Overheats idling on lake-nice and cool (140 degrees) on muffs and cruisng on lake

[jimrockireland]

I have a 1983 Wellcraft 196 Sunhatch with a MCM228R engine and "R" sterndrive. Replaced impellor but engine runs hot when idling (> 180 degrees) or at low cruise RPM's on lake. It runs about 140 degrees when I have it out of the water on muffs with garden hose going full blast and/or cruising about 2000 rpm's on lake.Any ideas?

 

[Scott Danforth]

did you just replace the impeller or the whole water pump assembly?

were any pieces missing from your old impeller, and did you go thru the cooling system to rind them?

on the muffs, the hose is probably forcing water in there.

 

[jimrockireland]

I just replaced impellor - not the whole assembly. The impellor that was in there seemed to be still good, but I swapped it out anyway. I was wondering if my problem was the sterndrive or the engine. If I get a chance tomorrow I will disconnect the in-coming water hose to the engine and measure the amount of water coming out of the water hose under 2 conditions: 1) With muffs on and 2) with the sterndrive submersed in a big stock water tank. I'm assuming I should get about 4 gallons/15 sec if the sterndrive is operating properly. If I get 4gallons/15sec under condition 1 but not under condition 2 the sterndrive must be faulty. If I get 4 gallons/15 sec under both conditions the engine must have a blockage. Whatever I measure the gallons/15 sec that get circulated in condition 1 should be what is required to have a cool running engine. I'll post back when I get rsults

 

[Scott Danforth]

new to you boat or have you had it for a long time. if this is a new to you boat, the prior owner probably changed the impeller after it broke apart and never looked for the pieces. or the water pump housing melted a bit and is leaking like crazy

raw water output is to be tested with boat in the water (not a tank) and not on the muffs. you need to test the pump with the right amount of feed head (in the water) and not artificially supplied by muffs)

 

[Bt Doctur]

with the sterndrive submersed in a big stock water tank

You cant get the water 5 inches above the cavitation plate

 

[jimrockireland]

Thanks for all the input. I bought the boat about 4 years ago and replaced the impellor right off. The impellor I swapped out looked to be in good shape. For 3 years I have been working on the boat and finally got it in the water this year. The major change was replacing my MCM228R engine block with one from an 898 engine. So what I have is a 898 block with everything else from my old MCM228R.So you are right in noting I don't have any knowledge on the history of the 898 block even though I used the exhaust manifolds and risers from my MCM228R I understand what you are saying about running the boat on muffs and immersing the sterndrive in a stock tank. When I put the sterndrive in the stock tank the AV plate is about 2" under water so you are correct about the water head above the intake vents on the sterndrive being less than when they are on the lake. My thinking was when I put the muffs on, the engine runs nice and cool so whatever water flow rate I measure is adequate to keep the engine cool. If I I run the sterndrive in the stock tank and get the same flow rate as on the muffs I know I have an engine problem. If The flow rate in the tank is a lot less than what I measure on the muffs I won't know if the difference is due to the lower water head or something else. I think by noting the engine temperature when I run in the stock tank I can get a sense of engine temperature vs. water flow.

 

[Scott Danforth]

Put boat in water, not just the outdrive.

 

[jimrockireland]

Experiment was a total disaster , but uncovered a bunch of other fixes I need to do over the winter. I didn't have the option of putting the boat in the water since I need another person to help load/unload the boat and my kids are only around on weekends. Under both conditions (muffs on/sterndrive in stock tank) I couldn't get any water to come out of the water hose going into engine. With the water hose re-connected and under same conditions I also couldn't get any water to exit the sterndrive. I'm guessing somewhere along the line my sterndrive water pump failed. I'll have to disassemble the sterndrive to take a look. I also found sterndrive oil leaking out of my u-joint bellows and onto the exhaust bellows (only when sterndrive raised up). It looks like I have an oil leak out of the U-joint and a hole in my U-joint bellows. I am going to have a busy November