Tried a 0w30 because thought the thermostat was stuck open. Got a new temp sending unit and all is good. Usually run a XXw-40 in this monster. Next fill is going to be Rotella T6 5w-40 for the winter.
1978 Ford Thunderbird 6.6L 351M 1.2k OCI Mobil 1 Advanced Fuel Economy 0w30
- Thread starter Danimal1q2w3
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That’s what’s currently in the sump
Are you using a Zn in-a-can supplement?
I would be curious what your next analysis would show after running your current fill, servicing your air intake and getting your carb back into shape. Don't overlook a small fuel leak into the crankcase from a fuel pump. Just curious, 6.6 is a 400 cu not 351.
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I wonder why old engines of this era shed so much wear metal? Is the oil too thin? Were the engines back then not as precisionly machined? Was the metallurgy different?
The 351m and 400 were both not known for longevity back then. Nothing like a 302 or 351w. My friend worked at the Ford dealership when they were common and owned a couple he had to replace engines in.
In this case it could be the fuel dilution, dirt getting past intake(high silicon) or corrosion as stated below.
Probably corrosion (rust) inside the engine block from infrequent use.
Yes! Forgot to mention that!
according to the sticker on the valve cover and a few other documents I have, the 351 “m” is a 6.6L and has 400 CID. I am a 28 year old guy, these engines are before my time, so I don’t Claim any expertise, but from what I can tell there’s a lot of confusion around the “m” designation
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The 351M and the 400 (two different engines) are 335 series engines like the Cleveland. IIRC the 400 had the big block bellhousing bolt pattern, which made it less desirable for hot rodding applications in place of a smallblock due to transmission selection limitations.
Main difference between the 351C and the 351M/400 was the deck height. The 400 had a higher deck height to accommodate its increase in displacement relative to the 351C.
The Cleveland family actually has a decent history of excellent performance, with a number of very good flowing heads available for it, in part thanks to the canted valve arrangement. Cleveland heads were used on a Windsor to produce the BOSS 302.
The 351M/400, which were designed for low performance applications did not receive the performance goodies and typically had a broomstick camshaft. So, if you are rockin' the original cam, you definitely don't need a ZDDP supplement.
I had a 351M in a '77 F150. What a gas guzzling POS. "Low performance'? Huge understatement!
I get about 15-16 mpg when I take it easy on her. I wanna get 3.50 rear end to make it not seem so sluggish. I plan to drop a 460 in at some point so I didn’t want to do much to the 351m but I did get an edelbrock 1906 4 barrel carb put in and it runs way nicer, smoother, more responsive, and almost doubled my gas mileage. Not to mention it just sounds better. It’s a fun project car. Only paid $1300 for it
From what I've been told of the 400-351m engine is they prefer a thicker oil like 10w40, 15w40, 20w50. I use to run 10w30 in my 75 LTD but switched it to a 15w40 and its noticeable quiter. The owner manual even says to use a w40 if operating above 55mph over extended periods of time. These engine where known for oiling problems particularly in the cam/lifter area. Thicker oil was the fix I guess .
Agreed. I had a 1979 F-150 with a 351M. Oil pressure was near zero. I added a bottle of Restore at each change and that helped bring it up.
I got rid of the cat and put a 500 Holley 2BBL on; that helped give it some pep. It was a 4WD and I drove it like a mad man. I don't think that I ever got 10 MPG with it.
I got rid of the cat and put a 500 Holley 2BBL on; that helped give it some pep. It was a 4WD and I drove it like a mad man. I don't think that I ever got 10 MPG with it.
I have a edelbrock 1906 4BBL. It definitely made it peppier, upped my mpg from about 8 mpg to 13.2 running ethanol free 90. I use a fuel tracking app every fill up to keep track. Started a new profile after I got a new carb
In the summer I wanna run the castrol 20w50 and see what happens. Gonna move to t6 5w-40 for the cold New York winters. Gonna change it next week actually
EDIT —- it’s been a while since I posted this thread and I realize I repeated a few points from above. My bad
After I posted that I feel like I may have said it before somewhere else as well. It's easy to get lost in all these topics.I have a edelbrock 1906 4BBL. It definitely made it peppier, upped my mpg from about 8 mpg to 13.2 running ethanol free 90. I use a fuel tracking app every fill up to keep track. Started a new profile after I got a new carb
In the summer I wanna run the castrol 20w50 and see what happens. Gonna move to t6 5w-40 for the cold New York winters. Gonna change it next week actually
EDIT —- it’s been a while since I posted this thread and I realize I repeated a few points from above. My bad
You could make it run a stronger with a bit more cam, nothing too overboard, but maybe something like a Comp XE256. Pretty mild with good idle and drivability but a fair amount more lift and duration than stock.
The higher gears will definitely help also.
The higher gears will definitely help also.
Back in the day I owned a 77 Thunderbird with the 351m/400. I bought it from a guy who had it mildly hopped up. That car was fast in a straight line. God for bid a slight turn came up at higher speeds. And I also had a 77 Lincoln Mark V with a 460. Those were the days when gas was$1.00 per gallon so gas mileage wasn't a issue. Have fun with that car.
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