Oil operating temperature in small engines.

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Yesterday it was pushing 95 deg F here in Northern Alabama. It was time to mow the lawn, so out came the '94 vintage John Deere STX38 with the 12.5HP Kohler engine and hydrostatic transmission. I use 10W-30 oil, mostly Mobil1 but have put the odd half-quart of left-over dino 10W-30.

Since it was so hot, I got out the infrared heat gun and took the temperature of the outside surface of the oil filter as I was mowing. (Yes, I targeted the NAPA sticker, not the shiny can, knowing that the IR gun won't work on shiny surfaces.)

After about 30 minutes, it had hit 200 deg F.

After about 60 minutes, it had hit 225 deg F.

When I finally pulled into the garage after an hour and a half of mowing, it was reading 250 deg F. I could feel the heat radiating off of the engine itself.

I let the engine run at full throttle with no load for about 5 minutes in the garage. The temperature remained close to 250 degrees F. I was curious to see if 5 minutes of no load would drop the oil temp.

I was both surprised and not surprised that it had gotten this hot. On one hand, I know small engines that air-cool don't have active temperature control, so I'm not shocked. As we hit warmer weather, the engine will naturally run hotter. Yet, on the other, I'd never have guessed it would hit 250 deg F, as I would have though it would have sufficient cooling to not get that hot.

I've always been an advocate for quality oils in air-cooled equipment and personally have always run Mobil1. With the Mobil1, I can run a full season (50 hours or so) with the oil staying very clean. In fact, it almost looks too good to change at the 50 hour mark. But since it sits all Winter, I always change the oil/filter in the Spring regardless of appearance. It takes maybe 2.5 quarts and the NAPA Gold filter is under $5 from site sponsor Fleet Filter.

Now that I've seen this result, I have just a little bit more data to back up advocating quality oils for air-cooled small engines. Note that I'm not saying that a cheap oil wouldn't work as well, I'm just saying that I feel more comfortable using what I use.

thanks much,
ben
 
Thanks for that info. I used to have a "Harley Davidson" type oil temp gauge. 260 was a normal average after shutdown. I am sure it got hotter when running, but I simply could not touch it to get the oil filler off and insert the probe.

Now, you got me thinking about using my infrared thermometer too.

One thing I discovered, the surface must be flat black to get the highest reading, in other words I'm not sure about the accuracy of the infrared thermometer on different colored surfaces.

Chris
 
Change the oil in the Fall,after the last mow. That way, the oil in the crankcase will be clean all winter. .02.
 
Originally Posted By: Cujet
One thing I discovered, the surface must be flat black to get the highest reading, in other words I'm not sure about the accuracy of the infrared thermometer on different colored surfaces.


Funny you ask this! I asked the same question a month or so ago when we had some people at work with a calibrated source. Turned out it was actually close - within 5 degrees at about 400 deg F.

Most of them are calibrated for a surface emissivity of 0.9, which covers most non-reflective surfaces. If the surface is shiney (like stainless) or reflective (like any color gloss paint), they will be off, as they are reflecting IR from other sources.

Solution is to put a peice of masking tape on the shiny surface. Works great and has an emissivity of right around 0.9. Actually, it works great until the tape burns off. Ha ha!

later,
b
 
I'll admit that when I hit 250 deg F, I had been mowing some pretty high grass rather agressively. Hopefully I'll mow again this weekend in cooler weather and see where it runs...
 
i installed a oil pressure guage and as soon as the oil gets hot i get 50 psi...i also use MOBIL 1 [10 W 30 ]so i am not too concerned if my air cooled tractor runs hot .i also change the filter and oil before storing the tractor for the winter ..don't forget that old used oil contains a lot of harch chemicals that can damage the bearings during winter storage..my 02
 
I been running a 5500 watt Generator for 3 days.
Crankcase oil temp has run from 199°F to 212°F.
I estimate the generator is running at approx. 60% of it's max load.
I change from Rotella 10w-30 (was out of the RT 10w-30) to PP 5w-30 and the temperature were the same.
 
That sump temp really isn't as bad as I thought it would be after hearing your conditions. I know a lot of motorcycle owners who run oils at 220F + sump temps for hours at a time as they blow down the highway. Interesting to read about how the oil temperatures didn't change with the oil change.
 
Hey gang,

Did some more measurements last weekend. It was about 5 degrees cooler, but the grass was EXTRA tall and EXTRA thick after the rain we've been getting lately. Lawn looked like a wheat field - was getting evil looks from the neighbors, but if they are so concerned they can come over here and mow for me any time they like!

Saw 275 deg F after about two hours of sheer mowing punishment. Oil looks as clean and as fresh as when it came out of the bottle.

Oh yeah, hit a dog bone in the yard and bent a blade. The whole thing shakes like a Chinook helicopter spinning up the rotors when I engage the deck. Guess what I get to do this weekend? Glad I have a spare set of blades 'cause this pair is done for. I've never been so happy to have neglected changing them at the beginning of the mowing season. For once, a LACK of maintenance pays off! Ha ha ha ha.

thanks,
ben
 
I get the same feeling after I hit one of my son's baseballs hidden in the tall rass--expletives deleted
After he hears the sound of baseball meeting blade, it becomes impossible to find him. Wonder why?
I can laugh now, but it wasn't very funny when in the dark, I ran over one of his wood baseball bats -if he wasn't so darned good at baseball, I'd be crazy over this
Steve
 
Re: Steve and various sports related gear incidents...
Yikes!! A friend of mine hit a golf ball (his neighbor's a golfer...) while mowing - the ball shot out the discharge chute, ricocheted off a brick wall and whizzed right back past his head. After changing his underwear, he went and had a chat with said neighbor..

I also did the same thing in my own yard (I used to be a golfer). Ran over a ball, the blade must have caught it just perfect - it soared up over my house like one of Tiger's shots.
Fortunately, it didn't hit anything, or... wife ->
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