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Mon Mar 27, 2023 8:11 am

Why did the oil bath air cleaners have preheat on the fuel injected engines?

Mon Mar 27, 2023 10:51 am

From memory only(?) the 1972 year model had preheated air as an attempt to tackle the new emission restrictions...a bit unsure here, someone can please correct me.

Lars S

Tue Mar 28, 2023 12:46 pm

Lars S wrote: From memory only(?) the 1972 year model had preheated air as an attempt to tackle the new emission restrictions...a bit unsure here, someone can please correct me.

Lars S

I believe you are correct. The non California emissions package....meaning everything but the air pump, lowered compression and retarded ignition timing......was fairly simple and consisted of ways to get through the warm up stage faster as well as the PCV valve system as well as the deceleration shut off.

I think it was only 1972. In the US that probably meant from August 1971 to August 1972 (which became the 1973 model).
Several things changed on the 1973. It was the 412 now and was still D-jet. In late D-jet here in the US, r8ght before the 1.8L and L-jet came out......the 412 with 1.7L switched to a round paper filter unit with no preheat.

Also the sheet metal changed from 1971/72 411 and the warm air chimney located in the firewall sheet metal right next to cylinder #1 went away.

One thing I will try to check....is that may 1973 412 two door coupe ....with 1.7L/D-Jet... .came with an oil bath air cleaner that I swapped to the later round paper filter unit.....but I still have the oil bath cleaner. I will check to see if it deleted the pre-heat or still has it.

Ray

Tue Mar 28, 2023 5:30 pm

Sounds good. Thanks Lars and Ray. I was puzzled why there would have been preheat on a fuel injected engine. Seemed strange to me.

Tue Mar 28, 2023 10:36 pm

Vanapplebomb wrote: Sounds good. Thanks Lars and Ray. I was puzzled why there would have been preheat on a fuel injected engine. Seemed strange to me.
Yes I also thought so at first...but looking at two of my other Bosch multi point injected cars (Golf 2003 1.4 16v and Passat 1995 2.0) they both have warm air arrangement very much the same as the 1972 411.

As a side note only, this is how the new air cleaner was explained when introduced for the -72 model:

Lars S

Wed Mar 29, 2023 2:06 pm

The application for carbureted engines is obvious… but I am puzzled by some FI engines that have it. It isn’t just VW either I suppose. I have seen a vacuum actuated warm air intake on some late 80’s and early 90’s Chrysler fuel injection as well. Must have been emissions related, as you say.

Wed Mar 29, 2023 7:44 pm

Vanapplebomb wrote: The application for carbureted engines is obvious… but I am puzzled by some FI engines that have it. It isn’t just VW either I suppose. I have seen a vacuum actuated warm air intake on some late 80’s and early 90’s Chrysler fuel injection as well. Must have been emissions related, as you say.

I would bet that its there to help out the TS-1 air intake sensor which enriches....you know...I'm not sure whether it gets richer as the air gets colder or warmer. Have to check on that.

But the early injection systems were barely under their own control at cold weather warmup situations. The AAR (air bypass) was crudely controlled. The cold start valve was decently controlled as per when it turned on but not per how much fuel it injected. The TS-2 (cylinder head sensor) drops in ~ 10-15% enrichment in cold weather......so as I found many years ago, unless you are in a perfect state of tune...sometimes you ran pretty rich for a while until fully warmed up. Ray

Thu Mar 30, 2023 4:21 am

So, by that logic, with modern fuel injection systems, the preheat is pretty much irrelevant?

I was also wondering if they found issues in the early non preheat oil baths with the oil being too thick in cold climates, so they added preheat to keep the oil warmer/thinner. The fact that some fuel injected Chryslers with paper air cleaners 30 or so years ago also had preheat kind of blows this out of the water though.

Wed Oct 04, 2023 2:35 pm

In general, I believe the preheat was eliminated when the TSI sensor was added. I suspect that the preheat had been so successful in improving the cold operation of carbureted engines that the engineers just didn't think to eliminate it at first. FWIW, my 91 Vanagon experienced a cold weather variant of Vanagon syndrome that VW didn't offer a cure for and adding the Vanagon syndrome capacitor didn't totally eliminate either. What did eliminate it was making up a hose to lay on top of the block and feed into the air cleaner providing somewhat warmer intake air. The hose got added and removed seasonally.

Wed Oct 04, 2023 5:28 pm

Wildthings wrote: In general, I believe the preheat was eliminated when the TSI sensor was added. I suspect that the preheat had been so successful in improving the cold operation of carbureted engines that the engineers just didn't think to eliminate it at first. FWIW, my 91 Vanagon experienced a cold weather variant of Vanagon syndrome that VW didn't offer a cure for and adding the Vanagon syndrome capacitor didn't totally eliminate either. What did eliminate it was making up a hose to lay on top of the block and feed into the air cleaner providing somewhat warmer intake air. The hose got added and removed seasonally.

Well, in the 411 and 412, TS1 was there (on the engine) from day one. But I think you may be on the right track.

I "think" type 3 got D-jet either a year or a couple if years before 411. And, in the type 3.....originally....TS-1 was screwed into the engine case near the AAR. Going from dim memory here, but the early TS-1s were also calibrated differently (effect wise) in the early ECU.
The gist being that TS-1 in the case was not hot enough or not variable enough. Later in type 3 and early 411/type 4....they put TS-1 into the intake plenum....new ECU calibration....but too cold?....hence the heat riser flap in the air cleaner.
Then they dropped the air cleaner flap pretty quickly (speculation now) because they probably adjusted around the issue with MPS, TS-2 and cold start valve etc. Ray