Maybe I could get another 100,000 out of my 87 Nissan if I use MMO. It definitely has blow-by .. even at idle.
Eric--- Don't know how relevant this is to your blow-by thing, but back in 1973 when I bought my new Land Rover Series III-88 STP oil treatment was all the rage. At the time the Land Rover was the most expensive civilian 4 x 4 on the market in the US and wanting to maximize my new vehicle's life I fell for the hype and decided to add STP to the oil. As you may recall, STP has a very heavy consistency.
So I poured in the recommended amount in the parking lot of the auto parts store in Honolulu where I'd bought the STP and started driving home. Immediately--- and I mean immediately--- the engine started knocking on acceleration or under load. Away from a stoplight, up a gentle grade, you name it.
Very much alarmed, the next day I went back to the store and bought 8 quarts of Castrol GTX 20-50, the recommended lube oil for the Land Rover in my climate. I went home and changed the oil and it ran perfectly. No knocking.
But being young and gullible I still believed that STP would be good for the engine. Just goes to show you the power of persuasive marketing, right?
So I bought another can and added it to the oil again. And exactly the same thing happened. The engine immediately began knocking on acceleration or under load.
Back to the store, bought another 8 quarts of Castrol and changed the oil again and never put STP or anything else in the oil again.
Although at the time I did not know much about engines, I tried to figure out what had been happening when I added the STP but could not fathom what had been going on. Whatever it was, it had to be related to the STP vastly increasing the viscosity of the 20-50 oil in the engine. This was a brand new engine so blow-by from worn rings would not have been a factor. Knocking is usually a timing issue but I don't see any way simply increasing the viscosity of the oil could affect the ignition timing unless the compression was somehow being affected which then made the ignition timing incorrect under load. So it's still a mystery to me.
But if what was happening was that the STP-thickened oil was somehow affecting the compression ratio, perhaps something similar would happen in your vehicle if you added MMO. I've never even seen MMO so I have no idea of its viscosity.
Or you can try STP if they still make it. Where it made my new vehicle knock it might make your old one run better.
