WOT Overheat 94 ProV 115hp

[pstephens46]

I've tried to comb back through this thread. Sitting in hotel looking at it with an iPhone. Does anyone see the "recipe " for the citric acid bath op used to clean the head?

[99yam40]

Nope, he said like in instructions above, but never saw any instructions

[KlinkSanford]

I've tried to comb back through this thread. Sitting in hotel looking at it with an iPhone. Does anyone see the "recipe " for the citric acid bath op used to clean the head?

Sorry about that: Here's the instructions:

Here's an instruction sheet I wrote for cars engines and loose parts. On my outboard engines I've only done it as loose parts. For the whole car engine method to be used on outboards, you would have to remove the lower unit and the thermostats and pressure valve and such and use a pump to run the heated water through the passages and keep it re-circulating.

Instructions for Radiator cleaning with Citric Acid


1) Degrease with automatic dishwasher detergent (makes no suds) dissolved in hot water till feels soapy. Fill radiator. Run engine (if easy, remove thermostat, so get good circulation). Run a few minutes to circulate soap around. Engine won’t get hot without thermostat. Drain, and fill once with water to flush soap out.


3) Make a solution of 13 ounces (and no more, others recommended 10oz, but I used the 13oz. and it worked well. The 13 oz measured cup) of the citric acid crystals per gallon of water, it will easily dissolve even before you heat it. With thermostat installed. Run the engine 10 minutes or so after its up to temperature with the citric acid solution inside. Drain. (If a really bad engine, you can do the citric acid twice) when done, flush the system clean water, twice. You will taste the citric acid if there’s still some left to flush.


For car engines you are better off driving around with the stuff inside.


For Cleaning Loose Parts

If you clean loose parts, only when it approaches boiling to do you get the GOOD cleaning action. Do not boil it to the point that the water is rolling over. Just keep the temperature where you have the little bubbles coming up. Boil till part is totally clean and shiny.

If you just throw the parts into a bucket of the Citric acid solution, it will not clean shiny, it will slightly etch the metal, compared with boiling.

[KlinkSanford]

Mercedes Benz flushes it's aluminum radiators and engines with citric acid. I believe they remove thermostat and pour 12% citric acid granules which is first dissolved into sufficient water to fill the radiator. The engine is run for x minutes, and then flushed out with fresh water. I can provide more details later. I've used the method before to flush out an old tractor Perkins diesel that was really rusted bad. With 2 cycle outboards, the question is how do you clean the water passages since it exhausts the water with a mix of unspent fuel? The unspent fuel would create a mess and neutralize the acid. Additionally why would you want to submerge your lower unit exterior in a tank of acid? The solution is that, it must be done with the engine turned off, the gear case removed, and the solution is pumped using a pump through the water tube, and the thermostat must be removed or better yet, I would use an old thermostat that is always open or has the "hat" cut out. That way the water flows like it would when the engine is operating. I bought a 50lb bag of food grade citric acid for $25, which should last me 100 years (I've given some to many friends to use on their cars and equipment and the bag has not been even dented)!

I've seen people mention the use of muriatic acid, vinegar, CLR and other acids, but those are not the acids chosen by Mercedes Benz for their cars. I'll go with MB's Research & Development over that of any tree shade mechanic like me.

Personally, from my experience, the water passages in Florida engines are so bad that the only way to clean them is to take the cylinder head off and scrape all the passages. However, one can't take off the side exhaust cover without great risk of breaking the bolts, so there is a good place to run the acid. I'd say, that if the thermostat is easy to reach, and you are removing the gear case to, say, change the impeller, it might be worth it to go ahead and flush out the engine the way I described. Anyhow, if you want to clean your outboard's cooling system with an acid, use food grade Citric acid, you can eat it, it tastes like sour balls.

The advantage of citric acid is that it is mild, it can be put through the engine to remove corrosion. It also leaves a smooth surface. Like I said above, I would only put it through the engine if I knew the history of the engine and did not want to take it apart. In my case, I did not know the history of the engine, so I took it apart, and good thing, there is no way citric acid would have cleaned this part without scraping. As far as cleaning parts removed from the engine like this head, there are other acids that will work faster, however, they are dangerous to work with. I did this work in my wife's kitchen, she is the master of the kitchen (and a master at cooking so I do not want to upset a good thing) and had no complaints because she knows the citric acid mix is very mild. I put it down the drain when I was done, like putting lemonade down the drain.

[KlinkSanford]

I also used the citric acid to clean the two cylinder head cover plates. They were not as badly corroded as the cylinder head pictured above., but they were close. I had my 13 year old son scrape one of them and it still needed some work. The other cover plate was not pre-scraped. I heated up the citric acid mix as instructed above for loose parts. I put in both cover plates for 25 minutes, and they both ended looking about the same. Definitely not worth all the scraping work my son did. The citric acid batch that I used was old and had been used before, so I think it was weaker than a fresh batch. You can re-use the citric acid, however, this batch had been re-used three times and sat for like 2 years and picked up some mold that I screened out. So, my citric acid was not the best, and the parts still came out clean. At the end I scraped a few soft spots left with a skewer stick and some stainless steel wool, everything was soft. It took very little effort.

The advantage of citric acid is that it does not etch the part, the parts come out smooth. You can also put some in a glass of water and drink it, or make sour ball candy with it. It's not a dangerous chemical.

Here's the pictures, the top cover is the one my son pre-scraped, the bottom one was only cleaned with the citric acid. The bottom one was really bad in the thermostat area and it still came out clean. I think the bottom one actually came out better, though the thermostat area is getting thin. (PS- the gasket material still needed scraping.)

[KlinkSanford]

I don't know how to enlarge the pictures, if you want to read more and see the same pictures enlarged, go to this link:
Flushing Outboards with Citric Acid

[99yam40]

here you go,
all you have to do is click on the pic on the other site to open up the pic, then right click the pic, click on copy image and then come back to the reply on this post and hit paste where you want to put the pic

[KlinkSanford]

here you go,
all you have to do is click on the pic on the other site to open up the pic, then right click the pic, click on copy image and then come back to the reply on this post and hit paste where you want to put the pic

Excellent, thank you. That completes the thread!

[KlinkSanford]

Now that I know how to enlarge the pictures, here again are the pictures of the cylinder head:
1) Before,
2) After 10 minute scraping
3) After the citric acid treatment

[pstephens46]

Thanks for all the detail Klink. I would be more apt to use the citric acid versus hydrochloric acid.

[TownsendsFJR1300]

Thanks for all the detail Klink. I would be more apt to use the citric acid versus hydrochloric acid.

+1 ^^, very informative and very effective procedure, thanks for the tip!

And feel free to stick around!

[99yam40]

where in the world do you buy citric acid in 50 lb bags?

[KlinkSanford]

where in the world do you buy citric acid in 50 lb bags?

It is called Citric acid anhydrous CAS 77-92-9, I bought it at Bell chemical in Longwood, Florida. It was $72 for a 50lb bag (in 2011), because they are wholesalers and had a minimum order charge. It is food grade. Any similar local supplier will have it. Like I said, 50lbs will last the average Joe a lifetime. You don't have to buy 50lbs. Mine is Tate & Lyle brand, Made in Colombia for Tate & Lyle Decatur, Georgia


(PS - It is NOT sour salt no matter what you may read on the internet. That is used in the kosher deli department but its NOT citric acid, its either a sodium or a calcium salt of citric acid so its not even always the same chemical. Neither is it ascorbic acid as some may claim.

For chemical ID you can use the CAS numbers:
You don't want Calcium citrate CAS 813-94-5, or Trisodium citrate CAS 68-04-02; these are sour salt.
You also don't want Ascorbic acid CAS 50-81-7.
These will sort of work but are not as good as REAL citric acid, they are not what Mercedes Benz uses, why invent?

[99yam40]

I use some in small quantities in home wine making.
but I buy in 1/2 or 1lb quantities on line.

have used it to clean up copper metal , faucet aerators, and shower heads before