Little Trucks, Big World

Lately I've noticed that now and then I have to add some oil to my once new engine. It now has about 40K miles. I traveled from Montreal to Carberry Manitoba with about 1000 lbs of payload. Got a new job out here so I had to lug the toolbox, tools, ect, ect. It was approximately 1500 miles, at usually 60-65, sometimes, 70-75 mph. I kept an eye on the oil, was holding good, then suddenly, I was down a liter/quart. I should mention, there's no CAT in my exhaust system, so there's only a new muffler, otherwise straight pipe from the engine. So there's little if any back pressure. Each day during the week, I run about 70 miles roundtrip, to work, and home, Brandon Manitoba, at approx. 75 mph. Im consuming some oil, could it be because my exhaust is without restriction?
It never did that before, what are your thoughts on this?

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Check the oil at a similar interval, like one hour after shutting down. Checking oil at a gas station then shutting overnight then checking the oil will drive you nuts. Once you have consumption established and throw some cardboard under the truck for leaks will give you an idea where to look.

Exhaust would have nothing to do with oil consumption.

If you are running synthetic oil, the next change stop using it. First, you don't need it. Older engines just can't handle how slippery it is and it will leak past old seals and gaskets.

Take the top off the air filter and look at the vent hose from the valve cover where it enters. Is there oil showing?

I would try reducing the highway speeds to 55. '70-'75 is damn fast in a 720. This is less than 15 min each way extra and will reduce the oil fog inside the engine and the blow by that pushes it out.


Speaking of oil...

Look up discussions about how oil makers are reducing the levels of ZDDP a zinc anti scuff additive that is important to 'flat tappet' cams like we still have. All new cars use roller cams and it isn't needed so it's being fazed out. I'm running 15w40 Shell Rotella T4 a light duty diesel oil that still retains the higher level for diesel engines. Castrol, Valvoline and a couple of others still market what they call 'racing oils' that still have the original higher levels.

Mike makes a good point. For the younguns out there these vehicles were sold when 55 stay alive was the motto and highway speed limit. 70 to 75 was for the rebels without a cause. With a modern drive train and brakes they can keep up with traffic but no airbags, abs or doorbeams. Driving a 720 at modern highway speeds is only slightly safer than a motorcycle.

Not really the safety I was concerned with but the extra revs will produce more blow by. If it is excessive  the fine oil fog in the crankcase has less time to settle out and can be pushed out and carried along the valve cover hose into the carb.  

Thanks Mike, you explain it well. I remember having that load and being in traffic. Knowing about the weak countershaft bearing I'd opted to use 4th gear for part of the trip, in some hilly areas. That's where the RPMs were a bit high, say 3000, 3200, it made me worry some, the usage confirmed something was going on. I don't use synthetic in the engine, only Castrol 10-40 standard. I could go for the Rotella 15-40, but here this winter will get low, say -30 to -50 C in told. I'm going to slow it down, I could do 60 mph, I may also get a different vehicle for commuting. Speed limit here is 110K per hour, and lots of folks travel at 120, or better.
I checked the air filter box, in the front, near the small white pad, that filters the oil mist, there was some motor oil present there, a couple of teaspoons worth. The weather is changing up here, I've noticed a slight drop in my mpg, like it's down to 18.5 mpg from 19.7. Back in August I swapped out the valve cover, and air cleaner box from my donor truck. (My original valve cover lost the rear nut that holds the bracket for the air box). Yesterday I re-connected the vacuum line for the ATC, and installed a heater duct, from the exhaust manifold heater plate to the intake snorkel. I'm going to work with that and bring the RPMs down and it should be fine. Thanks again for all the help from everyone.

I drove my 710 last winter for the first time. Nothing like winter driving to show up problems. Carb icing for one. Installed the 'stove pipe' and all good. The hesitation when taking off got gad enough to backfire and blow up the muffler.... cracked coil arcing. Not a problem in the summer just annoying. Now it runs so much better. I'll never drive it in the winter again!

Castrol does make a racing oil with the higher ZDDP level and probably 10W30.





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