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Mercruiser overheating help please

7

79delta

New member
i have a 1979 mercruiser it st

i have a 1979 mercruiser it started overheating thi year and i cant seem to fix the problem first off i changed the impeller in lower unit with no improvment next i changed the water pump on the engine still no improvment i used a regular automotive waterpump standard rotation maybe this is my prob it needs to be bi directional? i have also replaced the t stat i can take off the hose were the fresh water enters the engine at idle speed i get about a 1/8 to a 1/4 of a gallon of water in 30 seconds shouldnt i get at least a gallon of water in 30 seconds? if so what could i have done wrong during the impeller insallation?

thanks
josh
 
"Welcome Josh:

Was the impe

"Welcome Josh:

Was the impeller you replaced in one piece? If not, there may be a chunk of it in the water tube or it and other debris blocking the oil cooler. You did not say what engine you have. Disconnect the water inlet hose at the back of the engine on the transom and stick it in a bucket. Now disconnect the other end of the hose at the T'stat hsg. Shove a garden hose in it on high pressure to back flush that hose and oil cooler; look for debris in the bucket. You may need to disconnect the cooler to look for obstructions.

Now connect a length of hose to the inlet connector and place it in the bucket. If you have a tub you can fill w/water and lower the OD into you can check the output of the impeller. Disconnect the coil wire, fill the tub with water and have someone crank the engine for 15 - 30 seconds while you watch. You should see a good shot of water coming out the water inlet connection.

If the flow is not strong look at the molded water hose from the OD to the outer transom; it may be kinked, have a flat spot on it or a tear which would impede water flow especially if you store your drive in the upward position. If it is not kinked or torn stick the hose nozzle in the outlet of the OD inside the boat and flush back to the impeller. Drop the LU and see what came out. Check for water in the LU oil by loosening the drain screw. If you get water then the water tube is misaligned or the lower half of the impeller case is leaking. Good luck."
 
"Since yours is an outdrive, t

"Since yours is an outdrive, the rotation is correct--no outdrine motors were reverse rotation.

Keep looking for debris clogging the motor or exhaust risers. If the water can't get out, it also can't get in.

Jeff"
 
Thanks Guy G. I will try that

Thanks Guy G. I will try that this weekend and let you know what i find because the impeller that i took out did have some chunks of the finn missing
Thanks Again
Josh
 
Josh:

You have to find thos

Josh:

You have to find those chunks of impeller; that's your flow problem. Backflushing and flow testing will tell you where the chuncks are located. Good luck.
 
"One pint or one quart of wate

"One pint or one quart of water where the hose connects to the engine is way to slow.
I would not go any further until the flow at the engine connection is more than a gallon at 30 sec.
You will have to drop the lower unit and back flush. Use something to catch the crud in order to determine if flushing is doing any good. Before flushing, pour a bucket of water down the hose where it connects to the engine and determine the amount of flow (guestimate). Back flush the (*&*&^%*%) heck out of it. Check to see if any crud came out then do the bucket thing again to determine if flow improved. You will have to have free flowing volume and if in doubt you may have to pull the outdrive and examine the water port between outdrive and stern assy.
While the lower unit is off, pour water down the top of the water pump and see if it leaks out the bottom of the pump assy or top of shaft seal. If it leaks, it is assembled with gasgets in wrong location. Also, the impeller must be installed with the correct rotation.
Do not back flush the engine with the raw water supply hose connected to the engine because any stuff flushed out will end up in the outdrive pump.
Good luck"
 
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