4.3vortec clunky cranking

[Gaetan Carrier]

Have a 4.3 vortec that started fine till recently. Batteries are fully charged but need a jump to barely turn engine over. Makes a loud clunking noise while starting but runs fine once running, 4000 rpm with plenty of power. Able to turn engine with breaker bar with plugs still in place. Oil looks brown and not milky but definitely discolored from being of season. Not sure if I need a starter, batteries or a new motor.

 

[Silvertip]

Re: 4.3vortec clunky cranking

If it is clanking only when cranking, then either the starter is loose on its mountings, the starter end bell is broken, a mounting bolt is broken, there is a broken flywheel or pinion tooth, a loose flywheel, to name just a few. If it needs a jump when you have a fully charged battery there is obviously something dragging. How do you know the battery is fully charged? Did you do a voltage test where you watch the volt meter while cranking the engine? If not -- try that. It may be the battery mesures 12 volts but when under load it falls on its face (as in bad cell or cells, or simply a tired battery). Do the gauges show normal oil pressure and temperature?

 

[Adirondack]

Re: 4.3vortec clunky cranking

Sounds more like hydrolocking to me. The discolored oil only adds to the suspicion. before restarting remove all the sparkplugs and see if it cranks easy, and if water comes out any of the plug holes. If so you have to find out how the water is getting into the engine. If all is ok, ignore this post, and carry on.

 

[squeak911]

Re: 4.3vortec clunky cranking

My exhaust manifold riser gaskets were leaking on my 4.3l. It would drain the water that was in the riser down into my cylinders.

 

[Philster]

Re: 4.3vortec clunky cranking

Have a 4.3 vortec that started fine till recently. Batteries are fully charged but need a jump to barely turn engine over. Makes a loud clunking noise while starting but runs fine once running, 4000 rpm with plenty of power. Able to turn engine with breaker bar with plugs still in place. Oil looks brown and not milky but definitely discolored from being of season. Not sure if I need a starter, batteries or a new motor.

Water. Brown oil = water in oil. Clunking = water in cylinders.

Yes... It'll run. Oil should be shiny brown when brand new and even after just a few hours should look black. Oils get black because they are great cleaners and suspend dirt well. Brown is bad. Clunking is bad. Both scream 'water!'

Suspects: leaky risers/manis, blown head gasket, cracked head, intake.

Yes, it will run... but the engine is likely corroded and down in compression or leaking combustion. That's partly why it'll run w/ water in it. Even though the water won't combust, it'll squeeze past rings and other weaknesses.

 

[Gaetan Carrier]

Re: 4.3vortec clunky cranking

You were all correct about water in the cylinders, exhaust ports in manifold were full of water. I'm picking up new "dry joint" gaskets that go either side of the 3" spacer for this "2004" vintage 4.3L. I'll be carefully cleaning up the surfaces of the castings with a file, any suggestions on a sealant to use in conjunction with the fancy metal/paper/rubber gasket?

The side of the engine with the problem has an after market exhaust manifold and it turns out the gaskets were installed incorrectly, with restricted holes on the inlet side. This side of the engine was running a bit hotter but the riser and manifold look clean, I suspect the restricted flow was causing the overheating condition?

Water has been drained, cylinders well oiled and fresh oil will be in the engine before starting. Any other words of wisdom towards salvaging this engine?

 

[Philster]

Re: 4.3vortec clunky cranking

Hmmm... it can be very hard to get all the water out. Also, check the valvetrain for the serious buildup of foamy oil. Can you pop open the inspection hole on the valve covers? I suspect it's whitish there.

I think you have some number amount of oil changes to make before you are in the clear. I hope you've fogged the engine or preserved the metals via something like fogging oil or Marvel Mystery Oil, which are nice protectants.

I can't make suggestions for the gaskets, but once you are clear of water, and the fix has been made, see how she performs and take it from there......