I have a recently-running 1999 Metro 6/1. It's hooked up to an ST-5 generator head. I'm using a thermo-siphon and 20 feet of baseboard heating cores as a cooling system. I have machined an adapter for an automotive thermostat (195 degrees) be be placed in the head to regulate temperature. The cylinder head heats to about 190 before the glycol starts flowing and holds a temperature between 193 and 205 for the entire time of the engine's running.

Here's the question: no matter what load I put on the engine, everything from idle to a continuous 3,500 watts being pushed by the generator, hours at a time, the water remains nearly constant in temperature, and heats quickly at initial startup because of the thermostat. I'm running just under a gallon of Rotella SAE30 oil in the sump. No matter the load, no matter the time the engine runs (often 8 hours or more at a time), the base of the crankcase never exceeds 130 degrees, which tells me that the oil never exceeds 130 degrees. It takes quite a wile (well over an hour of hard running) to attain this temperature.

I've always done well by the rule of never starting an internal combustion engine unless I plan on getting the oil good and hot to drive out the moisture byproducts of combustion, and in my mind, that means getting the oil above 212 degrees for a reasonable length of time. In this engine, however, that does not seem possible, and concerns me about the oil life and the buildup of acids and other unwanted chemistry.

A secondary question with this is that if the sump always stays relatively cool, should I consider putting a 15 weight oil, or a multi-viscosity oil (15W-40?) for winter? It's not uncommon for me to want to run this engine at temperatures well below freezing, and since the sump never gets hot, I'm seriously wondering about the effective splashing action of honey-thick oil in there.

What has experience taught all of you who have had their engines run far more hours than I have yet to put on mine?

I made a (crummy) video of the engine to show the guy that I bought it from that I got it running, and it shows the cooling system, mounting, generator, etc, in case you're curious about the layout or perhaps I've made some fundamentally poor design choices that I need to address. Feedback and your own experience welcomed.
https://www.youtube.com/watch?v=LPBrGu09J9U

Thanks!

--Justin

Been raking in a ton of useful info from this forum, but haven't had a need to post until now. Maybe this question has been answered, but the "search" function is terrible, and I'm not finding the answer. I have a 1999 Metro 6/1 that was only run at the factory. I bought it from a Y2K prepper who never got around to firing it up. Good for me, bad for him. I've read George's CD three times over, cover to virtual cover. I've taken it completely apart, polished many parts, checked many tolerances. I had a local machine shop cut the cylinder liner protrusion from 0.013 to 0.003 and they gave it a quick hit with the ball hone while they had it. The cylinder is great. The rings have light surface scratches which look like machining marks. They are parallel to the direction of the rings. (They are horizontal when the piston is installed in the engine, if that helps clear things up) I have a new-in-the-metal-cap-cardboard-tube set of Lister standard rings. No part number on the container. They look very nice, brand new, never installed. Perfectly polished. Would it make sense to put those in when I put it all back together? I'm worried that the Lister metal might be harder or softer than the Metro rings, which might have been formulated for the hardness of the Metro cylinder liner. I am looking to avoid deviating from the expected metal hardness and cause worse wear on the cylinder or rings. Are the Metro rings exact duplicates of the Lister rings? I've rebuilt lots of engines, but I'm always putting same-brand parts in. Honda rings go in the Honda engine. Ford rings go in the Ford engine. I've never crossed brand lines on critical engine parts, so I'm asking what would you experienced guys do?

Thanks!

--Justin