Riding lawn mower boiling hot oil, add oil cooler?

Joined
Feb 24, 2005
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304
Location
eastern NewMexico
The machine is a craftsman 18.5hp V-twin air cooled, with 42 inch deck. I normally use synthetic 10w-40 or 20w-50 motorcycle oil. I run this thing hard.
I knew the oil got hot it seems to get cooked fast, but it looks like it can deep fry. I went to change the oil on the mower, I went a lap around the field to get the oil nice and churned up but not quite maximum temp. Then I pulled the oil plug and dumped it into my oil catch pan and on contact with a little water in the bottom of the catch pan it boiled it. Im glad I was wearing rubber gloves because some of that oil got on my finger.
So im thinking oil cooler with a thermostat?
The 18.5hp kohler V-twin has an oil filter and pumped oil system.
I was looking at replacement engines and they are over $1,000 so dont want to do that.
Anyone ever add an oil cooler to a riding lawn mower?
I have a transmission cooler that would be perfect, might add a fan but will try with out the fan. All I would have to buy is a sandwich adaptor and get some lines.
 
Joined
Oct 23, 2005
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Boiling water only says the oil is at or above about 212°F. That's why they specify a 40 or 50. I'm thinking they designed it right, take a sample and send it in, see if the oil is holding up. What is the recommended change interval?
 
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Georgia/Retired
Amsoil claims that their 20W-50 V-Twin motorcycle oil excels at protecting in extreme heat. Maybe give it a try. As for the air-cooled V-twin, remove the cowl and make certain that there is no debris blocking the housing or cooling fins. Even in New Mexico in August the air flow should be adequate to keep the engine within design parameters.
 
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Feb 6, 2021
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Massachusetts
The machine is a craftsman 18.5hp V-twin air cooled, with 42 inch deck. I normally use synthetic 10w-40 or 20w-50 motorcycle oil. I run this thing hard.
I knew the oil got hot it seems to get cooked fast, but it looks like it can deep fry. I went to change the oil on the mower, I went a lap around the field to get the oil nice and churned up but not quite maximum temp. Then I pulled the oil plug and dumped it into my oil catch pan and on contact with a little water in the bottom of the catch pan it boiled it. Im glad I was wearing rubber gloves because some of that oil got on my finger.
So im thinking oil cooler with a thermostat?
The 18.5hp kohler V-twin has an oil filter and pumped oil system.
I was looking at replacement engines and they are over $1,000 so dont want to do that.
Anyone ever add an oil cooler to a riding lawn mower?
I have a transmission cooler that would be perfect, might add a fan but will try with out the fan. All I would have to buy is a sandwich adaptor and get some lines.
Just put Mobil 1 15w50 in it if you're concerned, it can take heat much hotter than that. If passenger cars can go hundreds of thousands of miles with 220°F+ oil temps I think your mower will be just fine. Oil needs to be hot for the AW/EP additives to work and to boil off water (a byproduct of combustion, don't forget). Trying to cool it down will likely result in sludge buildup.
 
Joined
Nov 22, 2013
Messages
157
Location
York, Pa
Make sure the cylinder cooling fins and fan blades are clean.
Do this first then try it . My 20hp V-twin Honda gets pretty hot but it has never been a cause of concern in the 10 years I've had it. Mobil 0-40 is what it gets and a good cleaning with the air compressor blow gun a few times a summer keeps me and the engine happy.
 
Joined
Jan 22, 2011
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6,006
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Ohio
Yes they all run hot but you are worrying over nothing. Spend the time to remove all your heat shields and make sure all the fins and everything else is clean, free of packed in grass and grease. If you ever took off any shrouds, put them back on. To install some kind of oil cooler is ridiculous.
 
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Americus, GA
Air cooled mower engines need to be run wide open. Have you ever removed the engine shroud and cleaned the cooling fins? Do this and put the shroud back on. 15w40 or 20w50 oil is fine. A clean engine and cooling fan is going to help a whole lot.
 
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Joined
Aug 19, 2010
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Champlain/Hudson Valley
One more for clean fins etc.

A pal has to place a bag of mothballs atop his engine IN SEASON because mice will nest there.

Once I saw he missed one and the engine (23hp Kohler Command) ran on. After removing a small nest it ran just fine.
 
Joined
Jun 19, 2020
Messages
776
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Iowa
As others have stated remove your engine covers and check for debris. I bought a used Deere LT150 last year. It was smoking a little and burning / dripping oil.

This spring I pulled off all the covers to find the issue. Every nook and cranny was full of oil soaked dirt and grass. After a couple hours of cleaning a new main crank seal and valve cover gasket the problem is solved. The mower puffs a little smoke at start up but other than no signs of burning and no dripping at all. The mower seems to be running cooler.

I’ve cut grass since the spring and the oil (Super Tech FS HM 10w30) has hardly changed color. Last season I used Mobil 1 HM 10w30 and it got surprisingly dark. I’m guessing from heat because the internal were remarkably clean when I tore it apart.

just my $0.02
 
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Close to Sierra mountains
Your idea for a oil cooler has merit except you will not have good air flow for it to be worth while unless you invest in one with a fan. You did not post if your mower has a generator or if it 12 or 6 volt electrical system which would also determine if you can even use a fan/cooler set up. You can consider to use a cooler that has a larger surface area like a radial fin design which will also increase the oil capacity slightly depending on the size. More surface area means more hot oil is cooled.
 
Joined
Jul 14, 2020
Messages
873
The machine is a craftsman 18.5hp V-twin air cooled, with 42 inch deck. I normally use synthetic 10w-40 or 20w-50 motorcycle oil. I run this thing hard.
I knew the oil got hot it seems to get cooked fast, but it looks like it can deep fry. I went to change the oil on the mower, I went a lap around the field to get the oil nice and churned up but not quite maximum temp. Then I pulled the oil plug and dumped it into my oil catch pan and on contact with a little water in the bottom of the catch pan it boiled it. Im glad I was wearing rubber gloves because some of that oil got on my finger.
So im thinking oil cooler with a thermostat?
The 18.5hp kohler V-twin has an oil filter and pumped oil system.
I was looking at replacement engines and they are over $1,000 so dont want to do that.
Anyone ever add an oil cooler to a riding lawn mower?
I have a transmission cooler that would be perfect, might add a fan but will try with out the fan. All I would have to buy is a sandwich adaptor and get some lines.
Mouse nest inside the fan area causing overheating? My friend blew a head gasket on an older Briggs single that way.

Edit:sorry just noticed everyone else already posted this. It is the most likely problem. I have an 81 Briggs 11 hp I was given and I remember it running extremely hot under normal use when the guy who gave it to me had it....sure enough it was full of mouse nests.
 

JRed

Site Donor 2021
Joined
Jun 1, 2009
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2,590
Location
Virginia
The Kohler on my Scag has an oil cooler that is part of the oil filter adapter and the finned portion tucks up inside the fan shroud. Same for one of my generators. That being said I don't think an 18.5hp motor on a 42" deck should need an oil cooler unless you're making hay with the thing.
 

oil pan 4

Thread starter
Joined
Feb 24, 2005
Messages
304
Location
eastern NewMexico
About once a week I blast out everywhere I can with compressed air. It stays pretty clean. Any thing that does get in gets chopped up by the fan.
It does burn about a quart of oil between changes.
I am cutting knee high tumble weeds.
A little bit less invasive thing I could try is put a 12 inch fan fan on the hood and force more air over the engine and in the engine bay. Might try that first. I have a fan laying around, fuses, breakers, switches, wire in my junk collection. I guess if the magneto can keep up with the fan it could work.
 

JTK

Joined
Aug 14, 2003
Messages
13,869
Location
Buffalo, NY
Yeah, I believe there were some Kohler commands and Kawasakis that came OEM with oil coolers.

After every mow I blow my OPE off with a leaf blower or compressed air. Like said, dirt and oil will still build up over time. Do that, keep up on oil changes, run fresh fuel and don't store the thing out in the elements and it's doubtful the engine will die just because the oil runs hot.

I like to use 15w40 if the OPE is used heavily, but in reality a 5 or 10w30 would still suit my climate fine.
 
Joined
Sep 7, 2020
Messages
353
Location
Ontario,Canada
As others have said, I think if u pop fan cover off, you will find crap in the fins. Mine runs cool enough I can hold my hand on the oil filter after 2 hrs.
 
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