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Kohler 20RZ surge/hunts at startup

Zephyr7

Active member
Just to update this thread for the archives:

I noticed this past Friday that my genset was running rough after startup. It was around 54*F out, which I thought was warm enough for the genset to be ok but apparently not.

I bought a new block heater a few weeks ago and just needed to install it, but thought I could wait for colder weather and be ok as I’ve been busy. Anyway, I installed it yesterday and today the genset started up and ran smooth no problem! It was about 60*F outside for my test.

I’ll update the thread again when it gets down into the 40s in the next month or so, but I’m pretty sure the block heater solved the problem with the unit running rough. This means thinner oil might also fix a problem like this, but I want to stick with the 10W-40 I’ve been using for over a decade.

BTW, this is an “on at 80 / off at 100F” block heater. There is no need for the 100/120 that the genset shops with. The lower temp block heater is fine with gaseous fueled generators, and it’s cheaper to run.

Bill
 

Birken Vogt

Email NOT Working
Here in California lots of customers use no heaters and I have never had one of these engines run anything other than perfectly clean even from below freezing. I suggest you may still be masking a problem here.

In fact I have not seen any gaseous set run any differently stone cold to warmed up.
 

Zephyr7

Active member
Any idea what the warmer block might be masking? The only thing I can think of is oil flow in the hydraulic lifters. I wouldn’t expect a “real” timing problem to be minor enough that just warming up would fix it.

Bill
 

LWB250

Active member
You're still on the ragged edge of gas pressure if you're only running 6" of water column. The spec is 7"-11". This will be most noticeable when the engine is cold and/or under heavy (block) load.
 

Zephyr7

Active member
Yeah, low gas pressure might well be part of it, if a cold block makes that issue worse. I do need to get that gas meter upgraded but they want something like $1,400 so I’ve been putting it off.

I have most of the parts (just need to fab an enclosure) for a 10kw load bank. I should build that and see if the problem occurs under load just like when it’s cold. Right now, I rarely have more over maybe 20% load on the unit.

Bill
 

LWB250

Active member
Yeah, low gas pressure might well be part of it, if a cold block makes that issue worse. I do need to get that gas meter upgraded but they want something like $1,400 so I’ve been putting it off.

I have most of the parts (just need to fab an enclosure) for a 10kw load bank. I should build that and see if the problem occurs under load just like when it’s cold. Right now, I rarely have more over maybe 20% load on the unit.

Bill
Why would you have to pay for a larger gas meter? Every utility I've ever had gladly installed a larger meter at no cost - after all, they're going to sell more gas! I always supplied the primary regulator, but they would upgrade or install a meter based on what I told them my consumption would be.

You do have to be careful as many residential gas utilities don't understand motor fuel applications, so be sure to have the fuel consumption specifications on hand for their review.

They also won't often understand the higher pressure requirements, so be sure they do and that any regulator for your residential equipment such as furnaces or hot water heaters is adjusted and sized properly.
 

Zephyr7

Active member
They say generators don’t use enough gas for them to cover their meter costs, so they charge for service upgrades for generators. My guess is if this was a brand new gas hookup, it wouldn’t matter, but mine is a capacity upgrade just for the generator.

They have no problem for 11” WC elevated pressure though. Regular gas appliances are ok with 11” because they have to be able to handle propane pressures too, just in case. I found that out from one of my mechanical contractors at work and confirmed it with one of the gas company engineering guys. If you want 2PSI or higher, then they want a licensed mechanical contractor to sign off before they do the upgrade.

The heat treating place I’ve been contracted to a few times over the past month or two runs 15PSI gas. Lots of Big furnaces. It’s a neat place. If you drive a GM vehicle, or a Ford pickup, they were the ones that heat treated your brake rotors.

Bill
 

LWB250

Active member
They say generators don’t use enough gas for them to cover their meter costs, so they charge for service upgrades for generators. My guess is if this was a brand new gas hookup, it wouldn’t matter, but mine is a capacity upgrade just for the generator.

They have no problem for 11” WC elevated pressure though. Regular gas appliances are ok with 11” because they have to be able to handle propane pressures too, just in case. I found that out from one of my mechanical contractors at work and confirmed it with one of the gas company engineering guys. If you want 2PSI or higher, then they want a licensed mechanical contractor to sign off before they do the upgrade.

The heat treating place I’ve been contracted to a few times over the past month or two runs 15PSI gas. Lots of Big furnaces. It’s a neat place. If you drive a GM vehicle, or a Ford pickup, they were the ones that heat treated your brake rotors.

Bill
Interesting. I've never experienced that from a residential utility.
Odd.

You want big gas? Try Kohler as the largest consumer of liquid propane in the nation at one point. Before they had a high pressure natural gas pipeline run to the plant, they used propane to fire the four city block long kilns in the pottery. These are so big you can literally drive a car through them. It takes over a week to fire one and bring it up to temperature, and because there's often damage to the lining from thermal stresses, they don't turn them off or let them cool down - even during plant shutdowns. They load the kiln cars with brick and run them through so there's always a load.
 

Zephyr7

Active member
Those must be some big kilns. That would be interesting to see. Kohler keeps wanting to fly me out to their factory for a tour (and sales pitch stuff I’m sure :), maybe I can see more than just the Kohler power stuff... then again maybe not, I jokingly asked if they could throw in a free toilet or faucet or something. With a high 6 figure generator order and they told me that the power division is totally prohibited from ordering anything from the plumbing division.

Bill
 

LWB250

Active member
Those must be some big kilns. That would be interesting to see. Kohler keeps wanting to fly me out to their factory for a tour (and sales pitch stuff I’m sure :), maybe I can see more than just the Kohler power stuff... then again maybe not, I jokingly asked if they could throw in a free toilet or faucet or something. With a high 6 figure generator order and they told me that the power division is totally prohibited from ordering anything from the plumbing division.

Bill
The various divisions are totally separate in the corporate structure, there’s no mechanism for internal transactions outside of each division. Power Systems is a completely separate company as is Plumbing and Hospitality. That being said, you can be sure all of the plumbing products in our buildings were Kohler...

The Generator Division never had (public) tours as long as I worked there, mainly because the production floor is quite “open” in that people could be walking around and see things they shouldn’t, like development products that haven’t come to market. I would take my classes out there, but it was scheduled in advance so that things could be covered or put away if necessary. The guys on the production floor always enjoyed talking with my people and showing them how they put the product together.

The best thing to see, and one I always took my students on when they came up for training, was the main plant tour. It takes about 2-3 hours and goes through the pottery, brass and foundry. They leave from the Design Center daily in the mornings during the week. Very impressive. You get to walk out on the factory floors and see them pouring molds for pottery in the morning, walk by the kilns and see the kiln cars being loaded with green ware being readied for firing, the brass shop where they're plating and polishing, and my personal favorites, the foundry and enamel shop.

The foundry has an automated production line (the “Herman Line”) where a tub is poured every 20-30 seconds or so. In the enamel shop you can see the enamelers enameling tubs by hand, some of the highest paid hourly employees in the company. It’s really amazing to see and I never tired of going on that tour.

Dan
 
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dkamp

eMail NOT Working
I'm goin' with the likelyhood amalgation of Bill and Dan's suggestions:

Cold oil.

Low or unstable gas pressure.

And I'll add one more thing:
Intake ice altering the ID of your venturi.

Now, your observations are clear, predictable, and repeatable... so now is the time to change something, and see if the observations you've had, stay same, or change.

I would replace the oil with a different weight, for a TEST.

It very well may be that the issue is insufficient fuel flow... going to a lower viscocity oil may reduce the amount of running load when warming up, to reduce the fuel demand of the engine, and realize that it takes additional fuel to WARM the engine just simply because it's parts are absorbing waste heat rapidly, and their running dimensions are changing.

If you're seeing a 7" fuel gas pressure, when the demand reg is designed for 11", then you're gonna have problems... you're well outside a 10% tolerance of expected pressure.

Realize that the demand regulator is about the closest thing to a precision measuring instrument that exists in the entire control system of your generator, and it's analog, and mechanical. The surface area of it's diaphram is performing a differential pressure calculation, and yielding a perfect balance between spring force, and valve opening force, through a known orfice, modulated by a precision taper...

like any other computing device, the demand regulator is a garbage-in/garbage out device. If your gas pressure is too low, or unstable, or flow is restricted, FIX IT... there's no way around it.

Oh, and one other thing to be aware of... natural gas lines are subject to impurities of both solid and gaseous personality. When someone works on a natural gas line somewhere between you and a source, a certain amount of 'unnatural gas' appears... like... atmosphere. Anytime there's a problem with a booster pump, they flip some valves to bypass the booster, work on the booster, then flip the valves back, a certain amount of air winds up IN that line, and gets pumped downstream to customers.

At the customer's end, it's frequently unnoticed... mebbie the furnace takes a big bubble and flames out, so it goes into a restart. mebbie the pilot light of your water heater blows out... or the stove hast'a snap snap snap a few times for a restart.

Some customers, because of plumbing circumstances, wind up being the 'settling point' for all non-expected air bubbles... and when this happens, THEY get to be the solution... the place that becomes the 'trap' for the worst of the air bubbles.

IF your feeder is the most likely recipient of air-bubbles, and your line doesn't have other really-substantial-loads, you get to be the person who keeps the line clean for everyone else.

Try thinner oil, get that gas pressure back up where it belongs, and make sure your gas feeder has a proper drop leg or two, and 'chat up' your local gas technician, perhaps they'll let you in on local gas issues that may be complicating your service quality a little.

Emergency generators, like anything else that's considered 'critica', should NOT be kludged. Putting a block, oil-pan, or battery heater on a generator isn't a bad thing, but it should NOT be the solution for some other problem elsewhere. My generators, from 5kw up, all hand-start on propane at -25F, and those tanks develop almost no tank pressure, and it's important that I can do that, because when I need emergency power the most, conditions are usually just that bad... typically, -20F, high winds, ice tearing down utility lines, and the road is 6ft drifted shut with zero visibility. Having to rely on something like an engine heater is a huge weakness. It should be able to fire right up cold, and even if it's a little rough while warming, it should be ready and smooth within 4-5 minutes.

Intake ice on the venturi is a function of temperature and humidity... it can happen at basically any temperature, so if your throttle body doesn't have an exhaust or coolant temp line running through it, you're susceptible. An IR thermometer pointed at it, measured before starting, then take regular measurements every 15 seconds for 10 minutes, and write them down, you'll have an excellent idea of what's happening there. ONLY solution to throttle body ice is adding heat upon startup. A generator can do it with electricity, a resistive heat plate, and a water temp switch... as soon as engine starts, it gets warm, once engine coolant is up to temp, it turns off.
 

Zephyr7

Active member
I’m at the very end of my gas line in the street, their last customer. I know this after asking the gas co engineer I was talking to about upgrading the service. I do need to get that meter upgrade done, I’ve been putting it off because I don’t want to spend the money.

Throttle body on this engine is a pretty heavy casting basically bolted right to the block. It stays at or very near the temperature of the outside of the block, so I’m not worried about icing.

I agree using a thinner oil would be a good way to determine if too-thick oil is the actual issue here. I might try that when the weather gets colder so I can do some consistent tests, but I’d swap it right back after for the heavier oil. It would be some generator maintenance in cold weather which I try to avoid, but I would like to narrow down the possible causes of the issue.

No drip let near the unit, they are not suppose to be used in outsoor lines here due to the risk of freezing and potential rupture if they have any water in them. There is a drip leg about 15 feet of pipe away inside the house though, and the pipe transitions vertically for about 10” on the way to the generator inlet connection. We’re probably not seeing an issue with particulates coming down the gas line.

Gas pressure is low but stable as measured with my manometer. It’s also possible that the real “problem” is a combination of thick oil when cold AND low gas pressure. I do know the gas pressure is about the same and just as stable in cold or warm weather since that I have checked.

Bill
 

dkamp

eMail NOT Working
...Throttle body on this engine is a pretty heavy casting basically bolted right to the block. It stays at or very near the temperature of the outside of the block, so I’m not worried about icing.

...Gas pressure is low but stable as measured with my manometer. It’s also possible that the real “problem” is a combination of thick oil when cold AND low gas pressure. I do know the gas pressure is about the same and just as stable in cold or warm weather since that I have checked.
Doesn't matter where the throttle body is bolted... when air flows through a venturi, the pressure drop at the divergent zone is low enough to form ice, and narrow the venturi enough to change the demand regulator's draw pressure.

Carb/Throttle body icing occurs as a result of Combined Gas Law (Boyle's Law being a subset), where pressure, volume, and temperature are all proportional. It is the same circumstance that yields heat in compression, and refrigeration in an air-conditioner... it is a law of nature and physics, and there's no place you can put something that's being cooled that will stop it from happening... it take lots of heat to keep atmospheric moisture from condensing and freezing. This is one of the biggest reasons small aircraft crash within a mile of the departure runway.

My 17 boat has a GM inline six... a wheezy old 1973 250ci, with 307 flattop pistons at 10.75:1 compression ratio, .512 lift cam and throttle body injection on a raw-water cooled combination intake/exhaust manifold. On an average boating day with 80F water, on an 85F day, the throttle body ices for the first 2-4 minutes of running time, and there's no way to generate enough carb-base heat to prevent it... until the manifold is at 140F, it's gonna have ice in it.

My '57 Allis Chalmers D17 does it on a 90F summer day. My Kohler L600, and the 338ci Hercules JXLD on my big Kato ices too. All three of these engines have something common to industrial engines- where the exhaust manifold and intake manifold meet, is a common part of the cast-iron... so that exhaust heat on one side, is up against the intake about an inch and a half from the carb base and throttle plate.

It's not a matter of wether it happens, it's a matter of wether it causes an immediate problem... which includes:

1) CRITICAL restriction of the inlet flow... this is the part that drops aircraft- they're operating under full power, and ice building up inside the venturi rapidly accumulates such that the ID of the venturi closes, pushing the divergent zone towards the throttle plate, and reducing the amount of flow through. This causes airflow in the venturi to increase, which increases the chilling, and forcing the icing to propgate downstream. The result is like getting an extreme allergy or asthma attack- the airway constricts.

2) Jamming of the throttle plate. Engine won't govern, and usually, it can't be throttled back to reduce icing.

3) change of fuel demand signal - since the venturi ID and shape are changing (the divergent zone moving away from the main jet or spud) the fuel pressure signal at the spud changes substantially. Depending on geometry, that signal will go way up (forcing a richer mixture) or way down (going lean).

So don't believe that it isn't happening... it ALWAYS does... the only difference is wether it's causing a problem. When we start machines and allow them to idle, they generate heat from combustion, and from friction, which thins out the oil, and brings everything gradually up to the normal operating zone. Generators have a tough time with this, because they don't low-idle... they 'high idle', which is to say, they're running at full operating crankshaft speed... but with no load. It's not a great way to start a cold machine's day, but this is the fact of a backup generator's life... and it's not just limited to oil, critical dimensions, and carb ice... even the temperature of the generator head causes enough change to result in voltage being a little different. Good design mitigates, but cannot eliminate these warmup instabilities.

The fact that your gas pressure is low, but STABLE under load change, supports the conclusion that you don't have any critical restriction circumstances... but being that low, I think you're getting too low for the fuel controller to accurately meter based on demand pressure.

I think you have THREE circumstances...
thick oil = greater crankshaft load,
low fuel pressure = ineffective fuel metering,
and venturi icing displacing the fuel demand signal slightly off the demand regulator's proper operating curve.
 

toddbailey

New member
I have a similar issue. I recently replaced the coleman barber with one from GAC, there model ecg6500. setup was pretty easy but about best speed regulation (i can get) is from 1785 to 1810 rpm in a slow peridoc eg: about 1
-2 seconds.

what controller are you using? I found and downloaded manuals for the coleman and gac that I can share if you want.
 
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