Mysterious coolant Leak

I have noticed a very small coolant leak since I pulled my oil pan and have the nose of my car in the air. Engine is a 400 based stroker, oil pan is off the motor...

I have noticed a few drops of coolant per day on the ground right under the pass side rear of the motor (under the rear main seal retainer). I cannot seem to find where this is coming from.

I checked the freeze plugs, heater hoses at firewall, at valve, heater box drain, and water pump housing. When I drained the oil and dropped the pan, there was no sign of antifreeze in the oil.

Anything I am missing? There are no plugs on the back of the motor where coolant could leak, right?

Any ideas of what else I could check??

Maybe exhaust manifold stud/bolt leaking and running down.

Forgot to mention...this motor has Eddy RPM heads. I seem to recall those not being wet bolts.

You might use this "tank valve" which is less than $3 at O'reillys. screw it into the 1/8 NPT coolant temp sensor & add some psi from your air chuck & grab your tire psi gauge & pump in 5 or 10 psi. use short blips with the air chuck cuz you can reach a critical psi quick & blow out some coolant hoses real quick (it ain't like airing up a tire). it'll make the leak leak

Head gasket, I had one that squirted a thin stream under pressure. I used the pump up tool on the radiator, almost 20 psi before I found it. Blue gel-pro gasket, almost new

This leak is from an engine sitting for three weeks with no oil pan. I can't imagine a blown head gasket would leak like this...especially since I saw no white smoke or lost any appreciable amount of coolant before I tore it down.

So you want to dispute the suggestion ???

Looking a bare block you don't have many other sources other than a head gasket or bolt.

It's doubtful an exhaust or head bolt leak would find it's way to the center of the motor.
So that leaves intake bolt (if drilled through), a head gasket, or the heater A/c system.

Is the back of the block inside the floor tunnel or in front of it. I might suggest laying under the car and looking straight up to see if their is any coolant hoses, heater /ac box etc. directly above the area of the drip. Leaks typically do not go sideways but rather straight down that is assuming they haven't a ledge or lip to follow.

Another thing to keep in mind, with the car sitting with the front raised up, the heater core, valves, hose connections are under more head pressure. HMMM
Or one could put a camera on it and possibly record the event and capture the source

Myself I agree with the previously suggestion(s) time for a pressure check

Wh haven’t you pressure checked it?
Dougy

Freeze plug in the back of block, behind flex plate ?

It wasn’t ‘blown’ it was coming straight out the front from the little hole in the lower corner. Defect in the gasket is the only thing I can figure

None there

Well I got a pressure test kit from a buddy and we pumped the system up to 18 psi. Aside from my lower hose leaking a bit, we were able to replicate the leak coming from the number 8 cylinder - a small drop on the piston skirt. The leak can't be that bad as once the lower hose bled down to about 15 psi, it stopped leaking and the system held pressure.

I was then thinking, maybe head gasket, so I pulled the number eight spark plug and expecting a burst of coolant, I got nothing. Plug looks good. I used my handy borescope and inspected the cylinder. From what we can tell, I might have a casting defect where some of the coolant is weeping through the cylinder wall about an inch below the head gasket. If you look at the pictures you can see the little droplets of coolant on the cylinder wall - but they are all well below the head gasket. We ran the scope around the top of the cylinder/gasket and saw no sings of moisture.

So the verdict is - very small leak through the cylinder wall in the number 8 cylinder.

Since I likely have had this likely going on for years and it isn't diluting the oil from what I can tell (after 2 years/2000 miles), I am going to run it as-is with the plans that eventually I will need to pull the motor and get it re-sleeved.

Not good. I would run these. Stop Leak

there is a blue bottle of stuff called K-Seal. that stuff seems to work pretty good, and might work for what you are doing.
the "roadkill" guys used a few bottles of this stuff to seal up a smoking head gasket on one of their episodes, and it stopped their severe leak [along with a new radiator cap]
of course they beat on the car severely, which i don't think you are going [or planning] to do.
you might want to try some of that stuff. sorry i don't have a link.

The Bars leak pellets work extremely well. GM had a bulletin on using them because of casting porosity issues. I had a pair of ported iron heads that magnafluxing showed cracks and the did leak. I would use the bars leak pellets and the leak would stop and we would race all season. My cracks were in the exhaust ports so no problems in that area. However the poster here should try to see how far up the leak is. If it gets by the rings when the piston is down it is just a time bomb as the cylinder pressures being high may not let the stuff seal. I would use them as a precaution as you do not want coolant in the oil.

"milkshake" is NOT good for sure !

I ordered some of that "K-Seal" and we will see if that helps. The oil in the pan was 2 years old/2000 miles and looked like well-used oil (no milkshake) so I am hoping I have some time to decide what to do for the longer term.

Frankly, that would make me nuts, just waiting for the problem to get catastrophic.
Had a buddy that ran his 351C drag motor a whole season, though, pouring Bars Leaks into the thing until it clogged his radiator.
Looks like there's already a rust ring forming, if I'm analyzing that bore photo correctly, so it's pumping coolant into the bore.

flush it out real good and use water only... get the temp up to 200 or a little higher like its about to overheat. the reason to do that is it will open the crack real good. if it stops the leak, it will prob. never leak again unless you get it hotter than when you made this repair. there are many products with many issues. this works really well and last. Buy this ! https://www.jegs.com/i/Moroso/710/3...=4579878248437694&utm_content=Moroso

It says not to use with antifreeze, I’m guessing water on first application, once it’s sealed use the mix?

If that pin hole turns to a crack and hydraulics it’s not going to be pretty.
Doug

Water in the oil is not good, but antifreeze in the oil = a dead motor very quickly.
I assume you are pressure testing your cooling system while its still cold and have found a minor leak. Once the motor starts heating up, about 1/2 way to operating temp, I've seen a lot of coolant leaks get worse, but then they close up when the motor gets up to temp.
If you are unsure if your coolant leak is block related, drain the antifreeze out of it and fill it with water until the block has been sealed again. Gene

Bummer

yes . . antifreeze interferes with the cure of ceramic seal. after you get it sealed and you know you have stopped the leak, you can run all the antifreeze you like ! get it good and hot -not ring killing hot just try to hit 220 .. i always run fresh water in and keep it coming out [flush it w/ engine running no t- stat ]until its very clean. then close it up and then run it with only water and ceramic seal until its up to 200-215 .

So this isn't a race motor - it's a street car. I read the data sheet on this stuff and it says pretty clearly to run pure water only once it's used. I would prefer not to have to do that.

What about the antifreeze friendly stuff? Moroso All Weather Seal 35520

Here is the instructions. They read like this is for race motors only and you have to run pure water for life after you treat the motor. Am I misinterpreting this?

Use the pellets in the link I have above. They work well with antifreeze and are the same that GM used. They work.

I had a similar issue with a 440. I'd see leakage when cold but it would stop when warmed up. Turned out to be the block. Not cracked just leaking thru the casting where the numbers were cast. Turns out to be a common issue w/ late model big blocks. I ran some sealer, not sure the brand and never had an issue again,

ceramic seal will work fine after its cured, with antifreeze...... heres another brands same product... scroll to the bottom. read the last sentence .. http://irontite.com/ceramicmotorseal/

I ordered the Ironside Ceramic Seal and their flush. I may go that route as it seems more specific to my scenario.

I use to cut a peice of cardboard to put over radiator then get temp as said to almost overheat condtion . I had a 440 with no issues until I blew a hose one day and overheated. Then I had to repeat the process with great sucess. My opinion is you dont need much stop leak (I used Porter seal) to fix it . Dont fill your motor with to much pellets JMO

Looks like I'm way old school. I dont think they sell it anymore. Check out the instruction though.
https://www.ebay.com/itm/Vintage-Au...iator-Cracked-Block-Sealer-/382889085181

Update for everyone:

- I drained the coolant this morning. Been in the motor for just under 3 years and it looked fine. Very little sediment/rust and no oil in it.
- I refilled with tap water only and took a drive. No issues.

When the IronTite kit comes in, I will do the "flush" and then the ceramic seal (with distilled water). I will let you know how it turns out.

there are many products out there like the blue devil. it will do this job too. only problem is it can stop up other things. i never had any "issues " with this system .. there is not 1 way to do it. this is tried and true for me.. i am confident it will work very well for you ! let us know..

So I thought about this more and went ahead and pulled the T-Stat and reverse flushed the cooling system by blasting water through the t-stat neck out of the lower hose. I used a shop vac to then blew air the same way until it was pretty dry.

I didn't see anything besides watered down coolant come out - no sediment or gunk. Since this system seems pretty clean, should I bother with using a flush product at this point or go straight to the ceramic sealer? I am pretty confident that there is pretty close to zero anti-freeze left in the system and I had no issues with my heater core as far as lack of heat.

I am trying to avoid having to put the t-stat back together, running the car, then having to tear it down (while hot) to get the flush out completely so it doesn't sit in the system. Am I asking for more trouble using a flush product? Or should I just use it since I bought it?

What about leaving the t-stat out just for the flushing process so I can just pop the hose to flush? My car has AC so one of those housing bolts is a PITA to get on when the motor is nice and hot.

Listen to what NITROUSN has advised. These pellets are cheap, effective, will not clog heater cores and will do the trick. You do not have to drain the system, and you do not have to run without antifreeze when it's below freezing outside. GM specified these for use in the Northstar engines and others where porosity was an issue. I've use them countless times and usually keep some in stock at the shop.

We had a friend who had a suburban that would lose a half gallon of coolant a month for years. They spent thousands of dollars replacing this and that at the advice of three different mechanics. Nothing worked. They were about to get rid of it when they were over at the house and told the story. I asked if they wanted me to give it a shot. They agreed. I took off the radiator end of the top radiator hose, crushed up two of these pellets and put them in, topped off the coolant and drove it around for a half hour. They still have the vehicle to this day and have never had to add more coolant.

Certainly worth a try

---- > with the t stat out, remove the lower w/pump hose from the rad. . with the eng. running, keep your garden hose running inside the lower hose and it will flush it self out in a few minutes. the cleaner the better. then add your sealer ...