Home » Public Forums » GMCnet » Little used engine consideration (Broken out of unused engine thread)
| Little used engine consideration [message #336297] |
Wed, 22 August 2018 19:43  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
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Cesar Carrasco wrote on Wed, 22 August 2018 13:10This brings up a good question. I have been starting my gmc's at least once a month for about 10 minutes. I live in southern California, weather is mainly dry and hot. Is this enough?
Cesar,
At least you are thinking, that goes a long ways.
The problem is not the once a month, it is the 10 minutes that they probably idle in place.
Nothing good happens to an engine that is idling. Remember that line and it is hard on flat cam followers. (What most of us have.)
There are two big enemies of conventional little engines. (Remember, I am a ship's engineer.)
Those are:
1 - Thermal Cycles
2 - Corrosion
These two work in close concert to cause damage.
Thermal cycles are every time you start a cold engine. When you do a cold start, parts have to get heated up. Pistons heat up before anything else, and exhaust valves right behind. Then, the head comes along and finally the cylinder block.
The pistons are designed to get hotter than the bores, this is why they are not round and not ever cylindrical. They can take it - more or less.
The exhaust valve problem is the stems, but if the seals are lubricating them right, they will survive. They really only have to deal with the heat for about 20% of the cycle.
But the block and head have a different game. The cylinder block is full of cold coolant and the head is up against the fire ball that you just touched off. On engines with less than effective cylinder head retention, I recorded heads sliding 0.015" along the deck surface with each cold start. This was in a gasket lab, we would cool the engine off, light it and go to WOT. This is what you do not want to do.
Corrosion, on the other hand is a quiet killer. When you burn fuel, you make water - DUH! But because there are other things than just carbon and hydrogen in the fuel, you also make some other things that are acids. These are carried in the combustion by products into the lube oil system. This is the real reason you have to change off lubricating oil so often.
If an engine is run, but the lubricating oil is not heated to a temperature to make the water component evaporate, it and the acids stay behind. While they sit there, they can munch on expensive parts without interruption.
But there is another "Gotcha" coming. Those combustion by-products also get to collect on the internal surfaces like bores and valve faces and rings. Then there is the real big one for us. The entire exhaust system. There is that big long cold pipe to the back bumper. All that corrosive stuff collects there if it is given even half a chance.
I know all about this (Duh - again) but I got a nice warning in Omaha a couple of years back when the sound changed. That last bend at the bumper literally fell off. This was replaced at a local muffler shop and has continued to serve, but it was also a clear warning that the big long pipe under the coach was probably in similar condition. It was. Winter before last, I took it out without needing any tools. The largest piece fit in my trash can.
Now, back to Cesar's case. That ten minutes, unless you fire up and go out to the highway for a nine minute run is doing more harm than it is good. If you have engines that you do not use a lot, better than running them too little is to fog them and then defuel (for carburetor engines).
Fogging is something that every northern boat owner knows well(we put them away when the water gets hard), it is simple. With the engine hot, spray oil into the air intake so all the internal get a coating. That is just that simple. Defueling can be more complex and with our main engines, it is not all that simple. In actual fact, I have never done this to a passcar Rochester. But, if I ever have to, I will pinch off the fuel line before the pump and loosen the steel line at the filter, then run the engine until it starts to falter, then start the fog. When things get quiet, put everything back. The engine can now wait patiently for a year or more and when restarted, it will smoke for a moment, but otherwise be back to its good old self.
Let's carry this one step farther...
On all the RV sites I read that I should run the Onan (or what ever) for an hour a month. They say that this has to be done to keep the windings dry. This is a plan left over from before WWII. We now have better varnishes that are not hydroscopic at all, so that is one excuse that is done, but I do believe that the story is still pushed by the people that sell parts.
Want an Onan to last forever? When it will be ignored for a long time, get it hot (the engine end) and have a can of fogging oil ready. Pull the lead off the fuel pump and give it a minute to jam the governor at WOT. When that happens, start the fog. When it stops, put the lead back on the fuel pump. Now the engine is fogged and the carburetor is about as dry as it can be easily.
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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