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Air cooled engine question


dwwilson44's Avatar
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09-19-08, 09:33 PM   #1  
Air cooled engine question

I have a 30 hp overhead valve air cooled engine that runs my standby generator. I have been running Mobil 1 synthetic 10w-30 in it and it is using about 3/4 of a quart per day. I checked further with the manual and they now seem to recommend this weight at lower temps and sae 30 in the summer. No one makes a 30 weight synthetic that I can get locally. The breakin oil was also synthetic. I would like to use the sae 30 wt to try to reduce oil consumption, and have read that it is now ok to move between synthetic and regular oil. I have read in other posts that 30 wt is better in air cooled engines than multi viscosity oils. Can I now safely add regular 30 wt oil? Thanks.

 
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j HOWARD's Avatar
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09-19-08, 10:25 PM   #2  
I don't see any snow on the ground.
If you are really worried about it--drain it & add 30 wt. oil.
I run 30wt. in my generator year round--no problems yet............

 
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09-20-08, 06:19 AM   #3  
3/4 quart per day is not bad oil consumption if you are actually burning that much for 24 hours of run time. That is 4 ounces (.03125 quart) per hour. It's a bit high but still within the normal range.

I know this is too late for your generator but when breaking-in an air cooled aircraft engine you use a traditional dinosaur based oil and run the engine hard (65% to 75% power) to keep cylinder pressures high enough to seat the rings properly. Going easy on the engine or running synthetic oil during break-in prevents the rings from seating and you end up with excessive blow-by and high oil consumption. Synthetic oil works too well. It prevents the friction & wear that is critical to the break-in process.

If your generator still has low hours and you want to waste a lot of money on fuel I would put in a traditional mineral motor oil (I actually pereffer multi weight) and try and break it in again. With the traditional oil run the generator for 10-20 hours under a 75% load. I assume your generator is about 13kw to 15kw, so come up with 10kw to 11kw of load (electric space heaters work well). More load will create cylinder pressures & temperatures too high and may glaze the piston/cylinder. As a comprimise just put in mineral oil for about 50 hours of run time and then switch back to your multi-weight synthetic oil and see if your oil consumption improves.
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To make you feel a bit better, it is considered normal for a 4 cylinder (160-200hp) aircraft engine to burn a quart of oil per hour. That would be 6 gallons a day!

 
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09-20-08, 04:19 PM   #4  
Thanks

The unit was broken in with oil put in at the factory . I changed it out and misread the manual after the break in and put in the synthetic. But from what you are saying, I would probably have the same oil consumption with 30 w and I have now. I will continue to add the synthetic until we get power back in our area in Houston and then before the next hurricane I will put in 30 w. You are right about the oil consumption, I was just concerned since the capacity is a little less than 2 qts

 
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09-20-08, 04:38 PM   #5  
I would stick with the synthetic especially if you are puting a lot of hours on it. I doubt your oil consumption will drop with straight 30wt oil. If you do try it report back, I'm curious to see if it makes a difference.

 
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09-20-08, 05:19 PM   #6  
Thanks

I will report back, but I hope you have to wait a long long time for the report. I am not going to move off the synthetic until we get our power back in Houston. I hope to have many many years before I have another extended run. It has now been runing full time for over a week with only down time each day to add oil. I have heard that someone makes a unit that provides the additional power needed for compressor start up to smooth out the surge in load the generator has to meet when the a/c kicks on. It causes a very short term transient in a couple of my cirucits in the house. It has plenty of capacity for what I have connected, I just would like to eliminate the transients.

 
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09-21-08, 05:18 AM   #7  
I would hate to see your fuel bill! Are you able to buy fuel or did you have a bunch stored?

Even 150 miles inland I've been without power three times for more than a week. Often the gas stations are without power and cannop pump fuel so I have to keep large amounts on hand (first their is hurricane season then it's followed by ice storm season). I have a small Honda EU2000 generator to run for long periods to power some lights on and the TV. It is very quiet, efficient and cheap to run all day long (it runs about 6 hours per gallon). Several hours a day when we need AC or to run the well pump I run the big generator which is a 13kw that runs off the PTO on one of my tractors. The big diesel engine and intertia of the drive system handles those shot transient loads very well but it is loud and drinks a lot of fuel (3-5 gallons per hour).

 
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09-21-08, 08:35 AM   #8  
Fuel Bill

The fuel bill will be about 1.5 - 2 times what my power bill would have been. It is tied to a natural gas line so I am not having to buy any gasoline at all. With a simple conversion of settings on the unit it can also run propane. I went this way because I did not want to store gasoline and have to run all over town to try to find gasoline. I went this way because of this situation - when a hurricane hits our area has lost power for as long as 2 weeks. I need power since I work out of the house and with the generator I can continue with my consulting practice. The generator is just another cost of business that has the side benefit of adding a lot of comfort.

 
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