1. Keri

    Keri Leader

    Trabi Thermodynamics!

    So, I've been driving about in Comrade Trabi for practically a year now, taking only a few weeks off to avoid road salt.
    I've become quite familiar with Trabant technology in the process.

    As most Trabant Comrades realize, a Trabi has no motor temperature monitoring system at all!

    Why not? Practically every other car on the road has either a warning light or gauge for motor temperature, so why not Trabants?
    Oh, you say, it's because those poor, starving comrades in Zwickau couldn't afford one! After all, they couldn't afford a fuel gauge either, right?
    No, I suspect the lack of temperature measurement is because it's not necessary. The fuel gauge isn't either, on a car with "reserve" fuel.

    Why wouldn't it be necessary? it is on every other car, so why not ours?

    I believe that it has to do with the way our humble 2-cycle motors operate. They run cold!

    First, our compression ratios are low. Less compression = less power = less heat

    Second, the hot, expanding combustion gasses are expelled from the motor very quickly compared to a 4-cycle motor.
    They start being expelled with the piston only 1/2 way down on the power stroke, while a 4-cycle motor holds them in for the entire power stroke and much of the exhaust stroke.

    Third, the crankcase is being cooled by the evaporative action of the carburetor vaporizing fuel. This can actually lead to problems with keeping the fuel vaporized long enough to still be combustible when it reached the combustion chamber!

    So, a lot of cooling fins and a fan are plenty to keep temperature under control on even the hottest days at full power. No need for a gauge!

    On cold days, keeping the crankcase warm is the issue. That's why the cooling shrouds direct the air past the cylinders and heads and DOWNWARDS past the crankcase.
    Just try to warm that big heavy crankshaft up when it's being "refrigerated" by the carburetor!
    It takes awhile, as the heat of combustion is far away and the roller bearings produce little heat. There's no circulating oil heated elsewhere to warm things up, either.
    The cold crankcase effect leads to fuel condensing in the crankcase and the motor getting very lean at a cold idle. When one speeds up, the condensed fuel/oil mix is blown into the cylinders suddenly causing a sudden, temporary over-rich condition with plenty of smoke.

    One really important thing to consider for those of us in damp climates:
    This cold crankcase effect will cause moisture condensation and subsequent corrosion of the crankshaft and bearings if the motor is not fully warmed up, especially if it is to be stored for any length of time.
    The good news is, 2-cycle oil usually has additives to retard moisture-related corrosion, so that will help some.
    Before putting your Trabi away, it's very important to have the motor just as warm as it will get and preferably on a dry day.
    So, as with any other car, short trips are bad!



    Any thoughts on this tricky and complex subject?
  2. Ditch

    Ditch Leader

    Interesting Keri. I was a bit daunted by the fact that there was no temperature monitoring on the Trabi engine so I fitted a couple of temperature sensors that clamp down under the spark plugs and wired them through to a couple of digital displays in the dash. When choosing the sensors and displays I researched the kind of temperatures a two stroke runs at in the combustion area and came to the conclusion that 200 degrees C was the max. I would see at the plugs so bought stuff that would cope with that. In normal day to day running I rarely see more than 35 degrees on the gauges. It goes up to 90 when I turn the engine off and then leave it a few minutes before a restart because the heat is still coming out of the engine but the cooling has stopped. I took the car up a hill called Sutton Bank in North Yorkshire which is a foot to the floor in second (engine revs just holding) or creep up in first, type of hill and even then it only went up to 42 degrees.

    A couple of other things I notice:

    1. The engine runs hottest when I am on and off light throttles.
    2. The engine visibly cools when I give it full throttle.
    3. The left cylinder runs cooler than the right. This could be a gauge error as they were very cheap.
    Keri and Justin like this.
  3. Aaron

    Aaron Leader

    It may not be necessary as the Trabant was intended for a specific climate where temperature would never be an issue. Bit different for western (primarily American) that have to be able to run in Death Valley. As an engineer, we never do anything temp related for anything in the midwest (where I am, and very similar climate to the Trabbis original sales area).the only time temperature concerns are even raised is for vehicles in the extreme climates
  4. Keri

    Keri Leader

    Cool! Time for a road trip to Death Valley!
  5. Aaron

    Aaron Leader

    Be interesting to really do some modern durability testing..I bet they hold up better than people would think..My guess anyway.
  6. Justin

    Justin Founder Moderator

    Well we might have that chance to find out. It's not uncommon for us to have weeks at a time with temperatures over 115. Last year we had something like 30 consecutive days around 117 degrees
  7. phi

    phi Loyal Comrade

    The possible answers for your statements:

    When you give it full throttle, the air/fuel ratio becomes richer. At part loads, there is sometimes a quite lean mixture which results in higher temperatures and the dangerous noise "Klingeln" (a sort of engine knocking).

    It's well known that cylinder 2 runs hotter. The most engines with serious breakdowns suffer from a defective rod bearing on the ignitions side. The reason is that this side is in a kind of dead zone of the air flux behind the fan and it's less cooled than the other side near the clutch.
  8. vdubbin

    vdubbin Loyal Comrade

    Hi Folks, interesting topic. Though I'd bump this rather start a new topic. I've just been advised by the car's previous keeper (we're in regular email contact, he's a buddy of mine) not to run the heating at full blast, as this will cause the engine to overheat. This is contrary to pretty much everything I know about engine cooling (mainly watercooled, I'll admit) so we're puttingit down to that special Trabi voodoo.

    Has anyone else heard of this? Is there a combination of those 3 plungers I should avoid using in case of doing harm?
  9. Justin

    Justin Founder Moderator

    I just don't see how that would be possible. The heat works by the fan turning, which cools the hot motor and blows that air through the hoses/tubing into the cabin. The same thing is essentially happening when the heat valve is closed, the heat just dissipates through another route. The engine isn't having to work any harder to move the warm air into the cabin; if anything it would cool the engine more.
  10. turbofiat124

    turbofiat124 Premium Member Forum Donor

    Good info. I wondered the same thing about engine temperature monitoring.
  11. Ilija

    Ilija Newbie

    Thats when moving, how does it do in trafic where for example you go uphil and then idle for 7 minutes at a buisy intersection, basicaly extreme trafic at about 40c or 107 farenheut or sometimes a bit hotter, can it do that?
  12. A Spooky Ghost

    A Spooky Ghost Loyal Comrade

    So these can sit in traffic, on an incredibly hot day just fine. I've had mine out many times around 100 F. You will overheat before the car does. Now when they idle for a while, in blazing hot weather. Once you take off it can feel sluggish. This is because it has been not circulating in fresh air(just hot ground air) . It clears out after a little bit-with the fresh air. In summer time the air cleaner is flipped, so it breaths from the hood hinge area.

    The main thing I would worry about is vapor lock. My 601 has the Vent style line, and has a hole in the fuel cap. I consider these a MUST!

    If you don't have a trabi then this next bit is for you.

    The grille is fake! It is solid, with a small hole for the interior air.

    When going up a steep & long hill you can smell the metal of the exhaust getting hot. Then your hit with a nice whiff of what ever is burning off.. :D
    Last edited: Mar 9, 2021
  13. A Spooky Ghost

    A Spooky Ghost Loyal Comrade

    Almost forgot. I've never had a weather related running issue with my Trabi. On comically hot days I prefer to have a aircooled vehicle . Way too many times I've had overheating, and vapor lock issue with older vehicles. Todays modern gasoline boils super easily(even ethanol free)......

    That simple "T" fitting in a Trabant's fuel line is ingenious! So simple, just vent it back to the tank. I've never heard the fuel bubble in these.
  14. Ilija

    Ilija Newbie

    This is confidence inspiring, how do you nean you can smell whats burning off? The front grille? It han never happened to us. Btw we had a first yer 64 trabi 601 when my grandpa sold it due to crisis in yugoslavia of the 90ts it had around 500.000 kms on the odometer and was running good, he said the trick to long lasting, 2 stroke is to not enginebrake very long and shift late beacuse 2 strokes love reving.
    RogerDerSchrauber likes this.

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