Overheating lawnmowers

[philnotfil]

This is the second one in a row, so I'm guessing it is something that I'm doing wrong

Current mower is a Murray 20" with 6hp B&S engine. It replaced a 4.5hp B&S powered mower (forget who made the deck, never had to work on that part of the machine).

With both mowers, after about 90 minutes of use they would overheat and freeze up. I got the larger engine hoping that it would make it through the whole yard (just over 1/2 acres of grass).

Would a newer mower have some magical technology that would get it through the entire job? These have both been 10+ years old, bought used. The previous mower had an air filter casing that leaked, so dirty air could get around the side of the filter, the carburetor would get gunked up pretty quick, but that was in addition to the overheating issue. (I think)

Changed the oil in the current mower this morning, checked it when it froze up, still at good levels, but dark black. Not thick, just dirty.

I really want to be able to go out to the shed, pull out the mower, start it up, mow the lawn, and then put it away. Taking it apart and putting it together again before I mow the lawn is getting old. (it's a nice feeling to bring it back to life, but it also puts me mowing in the middle of the day instead of mid-morning)

So, what am I doing wrong? Is there a maintenance step I am missing? If I get a bigger mower will it be able to make it through the whole job in one go? Do I just need to do this in smaller chunks?

 

[mechanic mark]

Manuals - Service - Support - Murray Enter model number and go to troubleshooting section. Post engine manufacturer as well as all numbers from engine: example for B&S engine- model xxxxxx, type xxxx, trim or code xx.

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[philnotfil]

Manuals - Service - Support - Murray Enter model number and go to troubleshooting section. Post engine manufacturer as well as all numbers from engine: example for B&S engine- model xxxxxx, type xxxx, trim or code xx.

Murray 20515x8a, nothing shows up on the Murray site, but if I just google it I get bunches of pages of parts for it. So that is the right number, it just isn't on their site, too old maybe?

B&S model 12H802, type 3172, trim E1. Owner's manual with no useful information for my particular problem. Check oil every 5 hours of run time, change oil every 50 hours. It says that I should clean the combustion chamber, I can do that some time later this week and see if it makes a difference. Inspection through the spark plug hole shows some carbon buildup, but nothing excessive (from what I could see, I reserve the right to find more problems when I open it up :smile.

I don't have as much experience with small engines, so I'm worried that I'm missing something.

 

[aandpdan]

What oil are you using?

Make sure that the blower housing are clean. Take it off, remove any grass/leaves/debris/rodents from the cooling fins.

Are you using E10 or less? E15 and higher can cause problems.

 

[exotion]

Oil viscosity is important for cooling engine, the heat sinks around the head and exhaust need to be mostly clean probably a little grease but if they are seperated you are ok. Flywheel needs to be clean same with engine block. Oh ya check spark plug to make sure its the right one And properly gapped

Most times I've ever seen over heating is wrong dirty oil, rats nest under shroud.

 

[Wildcat]

Let me start off by asking a dumb question.

Are you at full throttle when you cut grass? If not that might be the problem.

As for the oil being dirty....its oil. I will blacken after the first use or two and it is normal to see that. As asked above, what grade you using? Most manuals state that 10W30 should be used.

 

[philnotfil]

SAE 30 oil, freshly changed, new air filter and new spark plug as well. Ran great for the first 80 minutes, the last ten minutes it had started hunting a little (revving up and down for no good reason). I had been adjusting the lower screw that is supposed to deal with that, turn the screw a little, do another line of grass, and then it didn't start one time, didn't even turn. (only two lines left, at least they are off to the side)

With some time to think about it, there is no oil filter, so I should expect the oil to start looking dirty right away. If I had changed the oil in my car and then seen oil like that after 90 minutes I would be stressed.

I try not to run it at full throttle, after 90 minutes it tears up my hands, and I hate wearing gloves. Maybe 2/3rds of the way to full throttle

I'll take off the shroud and see if I have any debris, or rats, under there.

 

[exotion]

First, mowers are designed to run full throttle no less. Running it lower makes the engine not cool effecient, cut effecient, and shortens engine life. Second if your mower is hunting or surging I would probably take carb apart and clean it. Or replace it.

That seems like it might be your problem there may not even be overheating. Your carb is probably just gummed up.

 

[philnotfil]

First, mowers are designed to run full throttle no less. Running it lower makes the engine not cool effecient, cut effecient, and shortens engine life. Second if your mower is hunting or surging I would probably take carb apart and clean it. Or replace it.

The full throttle thing is good to know. Maybe I'll put some foam on the handle so my hands aren't so torn up by full throttle on the machine.

That seems like it might be your problem there may not even be overheating. Your carb is probably just gummed up.

Unfortunately I had just cleaned it out (when I did all the other stuff). If it is getting gummed up after an hour of run-time, I probably just need to get a new machine. I'm not real excited by the idea of taking it apart and cleaning it out twice to be able to mow the lawn once

 

[philnotfil]

Took off the shroud and cleaned things out. A few leaves, some dirt, but nothing exceptional.

Purposely ran it without messing with the oil or carb, trying to isolate causes. Started up on the first pull, no hunting, everything seems fine. I'll rule out oil and carb as problems, it does seem to just be an overheating issue.

I can do the yard in smaller chunks to avoid the overheating. It will look funny until the whole job is done, but I can live with that.

But that takes us back to the original question, if I get a newer pushmower, will it make it through the entire yard in one go?