r/EngineBuilding • u/Broad_Flower5190 • 1d ago
Mazda Problems with compression and coolant loss through engine block (MAZDA FS 2.0 engine)
About a month ago my girlfriend bough this '97 2.0 Probe for very cheap. It had a running issue (when engine warmed up rpm started fluctuating between 1500-2500rpm). Also when we were buying it I noticed the distributor was turned to retard the timing, I gave it little thought and she bought it anyway cause it was almost rust free.
After a few days a lot of white smoke appeared when I started the car and I noticed the coolant resevoir was empty and there was only air in the coolant tubes. Temp was normal.
We thought the throttle body mechanical sensor that detects if engine is warm enough to lean down fuel mixture was not working due to combustion gasses in throttle body (highest point of coolant system), causing high and uneven rpm at idle.
Then we measured the compression of the engine with my friend. It was bad and uneven - fluctuated from 60 to 90. My friend took the engine apart because we thought we needed to change the head gasket because that seemed obvious. We deducted that the distributor gear connecting to the camshaft was probably incorrectly assembled at some point causing premature detonation and therefore ruining the head gasket. Then they noticed it and retarded the timing because it was correct when we checked it with a stroboscope.
After he lifted the cylinder head he noticed the gasket wasnt very damaged at all, infact everything seemed quite well preserved (low milage engine). The block was not crooked or cracked and there were only some slight pitting and scratches (fingernail got caught). Basically no evidence the engine or gasket contributed to the coolant burning.
The only thing he noticed was that the cylinder head guide sleeve was not protruding from the block (too low).
Could this be the cause for coolant burning? Perhaps cylinder head misaligned because of premature detonation?
What would be our next step?
Pictures from engine, etc:
https://imgur.com/a/RQAaJXR
3
u/Rus-t-bolts 1d ago
Head gasket was likely improperly torqued or the head was warped and wasnt surfaced before reinstallation. You can see where the pistons have been steam cleaned from the water entering the cylinders. Deck the head, new gasket new bolts and send it.
2
u/Ranchshitphoto 1d ago edited 1d ago
Im not familiar with the probes. I have a lot of questions before I can chime in. Did y’all check the coolant level when you bought it? Has it been driving? How many miles are on this engine? Did you clean up the top of the pistons? How did you verify the block or head is not cracked? Whats the oil look like?
How long did it take to burn up all the coolant?
While I’m not familiar with the engine I do not think the head was misaligned. That would be really hard to do while also getting the head bolts in. You’d notice deformed or bent bolts.
What were the compression readings for each cylinder?
You could be chasing a singular issue or several issues that have nothing to do with each other.
Looking at the head gasket photos. There seems to be dark marks that may be combustion build where there shouldn’t be any. Your cylinder head might be warped. Someone before you might have tried to swap it. Failed. Then sold the car.
1
u/Broad_Flower5190 1d ago
Forgot to check coolant before driving it home. When I got it home we immedietly topped it off, maybe got max 500ml in there. Then again maybe the system was filled with emmission gasses, so We're actually not sure how much coolant it burns, but there is a very dense cloud of white smoke and sweet smell when starting. Cylinders also looked wet before disassembly. Oil looked fine after changing, no sign of coolant. Did not do further investigation regarding cracks other than visually checking. Engine is ~200000km (low milage in Estonia lol). Have maybe driven it 300kms total, it drove fine besides not great power when accelerating (did not floor it) and the rpm fluctuation issue. Did not clean pistons.
2
3
u/connella08 1d ago
did the head gasket look to be the original factory one? or did it look like it had been replaced previously and/or recently? I only ask because the gasket surface of that block and head looks like it was cleaned with some sort of rotary tool, which is not good. its possible to create low spots in the deck surface that can cause or promote head gasket failure. I would take the head to a machine shop and have it resurfaced and inspected. The locating dowel being low in the block could have been from attempting to remove the head. maybe the head was dropped back down on it during removal causing it to be pushed deeper.
its entirely possible that the previous owner overheated it, tried to repair it themselves, fucked it up, got frustrated, and sold it.