help wierd overheat

[sparky192]

ok here it is
1974 silverline antigua 18t running ford 302 mercruiser 888 ( 188 hp 351W heads)
On the hose and earmuffs it seems fine.
put it in the water it seems to build pressure in the block and forces hot water down the cold water line toward the impeller. Engine overheats and blows steam.....
Have replaced the impeller and cold water line and all boots. Replaced head gaskets and manifold gaskets....Checked timing, had valves done and head planed and magnafluxed.......I suggested cracked block to my guy at the engine rebuild shop, he says no, cannot be without water in a cylinder or in the oil which there is not:facepalm:
so what is happening????????????

 

[Don S]

Re: help wierd overheat

It could be a cracked head or block. To find out, you need to do a leakdown test on all cylinders. Trick is to block off all water hoses going to the manifolds. Then remove the hoses going to the elbows and tie them opening facing up and fill the engine with water. Now, when you pressurize the cylinder as in the leakdown test, if you see bubbles, you have a combustion leak into the cooling system, and you will know which cylinder it comes from.

 

[Bondo]

Re: help wierd overheat

Ayuh,... Are ya gettin' Good water flow, comin' Outa the motor,..??

 

[sparky192]

Re: help wierd overheat

Ayuh,... Are ya gettin' Good water flow, comin' Outa the motor,..??

Yes the water flow is good at first, for maybe 8 or 10 seconds then it stops and the cooling intake line gets hot

 

[sparky192]

Re: help wierd overheat

It could be a cracked head or block. To find out, you need to do a leakdown test on all cylinders. Trick is to block off all water hoses going to the manifolds. Then remove the hoses going to the elbows and tie them opening facing up and fill the engine with water. Now, when you pressurize the cylinder as in the leakdown test, if you see bubbles, you have a combustion leak into the cooling system, and you will know which cylinder it comes from.

Hi don,
Yup I totally agree - the way I see it the combustion pressure when it fires may force air (gases) into the cooling system that may not pass water into the cylinder.... My engine man has been in the business for a lot of years and he says a leak down test is a waste of time. But, I dont want to tear this mill down with no idea what I am looking for. It could be a hundred thhings.... I guess I need to build me a leak down tester - used to use them a lot on aircraft engines - better than a simple compression test - which BTW on this engine reads 85-90 PSI across the board.
Thanks

 

[Don S]

Re: help wierd overheat

You don't even need the full leakdown test, just pressurize the cylinder while on TDC of the compression stroke on each cylinder and look for bubbles.

 

[Bondo]

Re: help wierd overheat

which BTW on this engine reads 85-90 PSI across the board.

Ayuh,... That's 10 to 15psi, Past worn out....

 

[sparky192]

Re: help wierd overheat

Ayuh,... That's 10 to 15psi, Past worn out....

okay but look at it this way, the engine was seized, I broke it loose, there is light rust in the cylinders, and no ridge at all in the cylinders, I am hoping the compression will climb as it reseats rings and polishes cylinders, besides I want to know if the block is cracked or if it is something else before I spend any more money on it. I am going to find or build a pressure leak down tester and try that next...... thanks

 

[c384id70]

Re: help wierd overheat

ok here it is
1974 silverline antigua 18t running ford 302 mercruiser 888 ( 188 hp 351W heads)
On the hose and earmuffs it seems fine.
put it in the water it seems to build pressure in the block and forces hot water down the cold water line toward the impeller. Engine overheats and blows steam.....
Have replaced the impeller and cold water line and all boots. Replaced head gaskets and manifold gaskets....Checked timing, had valves done and head planed and magnafluxed.......I suggested cracked block to my guy at the engine rebuild shop, he says no, cannot be without water in a cylinder or in the oil which there is not:facepalm:
so what is happening????????????

I had this problem and finally after a very long time and lots of money found out it was the V8's circulation pump. The vanes on the old pump were so worn out that there was over 1/8" gap between the impeller and pump base. AL the water was bypassing its intended route because of this wear. The new pump I purchased had a bronze impeller and the old one was cast iron, so the new one won't rust away. Also, the former owner ran it through a lot of shallow water and hence sand was also cutting away at the impeller and pump body. Now the boat runs in Lake Michigan so shallow water shouldn't be a problem for me.

 

[achris]

Re: help wierd overheat

You are replying to a year old thread....

Chris......