4.3 using anitfreeze

[big zeke]

I have a ~1993 4.3l 4bbl with Alpha 1 leg, the engine is close loop cooled (block is full of glycol mix, heat is exchanged with sea water in a small HX) . The engine does not have a serial number (I have checked everywhere and had a few mechanics look as well). The engine was rebuilt a few years ago and since has had about 50 total hrs on it, during the rebuild, the block was magnafluxed and no cracks found in it or the heads. Recently it has started using some antifreeze, the last 5 trips it has consumed a total of about 5 oz, perhaps a bit more. The engine smokes visibly right when started up for about 30 secs and after a long run (say 30 mins @ 3400 rpm) for maybe 1 minute or so, no smoke otherwise. No funny noises, no loss of performance but the smoke smells of glycol.

Obviously there is a leak into one or more combustion chamber but is there any way (without tearing the engine apart) to tell if it's just a gasket (either head or intake manifold) or a more serious crack in the block. The glycol has always been kept up and is good to -37c, this block never froze.

I was planning to pressurize the glycol side with an automotive pressure pump (can put out ~ 10 psi) and then pull the plugs and look into each cylinder with a boroscope for liquid...does this seem reasonable or is there an easier way to figure out which cylinder is the culprit.

I've stopped using the boat until I can figure this one out...I don't need to test if this engine can compress antifreeze.

Big Zeke

 

[achris]

Re: 4.3 using anitfreeze

Hi Zeke,

Yeah, I remember the serial number saga :facepalm:

A few places you could be losing coolant. The one I'd look at first is the exhaust elbow/manifold gaskets (assumes the closed cooling system also includes the manifolds, of course)...

The other place to look is the weep hole in the bottom of the water pump. If the seal leaks, green stuff runs down the front of the engine...

Chris.....

 

[big zeke]

Re: 4.3 using anitfreeze

Thanks for the quick response. With your 2 suggestions, would either one put antifreeze into the combustion chamber? With your first suggestion do you think the exhaust would be hot enough right at startup to burn glycol? I'd think the exhaust would be cool until at least the cylinder warms up.

I am certain the antifreeze is getting burnt as the smoke stinks of glycol, when the smoke stops, the smell stops as well. One fella did suggest putting a bottle of "Bars Leaks" into the glycol but I think this stuff is suited for a radiator system (if anything) so I resisted the temptation. I'm a bit freaked out if it's a crack as the rebuild is largely a throw away is I'll be looking for a good donor block.

This thing is starting to resemble a money pit

 

[achris]

Re: 4.3 using anitfreeze

BOAT = Break Out Another Thousand... :facepalm:

Leaking exhaust elbow gasket would drop glycol in the combustion chambers...
A block crack would drop the glycol into the engine oil....

Chris..

 

[tpenfield]

Re: 4.3 using anitfreeze

Another thought regarding the pressurization of the cooling system . . . if you drain the system and then apply compressed air (10 psi), then you will hear air escaping where there is a leak. That may be an easier process that using a boroscope, etc.

Are the exhaust manifolds cooled by the closed system or just the engine block?

 

[big zeke]

Re: 4.3 using anitfreeze

Ya, I wasn't sure if hearing the leak will be easier than seeing the liquid. In either case I'll be draining the block I guess. The exh manifolds are cooled with glycol (similar to jackets water cooling in the block). In the closed loop, the heated water from downstream on the HX (this can be fairly hot) dumps into the exhaust elbows to quench the exhaust flow and then out the Y pipe to the lake. In an open system, lake water cools the exh manifolds and then flows up the elbows to the exhaust flow, the closed system has some blocking plates that shut this off otherwise the glycol would be pumped out of the block pretty fast.

I'll check the elbows, still not convinced on this one but it would be very good news if it is.

 

[bonzoscott]

Re: 4.3 using anitfreeze

Compression test? Head gasket?

 

[big zeke]

Re: 4.3 using anitfreeze

Ya, was hoping to figure out if it's a gasket (ie cheap fix I can do myself) or a crack (buying a new block, crabby for days). I'm settled if it is a gasket it would be either head or intake, there is no glycol leaking from the engine...it's all going out the exhaust. I can't see it being the exh elbows as on a closed loop system the glycol would have to get past 2 block off gaskets and a thin steel plate located between the manifold and the elbow.

Will start pulling the engine in the next few weeks...my boating is probably done this yr