I've developed a strange coolant leak around the passenger side motor mount. It's not a fast leak - maybe a pint or two over a week's time. I've checked for rusted freeze plugs, blown head gaskets (exhaust gas in coolant check) and leaks around the water outlet, t-stat, etc. The top of the motor is dry as is the front near the water pump. The drip runs from behind the lower engine mount bolts, down the brace / bracket to the starter and transmission. I've searched the forum for similar issues but have run into a wall.

Aside from pulling the motor mount to look behind, is there anything back there prone to leaking? I doubt the block is cracked as there would be oil everywhere too. Engine oil is black and clean - confirmed by an oil change today.

Any suggestions on what's causing this issue? I'll post up pics of the leaking area, top of the motor, etc, later to help figure this one out.

 

there may be a frost plug in the back of the head i know alot of motor's have them..just cant recall on the 5.9

 

a freeze plug usually rusts out from the inside. On the outside, it looks fine. On the inside, the plug gets eaten away until it leaks.

I had one fail behind the driver's side motor mount in just that way.

 

Ok.... Thanks for confirming there's one back there and it's failed you before. This is going to be a pain in the *** to fix but better than the alternative.

What size freeze plug is behind the driver's side motor mount?

 

put in a bottle of stop leak and cross your fingers.

 

Don't want to put a band-aid on the problem - want to fix it. The motor mount's shot so it's got to come off anyway so I'll replace it when I'm in there.

 

Can't recall the exact size. I'm sure you can cross reference on a number of parts sites. Go for brass plugs if you are keeping it for a bit.

 

Finally got around to tackling this one. Went to the dealer and picked up the larger freeze plug (1 5/8 IIRC) and went to replacing it. What I found made me cuss the previous owner.

He had obviously used Bars in the engine to fix the leak....but the plug was so badly rusted out the Bars had formed a barrier between the freeze plug, the motor mount and part of the block. After running cooling system cleaner for nearly a week the blockage was eaten away from the inside out resulting in the leak.

The freeze plug was so brittle it came out in two pieces.... With this leak source fixed, I am waiting for the next. I have seen a minor leak from the water pump / bypass hose area but it's intermittent. Must be the rest of the Bars leak....

 

I to have just found a leak from behind the mount. I would have to remove the mount to fix it. Is there a plug there? I cant find my repair book..

 

Yep, there is a freeze plug behind that motor mount. I had to change mine as well. It took about an hour.