Side mounted fire starter. Red Hot exhaust

[MossRoad]

On my 2001 PT425, with a stock Kohler muffler that exits out the rear of the machine, I've towed a fertilizer spreader that had a plastic handle. It was a good 20" back from the exhaust and it melted it right off, and warped the flow adjuster as well. Those little engines run extremely hot.

 

[MossRoad]

I've never had or even seen a PowerTrac, but as a mechanical engineer with a day job of dyno testing internal combustion engines, I will add my 2 cents.

That is not normal. Your exhaust gas temperatures are clearly way too hot, and that looks downright dangerous.

Sure, on a dyno torture test we can also get entire exhaust manifolds, turbos, and exhaust pipes glowing bright red here at work. But thats at sustained peak power conditions on highly boosted engines. A naturally aspirated Kohler 2-cylinder loafing around should not be anywhere near that hot. The only time I would call that acceptable is after a full hour of dragging a plow through soil on a hot summer day, or similar punishing work.

Multiple things can cause excessively hot exhaust gas temperatures. But ignition timing is an obvious suspect, valve timing another. Exhaust restriction would be also be one, but looks like you already answered that question. I know it would be obnoxiously loud, but did you try running with no muffler at all, just to see?

Right there is the issue. These engines are never loafing around. They are constantly under load pushing 3 hydraulic pumps. The pumps are mounted directly to the engine shaft(s). There's no turning them off.

The PT425, for example, has a variable volume pump that is always circulating oil for the charge pump, something like 2gpm. There's a MAIN PTO pump that's 8gpm @ 2500psi, and an AUX PTO pump that 4gpm @ 2500psi. Even at 1/3 throttle, just sitting there warming up in the winter, within 20-25 minutes, the 10 gallon hydraulic tank will get hot to the touch.

This is mine. It's a different setup than others, but you can see it's a factory muffler and exhaust manifold. You can't keep you hand behind the exhaust within 20" of it for very long.

 

[zzvyb6]

I'm betting that somebody 'turned up' the motor to get 'more power' and defeated the fuel settings to escape emissions rules. So now, a rich fuel ratio is indeed passing thru, burning i the exhaust manifold, increasing combustion temps, pumping out nitrogen oxide and providing that good old hand warmer feeling.

 

[joshlee]

This is a interesting thread I’m learning allot

 

[deezler]

Right there is the issue. These engines are never loafing around. They are constantly under load pushing 3 hydraulic pumps. The pumps are mounted directly to the engine shaft(s). There's no turning them off.

The PT425, for example, has a variable volume pump that is always circulating oil for the charge pump, something like 2gpm. There's a MAIN PTO pump that's 8gpm @ 2500psi, and an AUX PTO pump that 4gpm @ 2500psi. Even at 1/3 throttle, just sitting there warming up in the winter, within 20-25 minutes, the 10 gallon hydraulic tank will get hot to the touch.

Ok, but simply flowing hydraulic fluid shouldn't take that much power (fuel) if you aren't asking it to do any real work (no built pressure). Any tractor or hydraulic machine is constantly turning their hydraulic pumps also. And most of them don't need to have red-hot exhaust (even gasoline motors). If all the PT machines run like this, then I suppose it is normal, but strikes me as poor engineering. Is there some inherent hydraulic restriction that causes pressure to always be built? Do these PTs burn a crazy amount of gasoline as a result? If not, and the fuel consumption seems moderate and normal, then it's an engine tuning issue, IMO.

 

[Goose1776]

I'm betting that somebody 'turned up' the motor to get 'more power' and defeated the fuel settings to escape emissions rules. So now, a rich fuel ratio is indeed passing thru, burning i the exhaust manifold, increasing combustion temps, pumping out nitrogen oxide and providing that good old hand warmer feeling.

It’s a brand new machine. With a new engine from Kohler
Im not sure how someone would have adjusted anything on it

 

[MossRoad]

Ok, but simply flowing hydraulic fluid shouldn't take that much power (fuel) if you aren't asking it to do any real work (no built pressure). Any tractor or hydraulic machine is constantly turning their hydraulic pumps also. And most of them don't need to have red-hot exhaust (even gasoline motors). If all the PT machines run like this, then I suppose it is normal, but strikes me as poor engineering. Is there some inherent hydraulic restriction that causes pressure to always be built? Do these PTs burn a crazy amount of gasoline as a result? If not, and the fuel consumption seems moderate and normal, then it's an engine tuning issue, IMO.

It's running at 3600rpm. There's 4 hydraulic motors, one at each wheel. There's a hydraulic motor on the mower, brush cutter, etc.

Even without any attachments, there are restrictions in hoses, fittings, etc.

I'd bet that if you took any 2 cylinder twin engine and put an elbow on the exhaust pipe and ran it at 3600rpm without a load, that elbow would soon start to glow in the dark.

 

[ponytug]

I think @deezler's point about the hot exhaust being a sign of wasted energy is well taken, but I think it is in the nature of more recent air cooled gasoline engines that run toward hot exhausts as a side effect of meeting emissions requirements. This may be normal for PT-425, but that doesn't mean it is great. I suspect that non-factory exhausts don't help, as the factory exhaust systems are general "tuned" an optimal amount of back pressure to have the optimal amount of residual exhaust gases left in the cylinder for emissions management.

Absent significant fluid dynamics calculations and access to @deezler's dyno setup with emissions, I don't think that it is an easy fix.

While it doesn't address the energy or fuel consumption issues, if it were me, I would be tempted to put a secondary exhaust shield on just for fire and safety reasons.

Given @MossRoad's experience, perhaps PT-425s should be treated like horses? e.g. "Never stand directly behind one?"

All the best,

Peter

 

[joshlee]

The possible issue about the engine running too lean is an easy one to test, pull the spark plug out and see what color it is.

 

[MossRoad]

The possible issue about the engine running too lean is an easy one to test, pull the spark plug out and see what color it is.

It's white and says Acell.