Got a leak!

[91chevyburbbeast]

Chevy 350 had a long standing coolant leak visible from back of motor near starter. What I’ve done: replaced I take manifold gasket, checked freeze plugs in back of motor. Despite what I’ve tried I can’t seem to find it. For a while my thermostat housing was leaking but I took care of that (months ago) but I still can’t seem to keep coolant in the truck. I am concerned that the head gasket may be leaking to the outside of the motor because that would just be a pain. Any other suggestions before I rip the top of my motor apart?

 

[Abusfullofnuns]

Other than heater core hoses, it sounds like you are on the right track. Could be a crack in the water jacket too, I suppose.

 

[91chevyburbbeast]

I think I’ll start with the hoses, if I do have to break in to the motor would you suggest doing a top end rebuild while I’m in there? It’s gout about 150,000 on it original from ‘91

 

[dyeager535]

Chevy 350 had a long standing coolant leak visible from back of motor near starter. What I’ve done: replaced I take manifold gasket, checked freeze plugs in back of motor. Despite what I’ve tried I can’t seem to find it. For a while my thermostat housing was leaking but I took care of that (months ago) but I still can’t seem to keep coolant in the truck. I am concerned that the head gasket may be leaking to the outside of the motor because that would just be a pain. Any other suggestions before I rip the top of my motor apart?

These can be frustrating, I know from experience. Bit of advice if you have a few dollars spare to throw around ($5?). You can get one of those "inspection cameras" on ebay that will hook up at least to a laptop, unsure about phone, and they are small enough you can get them in a spark plug hole. Not that I'm saying look there, but they aren't bulky at all. I ended up pulling my motor before testing the camera out for that purpose, but it does work. When you can't see some of the areas, like the rear of the engine, it's just a guessing game unfortunately.

 

[6872xtc]

Did you check the knock sensor closely?
That's the only suggestion that I have , besides what has already been posted.

 

[diesel4me]

I'd put a tube of that Aluma-seal powder or Copper-Seal and run it awhile--that stuff seals minor leaks well without any clogging..
If it still weeps after that then you've got bigger problems..
GM uses those rabbit poop pellets at the factory to ward off any minor leaks when the vehicles are new..

Some other things to check--most Chevy heads had a pipe plug in the rear on the passenger side,that port would be used for the temperature sending unit if the head was installed on the drivers side--it can leak..

There are two more freeze plugs behind the flywheel or flex plate..pray it isn't those!..

I've seen coolant drip out of the exhaust manifold bolts before too--usually that means a crack,or the bolt hole was drilled a bit too deep and hit a water jacket--but its usually not a major one,some sealant on the bolt threads usually stops it..that one is hard to diagnose because the coolant evaporates on the hot manifold while it is running,it only weeps a little after the engine is shut off..

 

[1-ton]

I would agree with taking a closer look at the thermostat housing area. I had a leak on my 350 in the same exact place as yours, and it was coming from the thermostat housing area. It is hard to see the leak from the thermo housing area because the spark control module, EGR control valve, their mounting plate, and alternator wire harness block the view of the coolant flowing down the right side intake manifold valley, and then down the back of your engine.

 

[brans87]

Rent a coolant pressure tester and apply pressure start looking!

 

[Snoots]

If yours has them, check the freeze plug in the back of the head.

 

[Blue85]

You know, after dealing with mouse vandals underhood, this kind of sounds like a feature.

 

[ChrisPerry]

Headbolts can leak coolant also. Pull, clean, seal, and retorque each one as needed. I like ARP thread sealant, but any high pressure paste style teflon thread sealant works.

 

[diesel4me]

I've seen coolant puddle up on the center intake manifold bolts on old small blocks often too,they pass thru a coolant passage..Indian Head Gasket Shellac on the threads seals them forever,but they may never come out again either..

As for the mice--my 6.2 has a pile of shelled nuts on its intake lately,and the thermostat housing weeps enough to leave some coolant on it--but I haven't seen any dead Mickey's yet..they are probably drinking it to catch a buzz..thankfully they have not chewed anything important,or moved into the cab...yet..