I am a new member, and a long time Corvette owner, but my current problem is with a generic 350 engine.


I have a boat with two Crusader 5.7 engines, which are really 2002 crate engines set up for marine duty. I have an overheat on one that only affects the left cylinder bank. I recently bought the boat used, so the problem predates my ownership. The water pump, the 160 thermostat and the 7 pound pressure cap were replaced just before I purchased the boat and the mechanic thought that fixed the problem (but did not). I accepted the bad information as factual and shipped the boat to Mexico where I fish it. Once there, I found that anything other than idle it will exit boiling coolant from that side of the engine to the intake manifold after 10-20 minutes of operation. The IR gun says all other temps in the engine are correct. Tests for exhaust gas in the coolant or immediate pressure rise on startup in the coolant are negative. All cylinders test over 170 psi compression with little variation and no leak down. Pressurizing each cylinder with 140 psi air does not cause a pressure rise in the coolant. So, it does not appear the overheat is caused by a combustion gas leak. Still, I pulled the head anyway and could see signs of overheating on the gasket between #3 and #5. New gasket installed, and the overheating is still there. I am now focusing on coolant flow. I found that if I remove the thermostat, the increased flow is enough to cure or mask the overheat, but the engine runs very cold (115-120....lots of carbon) and a pressure gage on the coolant shows a lot of bouncing around at higher rpm (I presume pump cavitation issues). So that is not a long term solution.


The next step is to take off the new water pump and examine, and then remove the left head (again) and really look hard at water passageways for flow restrictions (which I should have done the first time). BUT, has anyone ever experienced a water pump that preferentially fed fluid to the right side of the block instead of equally to both? As you know, there is one entrance and two, supposedly equal, outputs. For example, could flow restrictions going into the pump cause such an unequal outcome? Or anything else you can think of? Because if I do not find a blockage then what else could reduce the coolant flow on that side?


Thanks for any ideas.

 

Did you check for cracks bettween 3 and 5 cylinder? If you have the head offf, I'd check that even with dye penetrant.

 

Are these engines both the same rotation? If not maybe the wrong water pump is installed. Or maybe used the old w/p and it is the wrong rotation.

 

Both engines are normal rotatation. The shaft direction is reversed on one in the transmission.

But, in reviewing old test information, I now realize I have good reason to believe the system is not holding pressure. Since I have a new cap I think the leak is in the fill riser (on this boat is sits separate and is only connected to the engine by a couple of hoses) so I have ordered a replacement. The engine acts as if the lower cap seal (that holds the pressure) is leaking but the upper cap seal (that directs the overflow to the overflow tank) is OK. I am not sure as to why this would cause a localized overheat in the left bank, but suspect it is either a collapsing feed hose to the water pump (because of no internal pressure) that reduces flow to the system, or because the lack of pressure allows air to enter the system once the expanded fluid exits and the air collects on that side. In either case it means the system is not perfectly balanced (side to side) but that may be true of all engines. And of course the absence of the 7 psi means the boiling point is lower. So I need to find and fix the leak and then we shall see where we are at.

Thanks for the responses.

CaboJohn

 

I'm thinking it's Casting Sand trapped in there. Unfortunately by now, just shaking the Block isn't going to knock it loose.

I'd pull the Head, Pump and "if" there are any Freeze Plugs, remove them too, get a flexible cable and start prodding every orifice in every direction you can, as you flowed water through that area with a hose.

You might even get a Water Hose to 1/4" Copper Tube Adapter, with about 12-14" of Copper Tubing, and put a short 90° bend in the end, run it down into the Block, and direct the flow sideways down through the water chambers. Be nice if you could get that Adapter on the end of a High Pressure Pump (originally 1500 psi or so).

 

maybe the problem isnt holding the pressure, maybe its the building of pressure that is the problem, and also my 350 used to run hot till it popped a head gasket when i took it apart i realized the coolant holes to the head are restricted huge by an un modified gasket, so i cut them to a larger size, now its fine

 

If you think you have a pressure loss, you can get a hand pump that replaces the radiator cap. Pump it up to 15 lbs or so, and watch if it drops. If you have an external leak, you can find it. Internal leak, check the oil didpstick, also in the tranny fluid, oh wait this is on a boat?