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Ok. So, I've begun the restoration on my 1941 firetruck, and have a question concerning engine oil. After some long discussions with different mechanics (both shade tree and professional) I am left questioning what grade of oil to use in my engine. I have been told to use the following: 30w non-detergent, 10w30, 10w40 and even to find oil formulated for use in diesel engines. So, let me know what you think!
New rebuild - use any 10W30 for the first 500 miles break-in. Change and use whatever you choose. For a marginally used firetruck anything will work.
Current diesel oil is preferred because of the zinc additives that all motor oil used to have for flat tappet engines. Upcoming diesel oil probably won't have this so we'll be forced to use an additive in order to protect the cam and lifters (thanks EPA!)
Old used engine - if you can find it use straight 30 wt non-detergent so you don't loosen old sludge deposits and plug up your oil screen. Leads to oil starvation and ruined bearings throughout the engine.
Scortchin, I agree with mtflat about the non detergent oil. Most of the old motors will have significant amounts of oil sludge built up (my g-grandfather's shop used to run a mix of fuel oil and motor oil at oil changes to keep the sludge levels down -- but most people didn't do that, as I can attest by my teardown of the flatty that I recently bought). I have also heard that the single weight oils hold their viscosity characteristics better than the multi-weights. I have never looked at testing that claim myself, but have heard it from some very reputable oldtime flatheaders. I would say that the weight of the oil should be based on ambient temperature though. During the warmer parts of the year you might want to consider 40 or 50 weight (and of course in Minneapolis today, -16° F, you would want to go lighter). 30 is a good place to start though.
That said, Hotrod did a good article on cams and zinc in a recent issue:
While they say there is still much debate over the cause of higher rates of cam failure, they do say that the zinc additives (or specially blended racing oils) might be a good proposition for the old flat tappet engines like our flatheads (especially if you are running high pressure springs). They do go into good detail about why the zinc has been slowly removed from the motor oils.
1. The zinc phosphates are consided to be toxic heavy metals like lead.
2. Most engines no longer require it.
3. The zinc messes up other fuel economy/emissions systems on newer cars.
So I guess IMHO, since most cars no longer require the zinc, if I determine that I do need it in my flatty, I will do my part by only "burning" it only in the flatty and not in my commuters.
I just happened to have my '48 operator's manual in here today - engine oil recommended is:
Temps above 32F - SAE 30
Minimum temp above +10F - SAE 20
Minimum temp above -10F - SAE 10
Minimum temp below -10F - SAE 10 plus 10% Kerosene
Remember that according to Hotrod the changes in oil components was dictated by the car manufacturers. Here is what Shell says about Rotella:
"ROTELLA T Multigrade is a universal oil, meeting API Service Categories CI-4 & CI-4 PLUS for diesel engines, and SL for gasoline engines. Where the engine manufacturer recommends oil meeting either one (or both) of these Service Categories, or earlier categories (like API SF), ROTELLA T can be a good choice.
However, ROTELLA T does not meet all the requirements of ILSAC and API Certification Mark (starburst symbol) standards, sometimes specified for gasoline engine oils (in addition to API SL). These additional standards deal with fuel economy, and also limit phosphorus content (an element in all engine oils, but usually at a higher concentration in diesel oils). Phosphorus can affect catalyst activity in some exhaust emission control systems.
If your manual specifies only API SL (or earlier designation), then the catalyst is likely not sensitive to higher levels of phosphorus. If it also specifies ILSAC standards, using ROTELLA T may risk some catalyst activity loss.
Against the risks noted here, the advantage of using ROTELLA T comes from its more robust performance controlling engine deposits and wear. "
I don't know if I would recommend a high detergent oil in a sludge filled old flatty. Although I suppose if the detergents slowly cleaned up the motor it would be great -- I would just fear that it would loosen the sludge in the crank and plug it. Are you running the Rotella in a rebuilt flatty or an old runner? I think it would be interesting to find out how many people run detergent oils in old running flat engines without trouble.
Since I will rebuild mine I will run a multi weight detergent oil, and just because of the cost of parts on this thing, I probably will run a synthetic like Rotella, but I have had good luck with regular oils also. I have about 300,000 on my '76 F100 302 (rebuilt once with new pistons, and bearings, but still has the original cam and lifters).
I started working for the USPS back in 1957. The mail delivery fleet was flat head Dodge, 6 cyl Ford among others. They were being run with low temp thermostats, and who knows what for oil before I started. They went to 180 stats MIl 2104A oil (the first HD oil) and dislodged some quite somesludge in those engines, I'm sure. When you would pull one down for a valve job you still had to spend quite some time to see the springs, however we didn't have any screen plugging.
If that were my Ford truck I would add a quart of ATF to the present oil run it
for an hour and drain it. Refill it with some 10/30 and change the filter if it has one and run it for a few hundred miles then repeat the exercise and run it a thousand. I would also equip it with a bypass filter if you can find one if it isn;t there. A couple of hurried oil changes will clean up i a lot of the mess which I'lltell you I don't think you'll find to bad on a flathead V8. You can see the inside of the engine real easy as the intake comes off in 20 minutes and the major area where sludge will accumulate is in front of you. There isn't much room around the timing gears.
I pulled my intake and oil pan cleanout first. everything was clean so I went on ahead and ran detergent oil. it still turned black fairly quickly but cleared up after 3 or 4 oil changes using engine flush. I assume that was just from crap in the crank throws. it stays pretty clean now. there are plugs in the cranks of these engines and if they are not pulled during a rebuild and cleaned out that sludge stays in the crank. I'm sure my engine wsa rebuilt during its life and most likly the crank just had some stuff left in it.
My flathead 6 likes to leak the 10-40 and tends to go through it faster, I have used 20-40 or 20-50 whatever is on sale, and it works well. I have never had good luck with 10W in a Flathead, but then again, I have never owned a new, or rebuilt, Flathead. I have always been able to get them running and drive them as is. That's part of the experience I enjoy these days, driving them instead of going out into the garage and looking at them sitting on an engine stand like I used to do 35 years ago.
__________________ Rod 51 F1 Truck Flathead 6 / 3.23 Rear S-10 5-Speed "Keep on Truckin"
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