Back - flushing block & heads

[Alws55]

73 350 Chevy omc.... I've done everything from impeller to thermostat....flushed exhaust manifolds....so I believe the block & or heads are clogged....how about back-flusning the block....rather than taking the heads off & see what happens. Maybe tap on block as I'm flushing...any feedback?

 

[Bondo]

73 350 Chevy omc.... I've done everything from impeller to thermostat....flushed exhaust manifolds....so I believe the block & or heads are clogged....how about back-flusning the block....rather than taking the heads off & see what happens. Maybe tap on block as I'm flushing...any feedback?

Ayuh,.... Have ya pulled the drain plugs outa the block,..??

That's where the crud lays,....

 

[Alws55]

I neglected to say what I'm trying to correct....she jumps up to 200 degrees in no time...plenty of water to therm housing...New circulation pump.....that's the only thing left...I tested the thermostat in a pan on the stove opens up fine.

 

[Alws55]

Well....today I took the front end caps off exhaust manifolds...blew them out and flushed also....no restrictions. I made sure the block was as full as I could get it with a hose thru the thermostat housing. Started it up....disconnected the intake hose at the thermostat housing water shoots out 6" or so and is also coming thru the housing from the otherside.
Reconnected and watched the temp rise to 200....there was water exiting the block but probably nowhere near enough, the exit hoses never got hot just warm, even though the large hose on the recirculating hose was hot.
I then checked the 25 gal barrel the outdrive was in and the water was rust colored....then I shut it down as it creeped over 200 degrees.

Where do I go from here? Pull the heads?
The therm housing top looks good thermostat is set on top of cork washer in recessed cutout and the gasket is on top of thermostat an 1/8" away from moving center. Everything looks to me like the ports in the block and heads are clogged. When I had the circ pump off I ran water into thermostat hole and flushed out the front of block.
To winterize the block I drained water out thru lower end of circ large hose reconnected and poured antifreeze in top at therm housing.

 

[Gilded_Splinters]

I just went through a bit of this myself.

You'll need to temporarily remove the thermostat in order for this to work properly.

I removed the block drains. Not just the caps, but removed the entire fitting from the block.

Then I connected a garden hose to the water intake of the thermostat housing. You'll find that the threaded, male end of your garden hose is a perfect fit into a length of 1" diameter hose. Put a clamp on this and you'll put more water through your block and heads than your raw water pump ever will and at much greater pressure.

I had flow out of the plug holes, but not as strong as I had hoped, so I started poking around in there with a piece of stiff wire. LOADS of stuff came out.

I would pressurize, poke while it was flowing, then let it rest for 15 minutes and drain out so that any debris would accumulate there. Repeating the procedure a few dozen times over the course of an afternoon yielded lots of water flow out of these plug holes and throughout the entire system by the time I was done.

I haven't resorted to this yet, but the next logical step might be to remove freeze plugs and do the same thing. Come to think of it, the ports that your circulating pump attaches to would offer a good shot at blockages in that area of the block as well.

 

[Alws55]

Awesome idea....One drain plug is a welded plug the other I tried but it wouldn't budge and I didn't want to break it off...The freeze plugs are the way to go! Thank you for your insight much appreciated!

 

[Gilded_Splinters]

No problem, glad to help.

You really should try to get those block drains out of there though. They are your only way of really draining the raw water out of there for winterization.

What do you mean by "welded plug"?

In my case, the freeze plugs are a real bear to get at with 2 of them right behind the motor mounts and one on the outward side in a twin engine application. I have only one that I can readily get to.

I had a thread along these lines last week that you might want to check out:

 

[Alws55]

Hey....it looks like a previous owner stuck a piece of steel rod in the hole and welded in closed, they must have damaged the drain ****. when I can get a hold of a torch I'll fix the other. If I drain it as much as I can and fill it with antifreeze isn't that sufficient? I came home today and had the 2 freeze plugs on the front of the block and one on port side rear out in 15 minutes, stuck my finger in there and the grit and rust was 1/2" or more deep. When I put the hose in there it ran black grit and rust for a solid minute. I'll pull the starter tomorrow and finish it. Thanks again I'll post after I finish and let you know how I made out

 

[Gilded_Splinters]

Well, it's great that your freeze plugs are that accessible and that will probably suffice to get the debris out of the block.

" If I drain it as much as I can and fill it with antifreeze isn't that sufficient? "

If by this you mean sufficient for winterizing, I wouldn't feel too comfortable with that. Those drains are located in the absolute lowest point in the water jacket for a reason...to drain out completely. If you leave water anywhere in the block, you will dilute the antifreeze by an amount that you really can't know and open yourself up to disaster.

That said, if you can't use the drains, you can't use the drains. You might have to use a stronger concentration of antifreeze to compensate if you can't confidently drain things out fully.

Lotza Luck!

P.S. Remember to use brass freeze plugs, and not automotive ones which will rust out.

 

[jerryjerry05]

Sounds like the risers might be clogged?
How old?

 

[Gilded_Splinters]

Agreed Jerry...mine certainly were. Earlier, he stated that it was a 1973 Chevy.

He mentioned flushing out the manifolds, but the risers are something to check out for sure.

I didn't have much luck cleaning mine out though. Those passages are narrow and convoluted and were packed with crap.

 

[Alws55]

Hey....will after removing 3 freeze plugs and flushing maybe 2 or more cups of rust and grit out. I filled the block and LG circulation hose with water and ran it for 15 min. Climbed to 180 then up to 200 again. It seems to be seeping out of block thru thermostat. So as soon as I shut it down I popped off the lower end of the LG hose and clear 180 degree water poured out.

 

[Alws55]

If I fill the block thru the t-stat opening and it takes 30 sec or less to fill, doesn't the water just take the same route only in reverse. If it does the ports don't seem clogged at all. Any feedback?