MEP-803A Hard cold starting

Hi guys I'm new to the forum I picked up an 803a from guy ran great when I bought it. It was warmed up and running when I got there, little did I know that the thing will not start cold.
I have changed all the filters bled out fuel system, I have tried everything.
The only thing that helped was we changed to 10-30 oil in it now I can atleast get it to start but still hard. I had a friend tell me it may be a valve problem but I have been searching the sites and that doesn't seem to be an issue.
Any idea's you guys can give me would be much appreciated.
Thanks

Welcome to the forum!

Please explain your cold start up procedure.

Are you using the pre heat function? Are the heaters working?
Are you allowing it to prime up for 30 seconds to a minute or maybe two minutes?
Are your batteries up to snuff?
Can you see oil pressure building if cranking it for several seconds?

More info would help us all to point you in the right direction.

I am using the preheat function for about 30 seconds I did check the heater and the are working.
Batteries are brand new
Oil pressure is coming up
I may not have been let it prime for that long. I did not realize it had to prime
What happens is it will fire up for about 5 to 10 seconds and die. than if you try to restart you can't even get a puff of smoke.
The engine has a rebuild tag and has 900 hours on it.

Are you getting any fault lights?

Tear a small piece of paper off, and then pull the dipstick out while the gen set is running. Hold the paper in front of the dipstick hole. As close as you can get it. The engine is supposed to have a vacuum on the crankcase. So, that means the paper should be pulled toward the hole. If the paper flutters towards you, and not held down to the hole, you do not have a vacume. That can mean you have a problem. Perhaps you should read the -24 TM about what can cause that, IF you have pressure insted of vacuum.

No fault lights on

Are you turning S1 to the off position after it dies to reset everything? How long are you holding S1 in the start position? It may take several seconds for oil pressure to build in the cut off switch to keep it running.

Yes after it dies I turn it back to off position. Probably 10 to 15 seconds in start position after it tries to start. It does build oil pressure.

What happens if you hold it in the start position longer?

it still dies

try holding the fuel shutoff in the run position, then try and start. If it runs okay, then it's probably an electrical problem. If it still does not run, then you are probably getting air in the fuel system. I assume the electric fuel pump is running.

If you ever buy a diesel and the person has it running before you get there be cautious. People love ether to start diesels but ether destroys the cylinder walls and rings. It will cause lose of compression, making it very difficult to start, I think you need to go back to Guy's suggestion about vacuum and do his procedure. The other problem that comes to mind is the electric fuel pump, it could be going out and intermediately loosing pressure. I would take one or two of the hard lines off the injector pumps off and see if the pumps are working while cranking. If you see fuel coming out of the injector pump at all times then that would lead me back to compression. I know your Wisconsin but I have several units for sale on craigslist now, if you wanted to do some trading. I tinker with them as a hobby so I like new challenges.

We are thinking it is a valve issue. I have been threw the entire fuel system changed out fuel pump already.
The reason we are thinking valves is we changed out the oil in it that was thick as tar. To a 10 30 oil and with the lighter oil it started a lot easier. We are thinking the valves are not sealing with the thicker oil.
We can turn engine over by hand from the fan pretty easy. Is that normal?
What do you have for sale?

I've seen this a couple times when the weather gets cold.
Try putting a mechanical oil pressure gage in it. You need a gage with a 1/8" NPT thread. Screw it in in place of the original sender for the gage.
Start it up and check the oil pressure immediately. If the pressure goes too high ( above say 75 psi.) you are going to pump up the lifters and loose compression as soon as it starts.
I've seen this happen due to stuck and defective oil pressure relief valves.
Switching to lighter oil in cold weather might help, but you're just masking the problem.
I think the relief valve should keep pressure to under 60 psi. If you peg the gage up over 100 psi you have a stuck relief valve.

If the oil was thick as tar i would fill the thing right up to the top of the dip stick and let it soak. Then with the fuel off crank it over a few times. Then do a oil dump, fill, run and flush.

Never buy any engine thats warm and running when you get there.

How many volts are your batterys putting out?

The gauge on the front of the unit is over as far as it can go so this sounds like it could be my problem. Where is this relief valve located and can it be cleaned or does it need to be replaced.
Thanks for the help

If you start it and it quickly dies, then sounds like it has no compression when you try to restart it.... then you let it sit 1/2 hour and it has compression again.... that is the typical scenario when oil pressure goes too high and you hydrolock the lifters. This causes the valves to stay slightly open ( and often just touch the piston tops while cranking ) causing you to loose compression until the lifters can bleed back down again, usually 15 - 20 minutes.
If this is your situation you should remove the engine side cover and unscrew the relief valve, take it apart ( 1 snap ring ) and clean it and ensure the plunger is moving properly.
reinstall and refill with the proper weight oil. if you're in a real cold climate use 5-40 synthetic diesel oil, otherwise 15-40 is fine.

Once you get it running correctly you may want to inspect your pushrods. If you were in fact pumping up and hydrolocking the lifters, the valves will just about touch the pistons. It normally does not damage the valves because they hit perfectly flat, but you will quite often get a slight bend in some of your pushrods.

The relief valve is a 1" diameter tube about 6" long screwed into the back of the oil pump right next to the oil pump pickup tube.
Its all the way to the left looking into the open engine side cover, points down on a 45 degree angle almost touching the bottom of the crankcase.
Normally they can be cleaned easily, but once recently I had 1 that had a manufacturing defect and needed to be replaced. That particular machine always ran fine unless the temp went below 30F. as soon as it hit 30 degrees it was hit or miss if it would stay running. It had 140 psi of oil pressure on the mechanical gage at cold start with fresh 15W-40.
Replaced the relief valve ( because it showed no signs of being frozen and the relief openings looked much smaller than all the others I've seen ) started it up a 0 degrees F and it ran perfect and back down to 60 Psi cold.

This is why I love this forum^^^^^^^^^^^^^

Taking notes every step of the way.

When you take the side cover off is there a gasket that needs to be replaced? Thanks for the info sounds like relief valve is the problem. Do you know where to get a replacement one?
Thanks again