumper thermostat.

Having driven both water cooled cars and 914s with failed thermostats there is an observable difference in their temperature control behavior. In my experience when a water cooled thermostat fails the engine never fully comes up to temp, even in the middle of summer. This for sure will cause ongoing accelerated wear, bad gas mileage, etc. In warm weather, I haven't seen that a 914 comes up to temp noticeably slower with a broken thermostat. In the middle of a Utah winter it absolutely does but when thermostats have failed on me in the summer, I don't even notice their failure unless im physically inspecting the engine. the 914 thermostat is a lot more impacted by ambient temperature possibly due to the 914 thermostats placement more or less in ambient air. Yes they modulate temperature but the range in which this modulation occurs only seems to exist at colder ambient temps.

Again though, no one should intentionally remove a working thermostat, it accomplishes nothing positive. I'm just saying if your thermostat fails in the middle of summer it probably isnt reason to stop driving your 914 until you can source a replacement. Given its going to take most people 20 years to put 100k on their 914s these days and things like carb conversions, worn out d-jet setups, cylinder cooling fins that have never been cleaned, missing engine tin grommets, etc are contributing far more to engine internal wear than an extra 60 seconds of warm up time.

[Superhawk996]

the 914 thermostat is a lot more impacted by ambient temperature possibly due to the 914 thermostats placement more or less in ambient air. Yes they modulate temperature but the range in which this modulation occurs only seems to exist at colder ambient temps.

Here’s the thing - what you observe while the car is sitting static isn’t the same as what’s going on while driving.

Because the bellows is largely in the ambient air steam it is getting much cooler airflow while driving (partially closing flaps) than when you see it while then vehicle is sitting static and only getting hot engine air from above.

Sure on a 100+ day - once warned it won’t modulate much. However, don’t overestimate the number of cars being driven in 100F + temps especially those without A/C.

[era vulgaris]

the 914 thermostat is a lot more impacted by ambient temperature possibly due to the 914 thermostats placement more or less in ambient air. Yes they modulate temperature but the range in which this modulation occurs only seems to exist at colder ambient temps.

Because the bellows is largely in the ambient air steam

But, it's not actually supposed to be in the ambient air stream. On ACVW's it's protected from the ambient air stream by the sled tins, and on 914's it's protected from the ambient air stream by the lower engine tin (the angular looking one with the half-cylindrical indent for the shift rod). However since these lower tins are missing from most 914's, the thermostat ends up in ambient air where it really was never meant to be.

I still 100% agree that all of these parts need to be there (just got in this same discussion recently on the samba because alot of people don't understand how critical a fast engine warm up is), but if you want the system working exactly as it should, that lower engine tin also needs to be in place.