Mower barely runs and has blue exhaust

Question

I have a Cub Cadet 1529 which I recently maintained in several different ways.

1. I changed the oil and filter a few weeks ago. I put 5W-30 in but had a really hard time telling if/when it was full because someone really needs to invent a better way to see oil level than a stupid inaccurate dipstick. I ended up removing some oil after I saw it leaking. I still can't tell if it's too full or not. I mowed at least once (1/2 acre) (maybe twice) without any major issues other than some oil leaking while sitting in the garage. The oil level seems like it's FULL or possibly overfilled but as far as I can tell, it's definitely not LOW.
2. I replaced the PTO belt (it was old and worn out and finally broke). I have mowed about 1/4 acre with it without any major issues.
3. I replaced the air filter. I can't possibly imagine how this would have caused any issues.

Today when I went to haul some stuff around my yard, I noticed the engine wasn't running well, as soon as I started it up. I could only go about half-throttle before it stopped speeding up. Blue smoke was coming out consistently. The choke sounded like it was going to kill the engine. I tried driving it around a little bit to see if the slight angle was causing a problem but it didn't get any better. I turned it around and drove it back into the shed.

I have a feeling it has a blown head gasket which I will have to figure out how to fix, I suppose... is that the most likely issue? How hard is this to change myself?

Answer 1

Blue smoke means it's burning oil.

This could be from you overfilling the crankcase but if it is an older engine it may have been burning a little oil before the oil was added.

The key here is, was it running okay after the oil change? If the problem started afterwards it then that is the likely cause.

Most small engines like that don't have an oil pump and would have no way to get oil past the head gasket. Even automobile engines don't normally suck oil into the cylinders past the head gasket. It is more likely the piston rings and valve seals are worn so badly that they are allowing oil to pass into the cylinder. Especially if it is overfilled. Watch the first part of this video about splash lubrication. Most older lawn mowers would use this method.

Your first step should be to verify that the oil is NOT overfilled. It could be forcing it past the valves into the cylinder. Your tractor data says it takes 1.8 quarts. If you put more than that in it, then you overfilled it. Your problem could be fixed with a proper level of oil in the crankcase.

Good luck!