Heating problem

[CarbonKen]

Over Heating Problem 350 Chevy no style / inboard direct drive ( New complete rebuild ) . Used log manifolds end riser style( they were new one year ago . Pressure checked OK . Thermostat housing Mercrusier style 160 Deg. marine thermostat . 1.25 " intake raw water crank mounted pump New 1.25" X 1.25" Sherwood stainless . Circ pump short nose ( Old style ) Engine over heats after short periods of use !??. I removed check balls from tee to manifolds , even the thermostat / NO CHANGE !. Pressure checked cylinders for head gasket leaks NONE !. Raw water comes in goes to Therm housing divided chambers off to the circ pump and maifolds . What am I over looking ?. Thanks for any suggestions . If I can help in any composite construction or repair questions just ask me . CarbonKen

[Thunderhead19]

Engines running lean will run hot. Air pockets in cooling system? Is the cooling system ingesting air when you're runnning?

[CarbonKen]

It's more like the water is not circulating through the block !. It has me baffeled to no end . Block was hot tanked solvent cleaned then rinsed very well , for urethane paint !. This is an old style intake manifold with NO pipe plug in the cross over tube . I don't understand how air ? could be getting into the system . Raw water pump picks up through intake strainer then into the thermostat housing ( Mercrusier style ) then into the water circ pump . Standard rotation clock wise 350 small block chevy . Then excess water is fed into the " Tee ", 1 " hoses go into the 1/2" pipe thread in the end of the manifolds through the log back out the same end up through elbows and hoses too the collectors which spray the water into the exhaust flow and out through transom dumps . Where does air get in ?. I thought maybe circ pump was wrong direction . Wrong ! ,they are bi directional for chevy !. I don't know how that works in it's self !!!!!???. Every pump I have delt with has an in and out , for cavity and impeller spin !. So how or why are chevy water pumps bi directional for marine use . Automobile are not !!!!!!!!!. I even removed the thermostat just to see if it made any difference it did NOT !!!!!!!. This is a standard V belt tensioned properly !... CarbonKen ????

[tone it down]

just my 2 cents if your getting water coming out the exhaust is it a trickle or flowing properly ? since it is a new motor did you degree the cam in ?
and set the timing ? along with setting the fuel rich or lean what style carb are you running ?

[CarbonKen]

Everything works just fine except it over heats after the motor warms up !. I removed the thermostat made no difference !. I put a water based dye in the block water ( Removed therm housing filled block added dye , replaced with thermostat ) It flows very well when it comes up to temprature 160 degrees , thermostat opens at that temp . I checked it to in a pan of heated water . .Green dye came out with the rest of the water flow . Water exiting the exhaust full flow all the time by design of Merc. thermostat housing by passes to the maifolds . I now am wondering if the exhaust log style manifolds with their 1/2" pipe thread are to small ?. Therm housing has 1" Tee for flow , I had to neck down to 1/2" so as to accommodate them !??. I can't figure anything else that could be wrong . I have triple checked EVERY thing else . Even if the motor were running lean it should still cool at an idle . I see no signs of excess heat damage to plugs !??. Exhaust is cool to the touch no matter how hot block water becomes , because of the raw water going through the tee then to them .. It has me really stumped and I'm not one to be stumped easily !!!!!!!!!!!...

[Roy Sparks]

I have a similar problem with my Bayliner, but mine was not new, just started getting hot under running power and cools down when idling down. Have replaced the lower unit water impeller (didn’t look bad) and this took care of the problem for about three weeks and the problem came back. Changed the thermostat twice. I checked for any restriction through the block (removed all hoses and ran a water hose through all openings) and everything flowed great. Removed the circulating water pump and it too looked and felt fine. Ran the water hose through the opening in the block (where the water pump was removed) and it filled up the block and ran out the thermostat opening at the intake manifold. Does anyone have any other ideas or experiences.

[san]

CarbonKen

I aint an expert, see my thread "Cooling problem Ford 302" where you have been giving me your thougths (thank you), but can you be sure you dont have a cracked head for example if you just check for leaks with airpressure? Crack may only give effect when engine is warm. It sure sounds like you have exhausts stopping up the circulation.

I haven't got my engine to run yet, but I put transparent hooses between engine and exhaust manifolds to see if there were any exhausts in the cooling system. This worked fine as a test.

San

[Frosty]

How do you know its getting hot?, because the guage says so? Check the guage by removing the sender unit and place it in a kettle, or water heater of some kind with a thermometer in it. Wire connected of course. You will need to ground the outside of the temperature transmittor to the block .No need to start the engine just turn on the ignition and check the guage against the thermometer.

[Roy Sparks]

Good idea, I have questioned the gauge and am going to use a ifnra-red heat sensing gun that I have access to, to read the temperatue of the block when the gauge shows hot. After this I may still to the boiling test. Thanks for the info and I'll let you know what I find probably next week.