Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I filled and bled the system of air on mine ( cranked it by hand after filling the radiator, and topped it off with a blunt needle syringe through the top water jacket connection with the fitting removed)  and leave it wet. Unless you’re concerned about freezing, not an issue I don’t think.

I have never put water in mine, never needed to.

Quote from: St Paul Steam on January 08, 2021, 06:19:18 am

I have never put water in mine, never needed to.

Does that have any effect on the water pump being run dry Bruce?

Nah,  I put a drop of oil on the pump piston & forget about it. I don't run it very often.

Hi All,

Do you fill your M91 radiator with water before running and if you do, do you leave it full or drain after running?

Hi Jim, I filled mine just once to test it and check for leaks. If you are running it slowly enough it will not ever get to hot.

One very easy to fix issue is many of these were assembled with the upper water pump check valve in upside down which put undue pressure on the pump and caused water to be pushed out past the piston. 

Bottom line is this engine should not get hot enough to ever need water unless it is pulling a substantial load. If you have a laser thermometer, you can check the head temperature after it has been running for a while. Also, 

If you decide you want to keep coolant in it, I would suggest a 50/50 mix of automotive antifreeze and distilled water. If you do this I would suggest that after a few weeks you check the crank case by tipping it over until the vent hole (plug out) is pointing straight down. This is just a precaution to see if any coolant is getting past the lower water jacket seal. This is unlikely but I have heard of it.

Gil

A small load like this...
works fine without water:

Jim, just like a car engine, if the radiator and pipes to and from get warm, that’s a pretty good clue.

That engine really doesn't need coolant unless it is working hard.

You can run it for an hour and it will not get too warm even with no coolant.

If you have antifreeze in it you can leave it if you want to. Distilled or tap water will cause corrosion over time. The aluminum will likely deteriorate first.