Fresh 461 leaking coolant
 

Fired my 461 up over the weekend and it ran great no issues. I started it last night and pulled it out into the driveway and noticed a decent coolant leak, after inspection it was leaking at the coolant hose at the back of the head. I tightened that up and it seemed to stop but after firing it up to pull it back in the garage it has a slow steady drip off the back of the oil pan from the belhousing area. I can't see anything up there but its definitely not coming from the front of the engine and the top now seems dry, what are the chances the machine shop that installed the rear freezeplugs didnt seal them properly?I'm going to drain the coolant tonight and reseal both the drivers rear bypass plug and the passenger hose nipple just to be sure they arent the problem. If its still leaking im going to drain the oil and check it for coolant. I'm praying I can just pull the trans if the plug is leaking and replace in car as this thing was horrible to install. Kauffman highports on it as well so no head plugs.

Only twice did i have multiple freeseplug leaks on a fresh build. Prior builds left the plugs in for the win.

1 jar of Barrs stop leak solved the freezeplug leaks, on both leaky builds, forever.

All new brass plugs from butler installed by the machine shop. If I try bars leak will that damage my new radiator and anything else on the cooling system?

It won't damage your radiator, try that first and if it doesn't work start trying to find the leaky FP. Hopefully it's not a rear plug.

Don’t assume anything about where it’s coming from!
Go rent or borrow or buy a radiator pressure tester before you start to gum up a fresh motor and rad with that stuff, or any other stop leak type stuff.

Confirm where the leak is first if you can!

Fresh 461 leaking coolant
 

I had a fresh build do that once and it turned out to be core plug on rear of engine block that required transmission removal to get to. The machine shop had slightly gouged block getting old core plug out and hadn't smoothed surface before installing new plug.

Agree with this. I'm not fan of using the stop-leak stuff in vehicles that I actually care about. I know some automakers use it from the factory even, but that's because they are just trying to save every penny possible and avoid warranty service repair.

It stinks because everything is brand new, I'm definitely going to try replacing it in car if its a rear plug. I cut the ears off the th400 so I can sneek it past the headers. Hopefully its the rear nipple and head plug. Going to reseal them first

Hopefully you will get lucky and the rear 1/2” pipe thread hose nipple will just need a redo of the pipe tape that should be on it.

Tape? As in "Teflon (PTFE) sealing tape"?

Works great for homeowners sealing natural gas connections that stay screwed-together for decades. Has no business on an engine; although coolant systems would be better than oiling systems.

Consider an anaerobic thread-sealing paste such as Loctite 592, or similar (565, 567, and the chapstick-like semi-solid, and there are other variations as well.)

Pipe thread sealer that hardens like threadlocker.

https://www.amazon.com/dp/B0002KKTH2...v_ov_lig_dp_it

55 years of twisting wrenches here, put a can of Bars Leaks in it and be done with it. This is what I prefer to use for leaks such as you have.

https://barsleaks.com/product/pellet...op-leak-plt11/

It will have zero effects on the cooling system if used as per directions, I have it in 3 of my own cars, and trucks, it works just as described by the manufacturer.

Over the years I've worked at a good many dealerships, and we used it on new cars frequently. GM sells the cooling system pellets in the parts network, and it is made by Bars Leaks, for GM.

https://barsleaks.com/product/radiat...k-tablets-hdc/

I've used the GM style Pellets, as well as the heavy duty pelletizer sealer that I linked to in probably hundreds of cars, with no ill effects. Just follow the manufactures directions. For they type of leak you're describing I would used the Heavy Duty pelletized sealer.

If you have hard water, I would suggest using distilled water to top off the system, it does make a difference over years if the coolant isn't drained and flushed regularly. BTW no need to drain the cooling system after the repair seals, I leave it in to head off other minor leaks in the future.

Decades ago I owned an 81 Bonneville 5.7 diesel that was losing coolant from the head gasket seepage, very common during the 80s GM diesel run. I put a can of the pelletized sealer in it to not have to deal with a head gasket, and bolt replacement update that the diesels were famous for in my own car. I owned the car for at least 5 more years after adding the Bars Leaks into it, and it never lost any more coolant in the 5 plus years I owned it. It didn't plug up the radiator, nor did it cut any heat from the heater core. It worked just as it is described by the manufacturer. It made a believer out of me that it was a permanent repair, and it didn't impair the cooling system over years.

One other thing I have found over the years is the heater hose you're dealing with can rupture internally due to the tight kink they operate with, and won't leak until they heat, up and the system pressurizes. Then the will sometimes leak a pinhole spurt. For what it takes to put a new hose on, you might try that first if it's not a new hose.

:2cents:

Thanks for all the replies, super helpful all the way around. I did use tedlon tape originally but will be switching to a thread sealer tonight. Fingers crossed that's what it is. I'm not opposed to used a leak sealer if its a rear plug

FWIW, if the sealer was a problem, then they would incur more warranty cost from using it. There are 2 pellets put into the cooling system when the car is new at the factory, just to head off any new car minor leaks. GM starts the cars out with sealer when new......;)

They've been doing this for decades, and all the major car manufactures use them.

Does it work 100% of the time? Well take it from someone that worked in a good many dealerships, no it doesn't stop all leaks. While working in a Buick dealership I changed dozens of head gaskets over 3 years that I worked there. We did try sealer before we pulled cylinder heads though. If it didn't work, then you had to bite the bullet and put head gaskets on.

BTW, it paid 4.6 hours to do a RWD Buick V6 under warranty. A good many weeks I took home less than 40 hours of pay due to those V6 Buick head gasket problems.

There were 6 gasket revisions back in the early 80s due to engineering screw ups in Buick V6s, and they cost me a ton of money. The worst case scenario, was having 2 stalls, with a head gasket job in them both........:mad:

I have used chemical coolant-system sealers. K-W Permanent Metallic sealer has kept my Olds 455 from peeing it's coolant for about ten years now, maybe more. (Porous weld repair to the cylinder head.)

On the whole, they're not my first choice. A core plug may leak because it wasn't installed properly. You seal the leak, the system pressurizes...and the core plug blows-out. Or it may have a pinhole actually leaking, but is severely corroded on the back side. You seal the leak, the system develops pressure...and the core plug ruptures.

The same sort of thing can happen with other cooling system parts--failing radiators, failing heater cores, failing coolant tubes, failing head or intake-manifold gaskets. You seal the leak, and cause a catastrophic failure later.

Given a choice, I'd prefer to identify the true cause of the leak, and FIX it, rather than dropping sealer in the system. A sealer may be appropriate, but only when you know why the thing is leaking to begin with.

I remember those GM sealing pellets and used them on the Cadillac 4.1 L engines in the 80's. These engines were notorious for having intake manifold gasket leaks because of the aluminum intake and cast-iron blocks. They worked great and the comment about GM using them because they didn't want warranty repairs doesn't wash! The pellets worked well and kept the gaskets intact. Further, distilled water in the coolant system is a must!! I use it in my classic and was told by an established radiator shop that if you don't drain the coolant much, distilled water is the best way to go.

I used Alumaseal years ago and it worked well. It is still made and comes in a small plastic tube.

The piece-of-crap 4.1L and it's later derivatives were built like the Vega 2.3L engine. Aluminum block, cast-iron heads.

The blocks were so flimsy that they were difficult to remachine. The stress of the machining operation was enough to distort the block; which then made the machining imprecise.

Make sure the heater hose/heater core is not leaking and dripping water to the back of the block when the failure was the heater core.
I have seen that multiple times on peoples vehicles. Also do the heater core restrictor mod if you have to replace the heater core.

Tom V.

For 51 years I have purposely used Teflon tape on pipe plugs / pipe thread fittings ( as seen here ) that thread into aluminum.

When done correctly there is never a leak.
Use whatever the the hell you care to, but don’t degrade something thing that works when it clearly does, and in fact time after time it does so!

Just resealed the nipple and plug with permatex thread sealant and im putting it back together. I bypassed the heater core as I'm not using one for now, I have the hose running back to the water pump. Hopefully this does the trick, will know in just a bit.