The Stovebolt Site Forums The Shop Area Engine Shop Build-up in water jacket and drain plug

I'm really glad that the Stovebolt forum is available with information and help. My 50 3100 wouldn't be on the road today if it wasn't for you folks.

I have a running 1957 235 engine (sitting on a cradle). I can't drain my coolant. There is some kind of hard black deposit blocking the hole behind my coolant drain plug. It has the consistency of packed graphite. I removed the freeze plugs so I could see inside the water jacket. There's the typical red rust (not bad) but only at the rear of the block (at the drain area) do I see this black deposit. It's a real pistol to get something inside to do cleaning (chipping).

1. Does anyone have an idea what this black stuff is? Carbon? Stop leak? Copper erosion from a radiator? I hope it's not crystallized oil which would mean I have a crack somewhere?

2. From the coolant drain hole to the water jacket, is there a direct path or does it turn left then go up? This would help me a lot to clean out the passage.


There is no water in the oil. Cylinder compression is 130 in #6 and 135 to 150 in the other cylinders. The engine runs fair and probably needs a carburetor kit.

I have no idea what the black stuff is but it is not uncommon for that area to be blocked as it is the low point. I almost always need to dig out the crud to drain these engines.

One of the many nice things about later 235/261 blocks is that there is a large hole in the block when you remove the water pump. I used thick copper wire to clear out a 261 block - it took a lot of effort and a lot of time. If you cannot use a copper wire to enter the block through the drain cock near the driver's side rear of the block, you've got problems. Coolant water must be able to circulate around the rear of the block. Keep at it.

I have had a few of these sixes and I don't think I have ever had one that would drain out of that hole.

Use a hand-cranked drill with about a 1/4" bit, and gently bore through the crud. The drain petcock hole is a 1/4" pipe thread, so drill bits up to about 3/8" can be inserted without damaging the threads. Just don't get after it with a power drill and bore a hole in a cylinder wall. Once the hole is opened up and flowing, stiff wire can be inserted to dislodge some of the crud.
Jerry

I very slowly drilled the drain hole till I touched the casting then stopped. No luck. It's still plugged up. I've taken a hard wire and picked out as much as I can. I picked a passage going left at the back of the drain hole but it stops after about a 1/2 inch. It feels like casting at that point. My guess is that the passage goes up to get to the water jacket but my pick will not go up that far because of the angles. I removed the water pump but I can't see to the back of the block. There is no way around #1 cylinder. I have to clean what I can from the rear freeze plug hole. I put a little of the black stuff in a plastic container and poured in a little muriatic acid. It does not react like metal (fizz and bubble).

dissolved passivied silt is what i call it. yeah i found this in all of my engines when i was told "just flush the block and youll be ok" NOT! first off to get the block to drain you need to remove the drain valve on the side of the block. then stick a 1/8" welding rod in there and if you have to pound it in go right ahead. while working the rod deeper and around it should start to weep. when it does its yours to take but it just may take some time. since you pulled the soft plugs and its on a cradle i would pull the head and once you get it off youll know why i said to do so.

like tim says the hole in the front from the water pump makes easy access. with the head off and the water pump out and you already took the soft plugs out youll be able to see whats in there and the progress you make removing the crap which there is more in there then you can fathom. start by getting a clear path from the drain plug all the way around #six cylinder and to the block wall on the side where the starter is for the chunks to flow out which youll most likely have to bust them up to fit out the hole. then carefully working the cooling passages in the block from the top down to the drain plug then work yourself systematically to the front of the block. careful not to make a mess and get it in the cylinders. i always put the piston up where i was working to keep any water from ending up where its not supposed to be. if you do take the head off make sure to rod out and blow out the cooling passages in the bottom side of the head. i made a gadget out of 1/8"id copper tubbing to fit on the end of a garden hose with a shutoff to use for flushing and flow conrol. after i did all this which was in preparation of a engine build, i filled the block up with XXX boiler cleaner and left it set for a week. i thought i had it cleaned from rodding HA! all i did was remove the top surface and chunks so that the boiler cleaner could get to the block and do its thing. flush many times. since the engine is where it is its a good time to do this.

with a clean block and a recored radiator the only time it goes above 190 is when im hauling a load home on a hot summer day with 4-5 tons of stone on the back of the dump with a 59-235 on a hill called the "blue mountain"

I bought a snake and drilled down into the deposit. It's a good 1/2 inch deep. Acid only softens the top layer. I took a sample of the deposit and burned it with a torch. It doesn't burn, just glows. Like 51 ashton says, it's got to be chipped out but I'm not ready to pull the head off yet. By the way, I'm still green and learning (the hard way). Apparently I didn't flush the block good enough before I first ran the engine. My radiator filled with enough sunflower seeds to grow a garden. Mice just love engine blocks. Luckily a back flush got it out.

Thanks to all for your help.