Newly built engine is leaking coolant and I'm stumped

[73MustangCoupe]

The 351C motor I built for the Rickster has been installed, transmission is in, exhaust is in, and fuel system plumbing is done. I've checked the fuel system for leaks, but have no fuel in the tank yet. I was hoping to start the engine for the first time this weekend. I filled it with coolant and was finishing up some wiring that I needed to do before firing it up. The next morning when I put the car in the air, I found a small amount of fluid on the floor below the bell housing. I removed the inspection plate and found a small drip about to come out. I pulled the valve covers and all is oily, but otherwise dry up there. I can find no leaking freeze plugs or pipe plugs, and no leaking hoses. So, where is the coolant coming from? Close inspection revealed some around the separator plate along the rear oil pan seal. I don't recall any openings to the water jacket inside the bellhousing, just oil gallery plugs and cam tunnel plug.

Sooo.... I am stumped. I have no idea where the coolant is coming from, but I'm thinking it shouldn't be leaking. If you have any ideas, insights, or suggestions, I'd sure appreciate hearing them. Thanks.

 

[boilermaster]

73mustangcoup.
pipe sealant on the block drains and both tight ?
coolant could be leaking from there to the oil pan rail to the separator plate.
With the engine installed, it is all downhill.
same can be said for any of the freeze plugs.
I have seen coolant take some pretty weird paths, almost defying gravity, especially on a freshly painted engine.
Boilermaster

 

[Ron Tanzi]

I hope it is not one of the head gaskets. Since you have not run the engine yet, suggesting that you add tracer dye is a non-starter. If you have a cooling system pressure tester or access to one that would be my next move. Having a coolant leak being at the back of the engine is a little weird. God speed.

Ron

 

[timachone]

Perhaps the clamps of the hoses to the heater core are not tight enough? I have also a small dripping since my engine was rebuilt and never been driven and suspected a leaking, fresh head gasket. It drove me nuts. Then one day I traced the drips once more and it went from the in and outlet of the heater core. But the paths the coolant took were really weird and not very reasonable the first few views...

Just my 2 cents to this topic. So prove other things first, often it's the more easy ones...

 

[Hemikiller]

The bellhousing area of the 351C is "dry", with no core plugs. The plugs present are for the cam tunnel and lifter oil galleys. I would borrow a coolant pressure tester as suggested and see what you find. Hopefully it's a leaking core plug or water pump gasket. If not, this leaves you with two options, head gasket leak or a cracked head or block.

 

[73MustangCoupe]

Thanks, guys.
Bentworker. All the block drains were installed with sealant and are dry. I also checked all the freeze plugs, and they are dry.

Ron Tanzi, pressure testing was my next step. I was thinking of adding UV dye to the coolant to make any leak more visible. You said since the engine hasn't run, the dye is a non-starter. Why?

Tim, I double checked the heater hoses and they are dry. The heater core is new, and was under pressure when I pulled the plugs to install the hoses, so I know it's good.

Hemikiller, I appreciate your suggestions. I had the block magnafluxed when at the machine shop, but I later heard horror stories about them, and they are now permanently closed. The cylinder heads are new, from Trickflow, so I doubt they are the problem. I think I will pull the transmission, flywheel and separator plate, pressurize the cooling system and see if I can find the leak. I am hoping for a head gasket, but I am pretty anal when putting a motor together, and don't see how I could have messed that up. I am really worried about a hairline crack in the back of the block that the machine shop missed.

I do have another Cleveland block with a pair of 4V close chambered heads that I got for another project, but I really hope I don't have to use it. Fingers crossed for a head gasket (although I don't see how coolant would have made it down to the bottom of the block without me finding it.)

I'll let y'all know what I find.

 

[boilermaster]

73musstangcoup,
Possible porous spot in the engine block casting?

 

[Ron Tanzi]

Thanks, guys.
Bentworker. All the block drains were installed with sealant and are dry. I also checked all the freeze plugs, and they are dry.

Ron Tanzi, pressure testing was my next step. I was thinking of adding UV dye to the coolant to make any leak more visible. You said since the engine hasn't run, the dye is a non-starter. Why?

Tim, I double checked the heater hoses and they are dry. The heater core is new, and was under pressure when I pulled the plugs to install the hoses, so I know it's good.

Hemikiller, I appreciate your suggestions. I had the block magnafluxed when at the machine shop, but I later heard horror stories about them, and they are now permanently closed. The cylinder heads are new, from Trickflow, so I doubt they are the problem. I think I will pull the transmission, flywheel and separator plate, pressurize the cooling system and see if I can find the leak. I am hoping for a head gasket, but I am pretty anal when putting a motor together, and don't see how I could have messed that up. I am really worried about a hairline crack in the back of the block that the machine shop missed.

I do have another Cleveland block with a pair of 4V close chambered heads that I got for another project, but I really hope I don't have to use it. Fingers crossed for a head gasket (although I don't see how coolant would have made it down to the bottom of the block without me finding it.)

I'll let y'all know what I find.

On my comment on not using the tracer dye in the cooling system without running the engine: I don' t think the dye will mix well enough with coolant that is already in the engine. An option I thought of was draining out as much coolant as you can and then mixing the dye and coolant. Then pour the dye treated coolant back into the engine. You may not really need the dye since you can get eyes on the back of the engine, the leak may be obvious when pressurized.

Ron

 

[Sheriff41]

73musstangcoup,
Possible porous spot in the engine block casting?

This happened on my 69 Boss 302 back in the early 80s. Actually, it had a crack on the back of the block. Being young and poor, I cleaned it as best I could and patched it with JB Weld. It was fine for years in the AZ heat! Not sure how it would hold under freezing conditions, though.

 

[giantpune]

What type of intake is on the motor? I was thinking if your water neck on the front of the motor is not sealing up, water could be leaking out and then running towards the back up under or around your intake manifold.

Next guesses have already been stated. Head gasket not sealing up or a cracked block.

One diagnostic test is the same as when you have a leaky swimming pool. Water seeks its own level. Let it leak and pay attention to what the height is when it stops. That may give you an idea where to look.

 

[73MustangCoupe]

The coolant level in the radiator hasn't gone down significantly. It's down less than 1/8".

I did drop the transmission. What a pain in the backside. The torque convertor did not want to separate from the flexplate. It took the better part of a day to get the flexplate and torque convertor apart so I could get the flexplate off and check out the back of the block.





There is coolant around the oil pan seal extending up along the pass side.
Tomorrow, I will drain the coolant and mix in some UV dye, refill the system and pressurize it to find the source.

Anyway, that's what I've found. I'll let you know what else I find over the next couple days.

 

[boilermaster]

73Mustangcoup.
Definitely a strange place to see coolant.
At this point, I wouldn't even rule out a timing cover leak running down the full length of that oil pan rail.
Boilermaster

 

[Sheriff41]

I know you may have already checked this but is there coolant in the oil pan? If you have oil in the engine coolant leaking internally and into the oil pan would make the oil level show overfilled on the dip stick. That coolant is going somewhere.

 

[73MustangCoupe]

I haven't even gotten to add oil to it yet. That was next, but the coolant leak sidetracked me. I did remove the oil drain plug, but nothing there but a few drops of oil - no coolant. The coolant leak is very slow, but does drip, like 1 or 2 drops every hour.

And yes, Boilermaster, I am going to look at the timing cover and water neck, as well. I had a difficult time getting the water neck gasket to seal, but I can't find any leaks up there now.

I will let you know what I find.

 

[giantpune]

I would take a napkin and tear off little bits of it and cram them everywhere the coolant may be running on the outside of the engine. Like make a little ball and stuff on each side between the block and the oil pan. And stuff some around the water neck. Steal some flour from the kitchen and dust the back side of the engine. Then come back in a couple hours and see if any of them have gotten wet.

 

[vintageman]

I would take a napkin and tear off little bits of it and cram them everywhere the coolant may be running on the outside of the engine. Like make a little ball and stuff on each side between the block and the oil pan. And stuff some around the water neck. Steal some flour from the kitchen and dust the back side of the engine. Then come back in a couple hours and see if any of them have gotten wet.

Good advice, unfortunately, I have been forced to do that on other cars, luckily, not on my recent build.

Tom

 

[73MustangCoupe]

Hey Giantpune, that's a really good idea. Not exactly what I did, but kind of.

I ran to O'Reilly's and picked up some UV coolant dye and black light. I drained the cooling system into a 5 gal bucket, added the dye, and then refilled the radiator. I also got a radiator pressure tester and pressurized the system. The pressure dropped slowly, and I found a tiny leak around the upper radiator hose at the water neck - a few twists on the hose clamp stopped it. I pumped the pressure back up, and found coolant leaking along the passenger side of the oil pan gasket.

I used some bits of paper towel to find that it was coming from the area behind the motor mount. I can't tell for sure, but I think it's seeping from the freeze plug.

Tomorrow, I will pull the headers off that side, and use the engine hoist to lift it enough to remove the motor mount and inspect the freeze plug and surrounding area.

So that's what I found, so far.

 

[will e]

A freeze plug, while a pain in the butt, would be a better case scenario than some of the ideas so far.

 

[71ProjectJunk]

A freeze plug, while a pain in the butt, would be a better case scenario than some of the ideas so far.

You can say that again!

 

[giantpune]

A freeze plug, while a pain in the butt, would be a better case scenario than some of the ideas so far.

Back when i was about 17, i had a 84 buick regal. That thing rode so smooth. It was like you were flying.
One day it started having engine trouble, overheating, dieseling, and all that. I didn't know anything about fixing cars at the time. Ended up up selling it to a guy for $300. He got in there and replaced a $0.50 freeze plug and the car ran great.