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I have an old Skoda Estelle with its original carbureted engine. It has been working so far. This car doesn't have a thermostat installed.

Timeline:

A few days ago, I realized it was consuming too much water and running a bit hot.

A few days later, I found out the water was coming into the oil sump. It contaminated the oil and made it look like the famous "mayo". I changed the oil.

Today, I drained the oil: no mayo!

Observations:

During a very short trip, the water temp hit 110C. The purge hole in the radiator flows water that is much less than 110C.

There is quicker, more substantial overheating now.

Questions:

  1. First I thought it was bad head gasket, but why does it no longer looking like mayo?
  2. Could this be a clogged radiator?
  3. Any ideas, before I disassemble the engine?

BEFORE AND AFTER :)

before and after cleanup

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    Aram, I'm guessing you speak Spanish. I made some edits based on Google Translate (carter = oil sump). Please feel free to edit if I miscommunicated your intent – Zaid Oct 26 '16 at 2:35
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    good god, i was thinking in español and writing in english :) thanks for the edit – Aram Alvarez Oct 26 '16 at 2:44
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Some thoughts:

  • think about interfaces where could coolant and oil mix. The head gasket is one place but there may be another place like an oil-water heat exchanger.

  • Under normal circumstances I would expect the oil to flow into the coolant reservoir and not vice versa due to pressure differentials (oil is usually at a higher pressure than coolant). In your case it seems that the coolant loop is at a higher pressure than the oil loop. Lack of coolant flow can quickly raise temperature and pressure beyond what the system was designed to be at.

  • a few days may not enough for the oil to take on a mayo-like texture and appearance

    OR

    the mayo effect only occurs at very high temperatures. 110 deg C isn't hot enough for that to happen

  • the lack of coolant flow through the radiator could be due to a clogged radiator or a failing water pump (eroded impellers, leaking seals). As there is no thermostat on this vehicle that is one less failure mode to worry about

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  • Today I disassembled the engine and to my surprise, the head gasket looks ok, however both #2 and #3 chambers are quite loaded with carbon. #1 and #4 have less carbon, and valves looks like light brown or beige. I see a missing bolt next to #2 and #3. OR water was getting into #1 and #4, explaining the more pristine cambers OR the head gasket was failing between #2 and #3. Head flatness is ok. I found lots of dirt glop in the water holes around the cylinders. The mechanic or owner applied grease to the head gasket...maybe it was the overheating cause. – Aram Alvarez Oct 27 '16 at 3:34
  • @AramAlvarez that crud in the water holes could very well explain the lack of coolant flow and subsequent overheating. Did you check the engine block surface for straightness? – Zaid Oct 27 '16 at 4:58
  • This engine uses wet cylinders that btw I will change. The other thing is that the block has 2 missing bolts: one was broken right there almost in the surface, the other is the hole with bad threads. I managed to extract the first one by arc welding another bolt I previously sharpened its tip like a pencil. For the second I will need to get an oversize bolt. I guess missing bolts also made the gasket leak whenever it liked :) sometimes yes, sometimes not, depending on water pressure affected by overheat...or sort of hehehe – Aram Alvarez Oct 29 '16 at 3:40
  • @AramAlvarez could you clarify what you mean by "wet cylinders"? Thanks – Zaid Oct 30 '16 at 2:22
  • Wet cylinders, floating cylinders...those cylinders that are separate pieces and gets inserted in the block, they are not part of the block as usually car engines have :) A leaking problem may be because the "seat" where these cylinders gets inserted at their bottoms gets, well, leaky :) this engine uses liners to even the cylinders to the engine head. I also see the previous owner put silicone to make a gasket there. Maybe there were the main spot for leaking to the oil sump. This engine is in pitiful conditions, I wish you guys could see photos of its head for instance :( terrible. – Aram Alvarez Oct 30 '16 at 2:53
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Alright! Mistery solved, engine was overheating because several events:

a) it was passing water to the oil sump because the head gasket got damaged, because:

b) two missing bolts in the head! One was broken inside its hole, the other got the hole threads damaged

c) passing water to the oil (and vs.) made the water sticky, attracting more dirt, because:

d) the previous owner used tap water! so from cylinder 3 to 4, the block got so much SOIL (yes, soil!) that made water impossible to flow, making the engine to overheat, and we go up to the point a) in this list :)

Today I took the wet cylinders out. Lots of soil after #2 towards #4. #4 was epic, like a boot sole from an outdoors walk under the rain hehehe. Even the cam followers for that piston had soil inside!

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