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]

It seems to me that you guys haven’t yet come to terms with how real and how apparent wear is (when measured) as it relates to temperature. In these charts keep in mind this is cylinder temp, not cylinder head temp.

So let’s put up a couple charts on how engine temp affects wear and how much wear occurs when the engine temp is transitioning.





This 3rd chart is a GM study that shows ring wear on an already running engine accelerate as the coolant temp and oil sump temperate on a dyno is reduced about 1/2 way through the test. Toward the very end of the test the coolant and sump temperate is again raised and the ring wear levels off / stabilizes.



Just to reiterate, I’m not saying the wear is instantaneously going to destroy your engine.

However this shadetree mindset that “I haven’t seen” any reduced life is a fallacy. Without a baseline engine that was operated properly for its life to compare against your engine , you’ll never know exactly how much your particular engine life was shortened. As long as you accept that, do what you want. However - advising others to take on that accelerated wear without informing them about the wear trade off isn’t fair to those that might not know any better.

[JamesM]

It seems to me that you guys haven’t yet come to terms with how real and how apparent wear is as it relates to temperature. In these charts keep in mind this is cylinder temp, not cylinder head temp.

I'm 100% on board with the wear data, this is the reason I had guys replacing thermostats almost constantly while I was at PMB. Id say roughly one in three was coming in with a broken one.

The data points I am adding though (that can also be applied to these charts) is that a "cold start" here at least during the majority of the driving season is generally near if not over 100F+ and that the time to get to 160+ with or without a working thermostat isnt really much different. Assuming at least you are not holding 3k+ rpm immediately after startup. There just isnt enough cooling capacity at idle fan speeds in 100deg ambient (with the asphalt sitting 140-160) to meaningfully slow that process. Air-cooled motors don't have to heat a volume of coolant like a water cooled motor does so this process happens faster and they are not fighting the extra thermal mass due to a broken thermostat in the way water cooled motors do.


The regulation of the cooling system on Type 4s is not incredibly accurate to begin with given that there is no thermostat impacted by oil temperature. The only thing regulating oil flow though the cooler is a pressure bypass and the thermostat controlling air flow through the cooler is on the opposite side of the motor from that cooler only getting the airflow off of the 1-2 cylinders. The flaps/thermostat help the system get up to temp quicker in cold weather but the flaps are generally going to be in the full hot position and blowing air over the oil cooler before the oil is up to temp anyways given how much faster the heads and cylinders heat up vs the oil.

The wear data is valid, but I don't think even in the best case scenario the type 4s cooling system is fully optimized to take the best advantage of that.