MEP803A Thermostat

Zed254

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My MEP803A (2012 Letterkenny Reset with 53 hrs) overheated and shut down during a 105% PF run a few weeks ago so I changed out the thermostat. I bought a new Onan Thermostat on the auction site with the correct NSN # (6685-01-360-9653) and part # (186-6193). It is rated at 74C (165F). All good until I notice the one I pulled out of the generator was rated at 88C (190F). I ran it yesterday for several hours and the Temp gauge never got over 175F at 105%PF. I ran at 113%PF for around 40 minutes until it tripped out on overload - still 175F temperature. I reset and continued to run at 105% to the end of the 3.5 hour run. The manual says normal run temp is between 170-200F. As I was idling down at end of run the temperature dipped to 160F. Ambient temperature during run was 42 - 49F. Have I created a problem with this 74C thermostat and if not does anyone know why Letterkenny installed an 88C Tstat? I'm wondering if I should attempt to find one rated at 80C. Thanks.
 

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jamawieb

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I've run into this also, I've had several units that had the 190F thermostat's and just couldn't cool down fast enough before the over temp fault would activate. Most have the 165F in them now. Interesting fact but a standard Chevrolet thermostat is an exact fit for these units, also the gasket for a Chevrolet will work, with just a little trimming. The thing to remember is that a diesel needs heat to be efficient, I believe most of the these units never reach full load so the military used higher temperature thermostats to reduce wet stacking. Just my 2 cents.
 

Guyfang

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I went to APD, (Army publishing Directorate) and made sure we are still using the latest Generator parts manual. And indeed, the 30 October, 1996 Parts manual is still whats being used, and the numbers are still good. I looked at an old copy of FEDLOG. This doesn't mean the part hasnt be superseded, in the current FEDLOG. Would be nice to know. Sure wish we could get a copy.

So, I asked someone in the know, about there being an "improvement" to the engine coolant system. He told me no. Nothing. He did say that sometimes, when sets were reset, the agency performing the reset, had the latitude to use a part VERY similar, to the one needed, when the required part was not in the supply system.

How could it be that a part like the thermostat not be available? Well, the supply system can work like this. There may be, lets say ten thermostats in the supply system, spread throughout the the world. A certain amount of parts can not be shipped to a facility like reset, due to mission requirements, like our troops down range. The parts are there, but you cant have them. Your mission priority isn't high enough. So, someone like Reset, could get said parts by local purchase. It not an uncommon way to do things. And if getting the original part cant be procured, another VERY SIMILAR part can be substituted. This could also have happened. It could also be that someone said, "Hel*, its close" and used it.

Folks, you can use APD, if you want to see what the current manual is, what date it has, how many changes it has, and last but not least, if you're authorized to have it. Very handy. People on active, (or otherwise authorized) can access the site and download publications.
 
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Daybreak

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Howdy,
I do know the ambient air temp will make running temp different. I have run the same loads during summer with it being 92 degrees out and things were all higher. Below are some testing logs with ambient temps during runs. Its still very much in ranged spec'd for the unit.

Acquired a Military surplus load bank
 

Dwnorton1

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I would suspect that they would put a lower range thermostat in a gen set destined for Iraq due to the fact of super high ambient temperatures. A higher range for a colder climate. From what I've read these units are most efficient at around 180- 190 degree range. So it would stand to reason a unit that resides in Arizona might be better suited to the 165 degree unit, where a unit in Maine might be suited for the 190 thermostat. You will be most efficient running around 180 degree sweet spot. We would change out thermostats on our big diesels for irrigation pumps between winter and summer for this very reason.

This is just my opinion, which with 50cents still won't buy you a cup of coffee.
 

Zed254

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I acquired the generator in a 12/7/16 auction, so most runs have been in cooler weather and water temps have stayed below 200F. On 3/1/17 the high ambient temp was 81F so ambient conditions definitely contributed to the 210F water temp and resulting high temp shutdown. I am a wee bit concerned about running in winter/cold ambient conditions with the newly installed 165F T-stat but will leave it as is during summer. I hope to find a 180F thermostat before winter in case I feel the need to warm it up. Thanks much for everyone's input.
 

Guyfang

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I would suspect that they would put a lower range thermostat in a gen set destined for Iraq due to the fact of super high ambient temperatures. A higher range for a colder climate. From what I've read these units are most efficient at around 180- 190 degree range. So it would stand to reason a unit that resides in Arizona might be better suited to the 165 degree unit, where a unit in Maine might be suited for the 190 thermostat. You will be most efficient running around 180 degree sweet spot. We would change out thermostats on our big diesels for irrigation pumps between winter and summer for this very reason.

This is just my opinion, which with 50cents still won't buy you a cup of coffee.
This is something the military would never do. The military is all about standardization. Equipment has to be able to be sent ANYWHERE on the face of the world, at any time. There are regulations against any kind of modification, of any kind. BUT, there is always the option to apply for an "Exception of Policy". so people who "NEED" to make a"Non Authorized Mod", can do so. But it has to be able to be reversible, without damaging the equipment. And there is some kind of time limit for how long you can take to do the reversal. The engineers sit down and figure out what the max range for ambient temperature the military might face, and plan from there. No, fiddling with all kinds of gear, in all kinds of units, in all kinds of environments, never happen.

Here is what a study of running gen sets in high temp areas found. I read this back in 2009, or 2010. Most units that over heated, were due to:

Dirty, grease coated radiators.
Incorrect, or no proper coolant.
Poor PMCS.
Dirty, grease coated engines.

And last but by far the biggest reason. Open doors. Open doors on the sets. The gen sets are designed to be operated with the doors, ALL doors, closed. When the door seals are missing, or not seated properly, bad news. And the number one reason? The door allowing access to the load terminals! Yep, that door. No one wanted to thread the cables into the sock, on the side of the gen set. Everyone opened the door, and hooked up the cables. There is even a PS magazine article on the "problem".
 

jamawieb

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Ok, the Chevrolet thermostat is a Murray Ultra 15358 and the gasket is a 2138. This Thermostat is 180F. Hope this helps!
 

Daybreak

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I acquired the generator in a 12/7/16 auction, so most runs have been in cooler weather and water temps have stayed below 200F. On 3/1/17 the high ambient temp was 81F so ambient conditions definitely contributed to the 210F water temp and resulting high temp shutdown. I am a wee bit concerned about running in winter/cold ambient conditions with the newly installed 165F T-stat but will leave it as is during summer. I hope to find a 180F thermostat before winter in case I feel the need to warm it up. Thanks much for everyone's input.
Howdy,
Besides what has been said. I would suggest you look into other issues with your generator. It should not matter that the thermostat was a 165 or a 190, it should not have shut down due to high temp.

IMHO, I would flush the radiator and engine block. I would look at the belt, the fan, and the radiator and fins. The cowling around the fan, and any obstructions. I would then fill the radiator with the proper coolant, run some, let cool, and top off coolant and ensure your recovery bottle has coolant to the proper level as well. Check you oil level too. I guess with you changing the thermostat, you have changed out the coolant already. Heavy duty diesel type coolant.
 

Zed254

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Could very well have been a problem with antifreeze mix: I was running on what was in it when I picked it up and never did check its ratio. It was clean, green (Guyfang's yellow bottle I suspect) ran well in the winter and so I ran it. Engine and radiator are clean and the fan belt is tight. I changed the oil to your recommended Deere break in oil at around 60 hours. I'm probably good to go, just suffering from the anal Engineer poking around my skull.....
 
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Zed254

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I've got a sticky coolant gauge and changed it out with......a 280F gauge. Did not work so well - always reading high. The sender in this unit is matched to that 240F Beede I took out so I jiggled around with it and re-installed it. I think it reads pretty accurately when it reads: was hitting 210F just before it overheated. I was in the house and was not there when it happened (and I'm trying to do better...) so I really don't know what it was reading when it tripped.

Does anyone know where I can get a floating ground sender for 280F or a replacement Beede coolant gauge? The sender that matches my 'new' gauge is a single pole sender.
 
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