Will 15W40 Cause My Poor Little B&S To Overheat?

[Oldwolf]

I just replaced the old 10W30 synthetic in my B&S 3.75HP (Model 10D900) powered Sears pressure washer and now it appears to be overheating. As you know pressure washers run their engines hard (maybe 100% power output, I don’t know) and I am wondering if the 15W40 I just put in might be causing the problem. I would be surprised if it was, but this oil is thicker and will make the poor little engine work even harder. Until now I have not a lick of problem with this engine.

So, here is what happened. Yesterday I got the pressure washer out and fired it up like normal, happy in the thought that I had fresh Delvac 1300 in the sump. Outdoor temperatures were 90F+.

After maybe 10 minutes of nonstop washing I noticed the RPM’s were beginning to drop. I let off on the washing and the engine, now unloaded, ran fine. Went back to washing and after a minute or two the RPMS started dropping again.

This cycle went on a few times until the engine just died. At this point the engine felt really hot, water would boil when put on the lower half of the crankcase. But the engine started up again after giving the priming bulb a few pushes and the starter rope a few tugs. Maybe Vapor Lock?

My first thought was fuel starvation, so I will pull the carburetor and check the drop tube screen for blockage. The air filter is clean and I haven’t yet pulled the sparkplug to take a look at it. I'm using my usual gasoline with StaBil in it.

But the boiling hot engine has me concerned about the oil. Maybe I should go back to 5W30 synthetic. What do you think?

 

[Steve S]

Hard to say as I have a pressure washer from Home Depot that runs 4,000 psi and 4 gallons per min. and it has had nothing but 15w40 in it without any problems. But then I never realized that oil choice is the cause of every mehcanical and electrical problem on an internal cumbustion engine after reading many posts on this website. It would be esay to change out the oil as it is about half a quart.

 

[SuperDave456]

I can't imagine that a change in grade would cause your symptoms.
I too think it has something to do with your carb.

Maybe run a little bit of fuel system/carb cleaner through it?

I would also check the spark plug. I change mine out whenever they begin to look funky, which is before they start giving me an issue.

BTW, I run Rotella T6 15w40 in my lawnmower and it seems to hold up great.

 

[94MaxGXE]

LINK

You say you just got it out. Don't forget that mice love to nest in motors like that. Check example link above.

 

[boraticus]

Can't see oil being the problem. Boiling point is only 212 deg. F. Air cooled engines run much hotter than that. It can be anywhere from 240 to 300 degrees F. Sounds to me like you have a fuel delivery problem. Possibly a restriction in the fuel lines/carb, fuel cap vent or maybe even a vapor lock caused by heating the fuel.

 

[Oldwolf]

Originally Posted By: boraticus
Can't see oil being the problem. Boiling point is only 212 deg. F. Air cooled engines run much hotter than that. It can be anywhere from 240 to 300 degrees F. Sounds to me like you have a fuel delivery problem. Possibly a restriction in the fuel lines/carb, fuel cap vent or maybe even a vapor lock caused by heating the fuel.


I have a hard time believing the oil is causing the problem also. Probably just a coincidence that right after I changed it this started happening.

I'll remove the carb, clean it out, and also look at the plug.

But what would cause vapor lock now, if not overheating of the engine? I suppose if the fuel system was running lean that might cause overheating under full load.

 

[Steve S]

A late thought how is the gas cap vent?

 

[Oldwolf]

I loosened it after it first died, didn't hear a "sucking" sound. Not I good test I know. How do you test a gas cap anyway, other than replacing it?

 

[Steve S]

See how the engine runs with the cap loose . I am wondering if the vent is clogged . My lawn mower has a clogged vent if I thghten the cap too much it quits running till i loosen the cap a bit.

 

[gd9704]

Originally Posted By: 94MaxGXE
LINK

You say you just got it out. Don't forget that mice love to nest in motors like that. Check example link above.




This has happened to me a few times. Luckily, when I started the engine a bunch of grass blew out to warn me!

 

[greenaccord02]

Sounds to me like a fuel delivery clog. Prime it HARD a couple times and that might get things moving, but you'll probably have to take the carb apart and do a proper job.

As far as the heat goes, you could remove the cowling and see, but I doubt it's anything other than normal operating temp. You're just noticing it because it was giving you trouble.

 

[Oldwolf]

Originally Posted By: greenaccord02
Sounds to me like a fuel delivery clog. Prime it HARD a couple times and that might get things moving, but you'll probably have to take the carb apart and do a proper job.

As far as the heat goes, you could remove the cowling and see, but I doubt it's anything other than normal operating temp. You're just noticing it because it was giving you trouble.


Sounds like good advice.

 

[JimPghPA]

Could be the flap valve below the carb, they go bad on B&S. Very likely this is the problem ,this show up the first time you use it after it was stored for a while.


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An unlikely but still possible problem would be a sheared pin on the crank and the timing is way off.

 

[Oldwolf]

Originally Posted By: JimPghPA
Could be the flap valve below the carb, they go bad on B&S. Very likely this is the problem ,this show up the first time you use it after it was stored for a while.


You might be right. I took the carb apart and cleaned everything out with carb cleaner. I never have seen a flap valve like that in a carb btw. Anyway, I put it all back together and it seems to run fine. I might buy a carb rebuild kit for it anyway and have it ready should the problem re-arise.

 

[greenaccord02]

It's always good policy to keep an extra carb kit handy. You never know when one may decide to give out on you. They usually just cost $2-$3 apiece so it's not a terrible expense.

 

[jeff194]

You could try a little MMO in the gas. It worked last fall when I started my leaf blower, and it sounded like it was starving for fuel.