oil

[Alan O'Connell]

Is 5 w 30 to thin for a 36 flathead?

[paul2748]

Lots of different opinions on oil. What to stay away from is oil marked "For gasoline engines only" as this is oil for the modern roller engines. Personally, I wouldn't use anything lighter than a 10-40.

[Bored&Stroked]

In my opinion, the answer is 'Yes' - I think even a straight 30W would be better than a 5W. BUT - I have not attempted to try it, so this is just a gut feel.

[JSeery]

I like lighter oils, but I think 5w 30 is too thin myself, I would want something heaver weight. Same as Bored&Stroked nothing to back that up.

[40cpe]

Ol' Ron will check in. I THINK I remember him saying that he liked 5w-30. Of course, he's in Vermont.

[Jack E/NJ]

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>>>Is 5 w 30 to thin for a 36 flathead?>>>

I've only used Motorcraft 5w-20 synblend since rebuilding my 21-studder 6 years ago. So 5-30 might be a bit too thick when it's hot. 8^)

Jack E/NJ

[JSeery]

I think these oils are designed more for the roller lifters/followers and the heavier oils for a flat tappet cam. But Jack says it works for him, so I guess only time would tell if there is a ware difference. It may have more to do with the additives than the weights, I'm certainly no oil expert!

[RalphM]

I use straight 30 wt. for the limited season we have.

[Drbrown]

My 1980's snow-blower manual says 5w-30 below 32 degrees. But since we're not driving snow-blowers on highways and interstates, and that I live only a two-hour drive south of Canada, I choose to use 10w-30 in my 59AB that has 35,000 on its rebuild. Gauge reads 70 lbs cold and 15-20 lbs hot. I currently have no filter on it, change the oil every 1000 miles, drive it at least an hour each run, and don't need to add oil between changes. So I'm good for now.

[Lawson Cox]

I use straight 30 weight down here in the sunny, but cold at the present time, South.
Does me proud.

[TomT/Williamsburg]

If your flathead has not been rebuilt, chances are it's an original engine or was rebuilt some time ago. That would mean using a straight weight non-detergent oil ad Henry did. If the engine is older running a detergent oil could cause you some problems. Others hopefully will chime in here on this subject as well ....
If it is rebuilt I would use 20w-50 as I have in all of my rebuilt engines with a bit of zddp added and I run no filter but change my oil frequently ....

[Alaska Jim]

I use either Chevron Delo 400 or Shell rottella 15-40. been using it for 15 years in my stock 8cm '51 Merc.

[Hoop]

"Is 5 w 30 to thin for a 36 flathead?"

No, it's not too thin. Why would you think it's thin?

Oh ... the 5W.

After all that's been written about oil, it is amazing how few understand the numbers.

First the "30". That is a viscosity GRADE, not a weight. So 5W30 has a grade of ... 30. So-called "straight weight" 30 also has a grade of ... 30 ... and is labeled SAE30. Both have a viscosity flow approximately the same at OPERATING temperature.

0W30, 5W30, 10W30 and 20W30 all have a viscosity grade of 30 at operating temperature.

What's 5W? The W means WINTER. It does not mean "thin". It does mean that when it's cold, your oil will not flow like molasses but will try to flow closer to 30 grade, bur not thinner. It's not going to be some weak, watery stuff.

At cold (cool) start up, even in the South, SAE 30 ("straight weight") is thicker than it is at operating temperature. Most wear occurs at start up ... why would you use that crap when a multi-grade oil (note it's not called "multi-weight") will lubricate your engine better?

5W, 10W, etc. all indicate the oil's ability to flow closer to the viscosity grade when the temperature is below operating level.

If you want a 30 grade oil, pick the Winter rating you want. Keep in mind that the stuff they put into the oil to do this viscosity magic can break down with extended or extreme use like racing ... but for our engines, old or new, multi-grade is the only wise thing to use.

Note:

"In my opinion, the answer is 'Yes' - I think even a straight 30W would be better than a 5W. BUT - I have not attempted to try it, so this is just a gut feel."

(Same thing happens to me. Stay away from broccoli.)



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[Kurt in NJ]

Have you looked in the owners instruction book---it depends on the temperature

I only have a 1937 listing--
above 90 degrees--- 50wt
100-30 degrees --- 40wt
65--20 degrees--- 30wt
50--0 degrees--- 20 or 20W
30-- minus 15---- 10 or 10W
-10 or lower --- 10wt + 10% kerosene


From this listing it would appear that 5W 30 would be good from 65 degrees down to well below freezing

[JSeery]

Thanks Hoop, very informative! I looked up the temperatures used to establish the ratings, that is interesting as well (at least to me). The straight SAE viscosity is measured at 100 deg C (212 deg F). The W SAE viscosity is at various low temperatures. It would be interesting to see a viscosity curve between the low and high test points to see what the viscosities are at the temperature ranges that a flathead runs at.

[Kube]

Originally Posted by TomT/Williamsburg

If your flathead has not been rebuilt, chances are it's an original engine or was rebuilt some time ago. That would mean using a straight weight non-detergent oil ad Henry did. If the engine is older running a detergent oil could cause you some problems. Others hopefully will chime in here on this subject as well ....
If it is rebuilt I would use 20w-50 as I have in all of my rebuilt engines with a bit of zddp added and I run no filter but change my oil frequently ....

In my humble opinion, your advice is the best thus far.
These old flat head engines do not have the tight tolerances of today's engines and as such require thicker weight oil for proper lubrication effect.
Thinner weight oil is utilized primarily in tighter tolerance engines.
Anything less than straight 30w on a used flat head is too light in my opinion. On a rebuilt, most likely to tighter tolerance than Ford produced, yeah, a high quality 20w/50 is to me, perfect.
Our new Mercedes requires 0w/50. yep, you read that correctly - ZERO w/ 50. I can only imagine the tight tolerance built in this engine. And hey, I was a tool maker... I know tight tolerances!

[30-9]

Straight 30 in winter months?

[Joe Immler]

I agree with TomT and Kube. I have had 2 flat heads rebuilt by a professional re builder. He recommended 20-50 as well as ZDDP. I live in Ohio and basically only drive in summer.

[Hoop]

'That would mean using a straight weight non-detergent oil ad Henry did. If the engine is older running a detergent oil could cause you some problems."

Kube, you think that's the best advice? So-called "straight weight" is killing your engine on cold starts.

I explained that "weight" is an incorrect term ... it's GRADE when you are talking about viscosity. Oil is not labeled by "weight."

Not sure what your point is on the 0W50, but if you are saying that the "ZERO" means it is a really thin oil, you need to reread my earlier post. What Mercedes is saying is that it requires 50 Grade oil at operating temperature ... and wants to prevent that 50 GRADE from getting any THICKER when the engine is started cold with cold oil.

No matter what one's opinion is, using the correct terms and understanding what multi-grade oil really is helps the discussion.

Many folks completely misunderstand multi-grade oil. If an engine runs best on a certain GRADE oil at operating temps, then it will run best cold on the same GRADE. The problem that oil companies have solved is that straight GRADE oils are thicker when cold and the GRADE changes. Modern oils attempt to maintain the same viscosity through a temperature range from cold starts to operating temps.


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[edhd58]

Here is my response. Fresh major rebuild of a 226 G 6 cylinder flattie, less than 10 hours. running 10w30, sitting idling in my drive while I wash the car. At some point I get in to move it and see NO oil pressure. I have no idea how long it ran that way. Motor now has just a slight rattle it didn't have before. Changed oil and went to 20w50 just to see if that would help as I was told 10w40 was too thin for the type oil pump I had. Nothing helped. I finally took the engine back apart, had the oil pump machined to get the clearances tighter and now run straight 30w. NO problems since. was it the oil pump or the oil I do not know. I was told by a guy that knows that style oil pump NEVER run less than 30w in the G series 6 cylinder because of that style oil pump. I was told by the same guy that once the film in the pump disappeared because of thin oil it would not pick up oil again until I primed the pump, because it hangs above the oil not submerged in it.