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Oil consumption and running a diesel hard enough

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
As a relative novice, this thread is very informative. I do not have a temperature gauge to read actual temp of the diesel. I do take readings, mostly out of curiosity only, with a handheld infrared thermometer taking reading at various spots on the engine. The readings are never high enough to cause alarm. Higher in some spots lower in others. Where is the most reliable place(s) to take these readings on the engine?

I like to point it at the exhaust manifold, and at the elbow where the water is injected. I do not know enough to be dangerous, but it's interesting to see the temp. drop where the mixture goes into the exhaust hose. And then there is the engine head, and sometimes the transmission when under load. And also the metal pipe takeoff for the hose run to the hot water tank.
If you have a Ship's Cat, he/she could chase the pointer for fun, too! :)
 
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Kenneth K

1985 32-3, Puget Sound
Blogs Author
Does anyone know the Universal, or better yet the Kubota part number for a 180 degree thermostat for an M25?
 

Geoff W.

Makes Up For It With Enthusiasm
Blogs Author
Bookmark this:

http://www.c34.org/wiki/index.php?title=Diesel_Engine

Engine Thermostats
M-25/XP/XPA; 35/A; early M-25XPB (to March 1998) use these 38mm diameter thermostats:
160* F - Universal p/n 301358 or Kubota p/n 1E399-73010 (replaces 19203-73014, 19203-73013, 19203-73010.)

180* F - Kubota p/n 15531-73014 (replaces 15531-73013, 15531-73011.)

38mm Gasket - Universal p/n or Kubota p/n 16851-73270 (replaces 15676-73270, 15531-73270, 15676-73272.)

Later M25-XPBs (after March 1998)

44mm 160* F thermostat Universal p/n 201001 or Kubota p/n 19434-73014 (replaces 19434-73010, 19434-73013)

44mm Gasket - Universal p/n 298843 or Kubota p/n ?

See Service Bulletin #107, Kubota Tstats likely won’t have a bypass hole, so drill a 1/8” hole, or two, thru the inside edge of its flange so there is a constant coolant flow thru the exhaust manifold when the Tstat is closed.
 
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bgary

Advanced Beginner
Blogs Author
Nice!

From my hoarded PDFs, the Universal PN for the thermostat is 301358, which maps to Kubota PN 15531-73010... but both of those are for the 160F version.

Note that those part-numbers are for the thermostat, not the housing, the gasket, etc.

Bruce
 

markvone

Sustaining Member
44mm Thermostat Info - 180F

My 1981 E36RH has the Universal 5424 3 cylinder diesel which predates the M-25. The manual clearly states the operating temperature range is 175 - 190 degrees F and in another location, 80 degrees C (176F). It has a 44mm thermostat, Universal p/n 299798, which is a 160F. Cost is $30 +/-. It is dumb to use a 160F thermostat in this engine.

My Kubota tractor was the L245LT and the engine a D1100 series 3 cylinder. The Kubota thermostat p/n is currently 1E401-73010 ($30 +/-) which is most likely a 180F, but I have not been able to confirm. However, I'm positive Kubota does not make their own thermostats. Stant makes lots of OE thermostats. If you check your Kubota info in the below link you will get the Stant p/n 13848 44mm, 180 degree thermostat. It looks like this model fits almost all Kubota models that use a 44mm thermostat. Currently on sale at Amazon (Prime) for $5.35. You will have to drill two 1/8 inch bypass holes in the flange per Universal Service Bulletin #107, which you will need for the Kubota part as well.
Happy motoring at 180F after that.

https://partcat.com/stant

For the 38mm thermostat. I would check other OE thermostat mfgs (Gates, AC Delco, Motorad)

The tractor info for the M-25 variants is the B1750 series and the D850/950 engine. Stant doesn't have a 38mm thermostat for the earlier (pre 1998) Kubotas.

I'll post a picture of the two when I get home.

Mark
 

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debonAir

Member III
Hmm, AFAICT

The Kubota part 15321-73015 as in the L245 parts catalog (see Messicks). That is a 180 degree thermostat and is what came with the tractor from the factory
The Kubota part 19434-73014 (and -73010 and -73013 it seems), which is also Universal part 299798, is the 160 degree unit and is what came with the boat from the factory

I've read, but don't quite believe, the lower temperature was chosen to avoid salt precipitation in the heat exchanger. The sea-water temp in the exchanger doesn't really get that hot, as long as its working ok. I've also read that sea-water cooled engines can get salt precipitation issues which is more plausible since there are real hot-spots inside the block where water can get past the atmospheric boiling point and is why the system is pressurized. Of course, if I take a pot of ocean water and boil it on the stove I don't get salt coming out unless I boil it almost all the way down, so there's that. Maybe the marine diesel makers just always bought 160 degree units since they had salt and fresh water cooled engines?

A bunch of folks use the 180, especially fresh water cooled folks. I'm on the fence, and am days away from replacing my own with the 160 replacement I got. I'm stopping at the Kubota dealer this week to hopefully borrow the special 43mm socket to get the crankshaft nut off. I'll ask them their opinion. People seem to say the 180 gives a better running, cleaner, more efficient engine which is also what theory says, so I could easily be swayed. Plus I could probably take a little longer shower with the slightly hotter tank :)

Note also that super cheap thermostat deals often don't include the gasket which ought to be replaced when you have the housing apart. Make sure you're comparing apples to thermostats.
 

bgary

Advanced Beginner
Blogs Author
My two stupid questions for the day

-- "should" I change to a 180F thermostat? On the one hand, it seems like it should be healthier for the engine, long-term (especially as mine seems to be running even lower than 160F these days)? Or.... is there something to be said for "if it ain't broke, don't fix it"?

-- If I do change the thermostat.... do I need to drain (and replace) the coolant to do the job, or drain just enough to be below the level of the thermostat and then top-off and bleed, or...? What's the recommended best-practice? (coolant was flushed/replaced in August 2017, about 60 engine-hours ago).

Bruce
 

mfield

Member III
"should" I change to a 180F thermostat?

My understanding is that a 160 thermostat will start to open at 160 but will not be fully open until 15 degrees higher. This would put you at a near optimal range with the thermostat fully open. To go to a higher temperature thermostat would risk operating at the top end of the range (170-190).

As the thermostat opens at 160 you will have to wait a little longer at a suboptimal range for the engine to warm up but I would rather err on the low than the high side.
 
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markvone

Sustaining Member
My two stupid questions for the day

-- "should" I change to a 180F thermostat? On the one hand, it seems like it should be healthier for the engine, long-term (especially as mine seems to be running even lower than 160F these days)? Or.... is there something to be said for "if it ain't broke, don't fix it"?

-- If I do change the thermostat.... do I need to drain (and replace) the coolant to do the job, or drain just enough to be below the level of the thermostat and then top-off and bleed, or...? What's the recommended best-practice? (coolant was flushed/replaced in August 2017, about 60 engine-hours ago).

Bruce

Bruce,

You need to find out why you are running colder than the 160F setting first. This just makes the light load/low temp running diesel issue worse. I have the same problem. I verify temperature with an IR thermometer gun at the thermostat housing and exhaust manifold at a max of 145F. The seawater temperature doesn't matter, nor does the HE size - unless the thermostat has failed open. I have seen car thermostats fail open where the frame broke. You can also have debris hold the stat open but this seems unlikely with fresh coolant. I would check your thermostat first.

I would certainly change to the 180F if you have it out. On the 5424, the thermostat housing is at the top of the engine on the front. A towel wrapped around the stat and the fill cap on the exhaust manifold will collect the ounce or two of leaked coolant. Remember to plug any overflow/expansion hoses that go up above the engine to expansion/overflow tanks. You shouldn't need to drain the entire system unless the stat is the lowest point on the M-25.

In my experience, the better the cooling available (lower seawater temp and 3 inch HE size) the closer the engine will operate to the thermostat setting. Once the stat is partially open and sending coolant to the HE, the coolant temperature will stabilize somewhat above but near the stat setting. I would rather run a diesel at the high end of the 175 - 190F range as long as I'm consistent and not overheating.

My original thermostat (Universal 160F in the picture) was fine. I think my issue is that I'm not loading up the engine enough to generate heat. In my case, I'm not getting past 1700 rpm underway at max throttle. I can get 3000 rpm in neutral (verified with optical tach). I used to get 2800 rpm/7.2 knots max. I've lost cruising rpms over some period and the boat certainly doesn't have the get up and go it has had in the past. I don't generally motor very far or often and my creek speed limit is low so I didn't notice the lost rpms until I motored 12 miles to and from a marina for my first ever winter haul out with this boat. I had the same limited rpms both ways but much better speed in the spring with a clean bottom (6 mph vs 4.4).

A test this week confirmed my lost top end rpms.

Mark
 

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debonAir

Member III
Hi Mark, I am guessing you meant you get 3000 rpm in neutral, not "idle". The 2800 -> 1700 is a really significant drop. I notice my speed being significantly slower on the way to Winter storage in the fall vs. on the way to the mooring in the Spring. I attribute that to bottom growth and slime (but enthusiasm could be a factor) but both ways the engine is running at the same 1800 rpm cruise. I don't think I could even get to 2800 WOT in gear, maybe with an empty boat and clean bottom. What kind of prop do you have? Have you tried sea-foam or STP diesel treatment? I usually don't ever consider "magic fluid" type fixes but I have heard of people getting good results from both of those treatments.
 

bgary

Advanced Beginner
Blogs Author
.... I verify temperature with an IR thermometer gun at the thermostat housing and exhaust manifold at a max of 145F.

I don't know how accurate the temp gauge is.

I have verified temperature with an IR thermometer, both at the exhaust manifold and at the thermostat housing. Both consistently read 145F

So now I'm (more) confused... does 145F at the exhaust manifold indicate that it is really running at 160F and the temp gauge is wrong?

Bruce
 

markvone

Sustaining Member
Bruce,

My temp gauge sender is in the thermostat housing cap (the black cylinder in the pic in post #30). My IR temp readings are 145F on the housing but the gauge is barely off the 120F peg, so my sender or maybe gauge cal (if there is one)is slightly off. I have a new gauge in the panel and the old sender so I need to check compatibility. My exhaust manifold temp is the same as my stat housing. You are running at 145F. You should be 160F - 170F with the 160 thermostat functioning normally. Your engine will generate heat up to 160F when the thermostat opens and starts to cool the coolant. The temp should stabilize somewhere just above 160.

debonair,

My prop is a folding Martec 18D x 12 pitch. Thanks for the suggestion for injector cleaner. I'll try that first. I also need to investigate the exhaust elbow and muffler/hose for a restriction. I have less than 200 hours on the engine in the past 8 years so I don't think it has gone south in the last couple of years. I still suspect a fuel restriction. I cleaned my fuel tank a couple of years ago and don't have many hours on the filters but I need to re-check the fuel supply to find those lost rpms!

Mark
 

bgary

Advanced Beginner
Blogs Author
My IR temp readings are 145F on the housing but the gauge is barely off the 120F peg, so my sender or maybe gauge cal (if there is one)is slightly off.

I guess I bungled my question.

When your IR temp readings at the thermostat housing are 145F, does that mean your engine is running at 145F, or is there some factor that means "when temp at the housing is 145F, it means the engine is running at the proper 160F"?

Bruce
 

markvone

Sustaining Member
Bruce,

The coolant temp is the running temp and the temp sender should be sending that temp to the gauge. The metal parts of the engine (block and heads, manifolds) transfer heat very well to the coolant so most of the exterior metal engine parts are pretty close to the coolant temp.

When I'm measuring the thermostat housing at 145F with the IR gun, that's pretty much the coolant temp and the engine is considered running at 145F.

Mark
 

bgary

Advanced Beginner
Blogs Author
Ordered a 160F thermostat from the local Kubota dealer. Not sure if it will be in by the weekend or not, but hopeful that it is an easy change that doesn't break anything on a motor that's been running just great.

Quick Q: I ordered the gasket, too, and am wondering whether the paper gasket by itself is enough, or if gasket compound is also called for? when I replaced the coolant pump, I used high-temp-compatible "water-pump" gasket compound on both sides of the paper gasket....

Bruce
 

Frank Langer

1984 Ericson 30+, Nanaimo, BC
Hi Bruce,

I also used a gasket sealant product when I replaced my fresh water pump, but have always only used a gasket on the thermostat, and never a leak there. I think as long as the previous gasket is totally removed and the surfaces are clean, the gasket alone should be fine. In the unlikely case that it does leak, it wouldn't be difficult to add some sealant, but it shouldn't be necessary.

Frank
 

markvone

Sustaining Member
I only use the paper gasket. Which is only $1.10 from Universal, Kubota may be even less.

FWIW, I reused the paper gasket which was completely intact and un-stuck from both surfaces when I had the thermostat housing open a few weeks ago for the previous picture.

Mark
 

Geoff W.

Makes Up For It With Enthusiasm
Blogs Author
@Bruce Where did you order the part from? I went off an online store.

I also got a new 160F thermostat and gasket / gasket cover in -- but the paper gasket is just a square, no special shape. Do I need to cut it to spec myself, or is there something I'm missing?
 

debonAir

Member III
Ordered a 160F thermostat from the local Kubota dealer. Not sure if it will be in by the weekend or not, but hopeful that it is an easy change that doesn't break anything on a motor that's been running just great.

Quick Q: I ordered the gasket, too, and am wondering whether the paper gasket by itself is enough, or if gasket compound is also called for? when I replaced the coolant pump, I used high-temp-compatible "water-pump" gasket compound on both sides of the paper gasket....

Bruce

According to Kubota manuals, the gasket itself and no sealant are sufficient. For all their gaskets. Personally I don't think that's really true when you're putting back on an old corroded part that you had to scrape the old gasket off of and there's residue. I plan on a thin coating of black RTV on the cover-side of the gasket when I put my timing gear cover back on. The block side is nice and smooth still, so will leave that alone.

IMPORTANT: As mentioned earlier in this thread, there is a difference between off-the-shelf Kubota-dealer thermostats and the ones in the Universal engines: The Universal t-stats have two (what I've seen) small (1/8") holes drilled on the outer rim/lip. These holes let some coolant flow even when the engine is cold. This is to provide some cooling flow into the exhaust manifold which heats up much faster than the block. You can easily drill these yourself in the Kubota t-stat. There
are pics somewhere of how the holes look, or use an old Universal one as a template.
 
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