The Stovebolt Site Forums The Shop Area Engine Shop 235 engine block coolant drain.

On the rear left side of my engine block, 3 or 4 inches above the oil pan seam, there is a tapped hole, apparently for coolant drain from the block. Last winter (I know - for some it still is winter) I drained the block and radiator, just for good measure. So now, I am re-filling the coolant (anti-freeze this time for permanent solution), adding it through the thermostat port. I notice that no fluid is flowing out the block drain port (it did when I prepped for winter). However, if I blow air back into the drain port, it bubbles right back out the thermostat port. Am I just not getting the coolant past the water pump?

Hi Bob...sorry but you've confused me. The tapped hole is in fact a coolant drain for the block. Are you filling the engine via the radiator? Or do you have the upper hose removed and are you pouring coolant in that way? If you're adding coolant through the radiator, I'd expect it to begin coming out of the engine coolant drain hole as the level increases (from bottom up)...remember the thermostat will be closed if the engine is closed and the thermostat is working as it should.
Jon

I have the upper hose AND thermostat removed and pouring in coolant that way (the hole where the thermostat was).
Bob

Try poking a thin wire in the hole. Coolant should be coming out if it isn't corroded or plugged up...
Jon

Thanks. You've confirmed my fears. Is there any sort of effective block flushing?
Bob

There used to be, but today I'm not sure. I haven't had any engine nor radiator flushed in many years. In the 60s, places that did this were common. Flathead Ford owners kept many of them in business.
I'd call around and ask shops in your town what they'd suggest...who they might use for something like this, that is. I've heard guys older than me say they used agricultural molasses mixed with water to dissolve rust, but I don't have any experience with that and couldn't tell you how to do it. It isn't like the molasses you get at the grocery store. You'll need to get that stuff at a livestock feed store or ag supply store.
Jon

Be careful of having a shop power flush the coolant system, as these old radiators and heater cores can't handle much pressure. I would do as already recommended and dig around with a wire until you get some flow, then put in the proper petcock.

After removing the coolant petcock from the driver's side bottom back of the block, I found the coolant channel was clogged in both directions on my 51 Chevy 3100 with a 61 235 in it.
After digging out all of the coagulated sediment that I could with wire, I took an old motorcycle clutch cable and cut the outer jacket 6-8 inches shorter than the inside cable and hooked the drill to one end.
Used the jacket to guide the cable in and around the corners at the back off the petcock hole , then used the variable speed drill to turn and push the inner cable in and out and routed out all of the gunk that was in there. Put a hose in the radiator and once it broke through kept running the cable back and forth, in and out, until the water came out clean.

Good idea! I've done the same thing with a retired speedometer cable. That only clears a tiny channel through the crud at the bottom of the water jacket, however. Once the drain pathway is cleared enough to flow, use a heavy dose of muriatic acid (technical grade hydrochloric) in the cooling system and run the engine until it gets up to operating temp, flush with clear water, then neutralize the acid with water and a couple of boxes of baking soda. It works much better than any of the commercial radiator flush products, and any big box hardware store will have the acid by the gallon. It's used for cleaning up after masonry jobs.
Jerry

Z71tank,

Your solution to the problem sounds good.

Just a note that you rekindled a very old discussion that has been silent since 2014 - haha.

Welcome to this site and look forward to further discussions.

Dan

Thanks for the info Hotrod, I may do that when the weather warms.

Hey Gdads51 Dan,
I came across this site a year or so ago when I to find info on the web about clearing out the port in the 235 block. I got so immersed in all the info and good people that I ended up joining.
Also as an addendum to my original post, after boring a hole through the sediment I would take a pair of pliers and bend and fray the end of the cable a little bit more each time and then send it back in like a Roto-Rooter

Thanks for the welcome,
John

HRL has it covered, but here is a Permatex product that I've had good luck with, it has 20% hydrochloric acid in it:


https://www.permatex.com/products/s...ex-heavy-duty-radiator-cleaner-32-fl-oz/

Thanks! I'll remember that. For greasy deposits in a cooling system such as engine oil or transmission fluid from a damaged cooler, a heavy dose of Trisodium Phosphate (concrete cleaner) will cut the oily mess in a hurry. Repeated flushing with plain water will remove it- - - -no need for a neutralizer.
Jerry

Muratic acid will eat rust off of ferrous metals real good; however, it will also eat aluminum. I use it all the time to restore cast iron cookware. Poured some in an aluminum baking dish once... ate right through. So, beware an aluminum radiator.

.

Putting antifreeze in it is a very good idea, even if you don't need it. Antifreeze does a lot more than just keeping your engine from freezing. If you don't want to mess with all those chemicals, powdered Cascade dishwasher soap does a fine job of cleaning also. Put about a half a cup in the radiator and run it for a few days and flush it.

After you're done poking and prodding and flushing, consider installing a coolant filter.

After seeing how much sediment falls to the bottom of the water jacket I knew I'd not be able to get it all out of the block and head. And you'll get more sediment from carbon etc. later. So I installed a coolant filter, NAPA #4070 for cooling systems of about 4 gallons. They also have sacrificial zinc etc. in them. I took a remote filter base off an old 220 Cummins and put a new spin-on element on it. You can buy a remote filter base from Summit or whomever that takes that filter thread and use the number I gave. Or you can do your own research and use something else. I just cut one open after 4,000 miles which was completely plugged with black sediment. Obviously I didn't get it clean enough on the last overhaul.

From my experience with Cummins diesels I've developed a theory that the sediment comes from head gasket leakage over time. Even with all those bolts, the head bounces up and down a little under full load and it'll seep exhaust gasses into the coolant. I used to see trucks from the Chicago run that ran east and west over the Cascades and Rockies come in to the Seattle shop for maintenance. You could tell who'd been pushing them to the max from the streaks of dried antifreeze running down the block below the head gasket. On these I'd look for head bolts with the heads popped off. I found more than one. They'd get a note in their dispatch box.

Most often, it is not sediment which blocks the bottom of the water jacket. It is most often caused buy a stop leak product used over the life of the engine so that a leaky, and very expensive radiator doesn't need to be replaced. The tell is that it is hard as a rock and needs a lot of mechanical effort to remove all of it.
These trucks were work horses, many of them owned by poor farmers. Road hard and put away wet. They did what they needed to do to get whatever job they needed to get done before dark. They likely didn't have time to replace a radiator, nor have the walking around money to spend on a radiator.

What 52Carl said. My 54 sat for 2 years with the radiator out with stopleak in it and I had to throw it away and get a new one.

If you run pure evaporust instead of coolant for a few months
It slowly dissolves the old stop leak and the evaporust will turn as black as used oil. Repeat as needed.
After I did this procedure to one of my 53 trucks the engine no longer overheated and the coolant stays looking bright green.

However evaporust to fill the coolant system isn’t cheap
and two treatments might be on par for a replacement used radiator.
-s

Do you know what the active ingredients are in evaporust? Some kind of acid?

It’s a chelation liquid
Not acid not basic
It modified water’s ability to dissolve otherwise non water soluble salts and oxides
For instance aluminum oxide and iron oxide become soluble like table salt but slower in water with a chelation molecule

Chelation is also used in medicine to pull metals from your body
It’s not a straight forward chemical it’s a family of large organics that do this trick and they are manufactured in large volumes for industrial processes
But evaporust is suppose to be environmentally friendly and safe for your skin and disposal is only critical to the metal oxide you used it on, so if you clean up a lot of lead for instance then that would be bad to dump
But iron and aluminum would be safe to dump as iron and aluminum make up a large faction of normal soil.
-s

https://chem.libretexts.org/Bookshelves/General_Chemistry/Book%3A_Structure_and_Reactivity_in_Organic_Biological_and_Inorganic_Chemistry_(Schaller)/III%3A_Reactivity_in_Organic_Biological_and_Inorganic_Chemistry_1/02%3A_Ligand_Binding_in_Coordination_Complexes_and_Organometallic_Compounds/2.04%3A_Chelation

There are knock off brands of evaporust that work 90% as good
And cost less
Most automotive parts stores carry one or both

Wall mart is the cheapest on average for brand name evaporust I have found

-s

I used to buy a gallon of Evaporust from Amazon for about $16 with free shipping, but it's nearly double that now. Haven't priced it at my FLAPS or Walmart, as my need for it is much less and I still have some left for small parts. It would take a few gallons to fill the cooling system.

Wow, I have a little background in chemistry, but that link went WAY over my head. All I know is that Evaporust works.

Yeah it’s becoming pretty ridiculous priced
I collected a bunch of the 1 gallon jugs slowly at about $16-17 price and that’s how I was able to do a coolant flush and I was expecting the liquid to be still partially usable after
It took about 5 jugs because no heater core
And when I drained it into a bucket to save I saw it was completely used and black so there is was more to dissolve in my water jacket.
I did a second round but it’s getting pricey and I’ll think long and hard before I do it again

But the results were great!
-s

As costly as Evaporust is, it's cheaper than an engine rebuild.

I think I'd try some more usual coolant flush product before deciding it needed the Evaporust treatment. Like 2ManyTrucks said, if there's a lot of rust in the system it burns thru the Evaporust in short order. Even if you do use it, it would be better to flush the block with cheaper stuff first to get all the loose rust out first.

Oh yeah always flush out as much as you can
I made a pressure washer adapter that screws to the back drain hole on a block so I can open up the radiator and blast out rust before deciding on other cleaners
-s

2014 yes, I think it’s possible when doing a search to come across a thread and be tempted to comment on the thread and then looking and realizing it’s from a decade or more ago. But this can happen.
Turns out it’s a good discussion though 😏

Can you mix evapo-rust with water or must you use it full strength?

It wouldn't work as well when diluted, so to really get it to dissolve the rust, you have to go full strength.

I have a 55 235 that is still in the pickup, but I have the whole front end off so it is easy to work on. I have a brand new radiator, not yet installed, so I want to get this junk out before I put it in.

I soaked the whole engine in vinegar for about a week. Then pulled the thermostat out and connected the water pump directly to the water discharge. Ran the engine until it got hot. Left it sit for another week. Then flushed it out. Got out enuf rust to make my own movie.

Removed the drain plug at the back and no joy whatsoever. Black tar like gunk. Poked and prodded, no joy. Hooked up water hose direct. No joy. Pressure washer as best I could. No joy. Left it open.

When I try to push something in there, there seems to be something hard fairly close to the opening. The gunk is somewhat hard, and it is hard to tell if it is gunk or metal. I think it is metal. So I don't want to get too aggressive. I don't know what the architecture is inside of that hole, which direction the channel is (gotta be up) and how aggressive I can be. Don't wanna bugger the threads. Think I'll leave a small 1/4 nipple in there to protect them while I'm fishing.

Pulled the water pump and used a long stick of #6 copper wire, water hose, pressure washer, elbow grease, and a liberal sprinkling of choice words. My roughneck and I repeated that for about 2 days on and off. Water at first looked like a rust milk shake. Now it runs clear, even after I prod a lot with the copper stiffie. The cylinder steel walls look like new. Still no joy with the rear drain plug. Not a drop out of there.

So I put the water pump back on to close the hole, and mixed up a cocktail of 1qt degreaser and 1qt Lime Away. That got hot and boiled up pretty good. Poured it in and it has been sitting there for a couple days. Still no joy on the rear drain.

I think I may try the speedo wire/sleeve trick with a drill. Have drill, no speedo. Maybe some cable and a piece of copper tubing.

Once I get a little hole opened up, I'm concerned that that all I will end up with is a small hole and still a lot of gunk. Considering going a little more radical with muriatic acid. I think once I get done with the acid, assuming it works, I need to run some baking soda thru the system to neutralize the acid left on the metal walls. But I have to find joy first.

This is a lota work for water constipation. Any suggestions for this working in the dark?

The gunk is very likely stop leak which Farmer Bob kept a putting in the radiator so he wouldn't have to sell a kid or two for enough money for a new brass radiator. VERY common occurrence in these old engines.
You probably won't find anything that will dissolve it. Mechanical means is the only thing that will break that stuff up to get it out.
It is a tedious enough job to accomplish with a bare block. With a bare block you can use a stiff steel rod down through little coolant holes in the top of the deck to reach quite a bit of it at the bottom water jacket. Water pump off and freeze plugs out helps quite a bit too.

It's major surgery time- - - -pull the intake and exhaust manifolds, and pry the freeze plugs out. That gives you better access to the bottom of the water jacket so you can poke, probe, and pry at the crud that's accumulated in there. Mix up a STRONG solution of Trisodium Phosphate and water and heat it to almost boiling. It's what I use to degrease firearms prior to doing a hot salts bluing job. Pour the solution into the block to the level of the bottom of the freeze plug openings. TSP is "concrete cleaner"- - - -industrial strength detergent. You can buy it at big box hardware stores like Home Depot. It will soften non-rust debris that acid won't touch. Use a turkey baster or a suction gun to siphon the TSP solution out of the engine and reheat it when it cools down- - - -it can be reused several times. Good luck!
Jerry

I found joy. Without tearing the engine apart. Thanks for all the suggestions.

After cleaning all the major points around the cylinder walls and got clean water running thru. The drain remained.

I took a 1/8" steel cable and cut it to about 18" in length. Put about 2" of shrink wrap around one end. Cut a 12" piece of 3/8 copper tubing and put the cable thru it. Put the shrink wrap end into my drill. Running the drill backward (CCW), the cable stays intact. Running it forward (CW), the cable begins to splay out like a wire brush.

After a little prodding and wiggling in the drain hole with the cable running mid speed, got a little hole up into the block. A few drops came out. Then reversed the drill (CW) and essentially made a steel brush out of it. The gunk came out like a deer in church. Ran that wire brush in/out for about 10 minutes. Then hooked up a water hose to the drain and got quite a bit of gunk out of the water pump hole.

Hooked up a lever action drain valve as shown in the picture. Also drilled a small hole in the new thermostat.

Nailed everything back together, filled her up and ran the engine. Water flowed clear, drain drained clear and fast. Me be a happy camper.

I appreciate all the good advice. Couldn't have done it without it.

Looks like a winner! It might be a good idea to run the TSP solution in the cooling system for a few minutes to degrease the entire water jacket, then flush with clear water for a while. The oldtime heavy duty cooling system cleaners were a combination of Phosphoric acid to dissolve rust, and TSP to cut greasy deposits. The 2-part DuPont cooling system cleaner in the double-ended cardboard tube had an acid/degreaser in one end, and a baking soda neutralizer in the other. I haven't seen that stuff in years, but the chemicals it contained are still available.
Jerry

Good idea. I have a jar of Phosphoric acid I can dilute down to get the last rust turds. Will use some baking soda after that to base it back to neutral PH. I don't have the new radiator on yet as I haven't built the bracket for it, so I'm running a quick and dirty short circuit with clear flex line. Good for a few minutes and to use while I'm designing.

Any suggestions on what to use in the interim while the engine is empty of water to keep it from rusting (until I get the radiator on)? I could wait until I'm ready to hook up the radiator and do the TSP treatment last thing.

Think I may use Distilled water with anti-freeze too.

Just drain the cooling system and reattach the bypass hoses you've been running the engine with. Rust won't be a problem for quite some time- - - -at least a week or two.
Jerry