MMO and/or ATF in fuel

[Sharps40]

Question time...looking for direct experience.

Problem: Modern high alcohol/low boiling point fuel and carb boil over about 20 minutes after shut down.

Yep, phenolic spacer and heatshield is the best solution for this modern fuel that works well under 35 PSI in EFI but not so much in carbs...but

Marvel Mystery Oil and/or ATF at 8 oz oil per 10 gallons of gasoline is touted as a cure for shut down boil over.

Internet myth or are ya doin it successfully?

If successful, MMO or ATF as your choice of Boiling Point Modifyer?

[64fleetside]

I seek out the few stations who still sell it ethanol-free, and a few more are popping up. I keep a few 5 gal cans around also. That stuff simply ruins small engines, voids any warranty also.

[Sharps40]

Ethanol free is getting hard hard hard to find.....

[463]

just click on you state on the bottom of the page
http://www.pure-gas.org/

[61K10]

Good old kali only 5 stations, and in way northern kali

[cortcomp]

I know a lot of guys in the packard community run 10% diesel mixed with gas to help with vapor lock issues and it for sure has worked for many. once i put the phen spacer and correct factory heat shields in place, i had no vapor lock issues so never tried the diesel. That being said, i see no reason why then that adding MMO or atf wouldn't change the boiling point slightly. I'd wonder how well it stayed mixed, only time would tell.

[cortcomp]

Also, how hot are you running normally? I haven't had any modern fuel issues even when i had some timing and other issues that had my 455 running at 210 degrees for a whole weekend, and it was 114 out (last summer, it was brutal). Carb was great. Was rebuilt with parts for modern fuel/alcohol though, so it wasn't eating up seals, etc.

[markeb01]

I had fits with this problem for a long time. The cure for me was the 1/2" isolator/spacer, blocked intake manifold heat, and elimination of the heat riser. On a 100 degree day the engine can hot soak up to 210 and it still fires up immediately. Boiling is completely eliminated. It never occured to me to try blending something in the gas. Years ago I used to run the drip style Marvel Inverse Oilers, and can attest they keep the top of the engine looking like new.

The only remaining problem I encountered was evaporation of the gas in the fuel bowl if it sat for a week or two. I added an electric fuel pump by the tank to fill the lines and carb after sitting for long periods. It is wired on a momentary switch specifically for priming. Once that is achieved the engine starts up easily and runs on the engine driven mechanical fuel pump.

[Sharps40]

I'm runnin a 6 with Weber 32/36. I've blocked the manifold heat off completely and still get some perk on 60 degree days. Its only on shut down, about 20 minute soak. Restart is always easy though. Marvel, 4oz per 10 gal didn't work yesterday or today. So, next is to pull the carb and check the needle and seat for dirt...but not satisfied that's it since it never loads up on idle no matter how hot...but come back after 20 minutes and watch and hear it burble like an old coffee pot.

I am pretty sure I'll have to make up spacers from phenolic or oak and add a heat shield between the bowl and the logs.

The oil was worth a try though...sure smells nice when ya spill it on yer hands and shoes, minty at first then like good ol 3 in 1 oil!

[ChuckW]

I've used MMO for years and have never had any issues. Can't say if it will cure your issue. BUT, it's can't hurt either. Try it in a couple of tanks and see what you think. It "should" help as it will dilute the alcohol some while adding a bit of oil the help lubercate your upper end!
But you should probably have a heat sink between the carb if you are boiling out the gas after a 20 min soak..... IMHO... Cheers

[luvbowties]

Originally Posted by Sharps40

Question time...looking for direct experience.

Problem: Modern high alcohol/low boiling point fuel and carb boil over about 20 minutes after shut down.

Yep, phenolic spacer and heatshield is the best solution for this modern fuel that works well under 35 PSI in EFI but not so much in carbs...but

Marvel Mystery Oil and/or ATF at 8 oz oil per 10 gallons of gasoline is touted as a cure for shut down boil over.

Internet myth or are ya doin it successfully?

If successful, MMO or ATF as your choice of Boiling Point Modifyer?

Hi Sharps, I had a thread on here a short while ago re: boiling over on a stock 327 with 300 hp--while driving, on hot days--using the AFB 4bbl(perhaps identical to today's Edelbrock) from back in the '60's. Happened intermittently, and we tried all the known logicals first--finally cured it by placing a heat dissipator between carb and original 327/300 hp cast iron manifold.

One of our 1st attempts was to lower the floats as low as possible(to allow more unused bowl to contain the fuel-expansion) and still avoid stumble on acceleration: no avail. Another tho't was to raise floats as high as possible to supply greater volume of fuel which hopefully would be too much for the heat to boil so easily: to no avail. Tried adjusting timing as well as cooler thermostats to lower engine temperatures: still no avail.
When it happened, I'd raise hood, raise the removable rods(each held by 1 screw and a tab), replace them with NO other change, and go back running correctly. Finally determined the time taken doing this had more to do with cooling--than rods raising-and-falling improperly--so after this cooling-off period, it went back operating as sweet as could be asked.

So, it boiled down(not intended as a pun!)to dissipating the heat with a proper spacer. Hope your cure is as simple as this was--even tho' ours came after wasted expense of hours of experimenting and a few inexpensive parts. We finally used a dissipator, which we had to modify slightly with a dremel grinder, that my partner had lying on a shelf, w/out our knowing its composition(phenolic?) or source...but it worked!

Assuming you must be using some type of adapter(s) to mount your carb, you may even benefit from using, like 2 dissipators: one between manifold-and-adapter, and 2nd one between adapter-and-carb. Shouldn't cost but a few dollars to buy/build one or two heat dissipators to try. Hope it works as well for you.
Sam

[Rich 5150 69]

Several people I know had the same issue, changed to a edlebrock air gap manifold, prob solved...

[Sharps40]

Yep, I'm thinkin the spacer is the ticket. But I've learned to do what Tom Langdon at Stovebolt Engine Co says with reguard to the carb and hei too....so, he recommended checking the needle and seat first for trash. Todays job. If that don't clear it, I'll order a pair of phenolic spacers and prolly wipe up some sort of blanket or shield to go between the log and the bowl.

The only problem has been the smell...starts are fine but leaks ain't right and its gonna be harder on my cylinders/valves in the long run washin em clean and dry with each hot restart.