omc overheating

jimd10

Recruit
Joined
Nov 19, 2014
Messages
5
Hi guys
I have a 5.7 omc1987 and cobra outdrive,raw water cooled.I have no water at the inlet hose on the thermostat housing.I took off this pipe at the housing and ran water through it with a garden hose. It came through at the impellor housing ,left hand port as you look at it,so no blockage at the oil cooler.The impeller is in good condition,no splits ,cracks or any signs of damage. The boat is on the hard with the drive in a tank of water.The inlets are under water and were clear before I filled the tank.
What am I looking at here?
Thanks for any replies in advance
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,307
welcome aboard

use a set of muffs, unless you get the boat floating in a tank to get the water lever up where the pump can draw water, you are starving your drive and motor of water. using a tub or bucket only works if you get the water level up high enough to get the pump to prime. that's why people use a garden hose and a set of muffs, to force the water a bit up the tube to get to the raw water pump. also do not run higher than 1500 RPM on the muffs, you can not flow enough water thru the garden hose
 

jimd10

Recruit
Joined
Nov 19, 2014
Messages
5
Thanks for that Scott,thought for a while I was going to have to split the drive to start looking for blockages.
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,924
Duct tape the muffs in place sealing any spots that can let water out.
The drive needs to be dry when you apply the tape.
 

HorizonblueDK

Petty Officer 1st Class
Joined
May 27, 2010
Messages
355
Inside the outdrive (in the exhaust channel) there is a cupper pipe, going from the lowerunit to the pumphousing in the upperunit. I have seen a corrosion hole in this, resulting in air/exhaust gas being sucked in and the pump failing to pump. How about sealing the intake with duct tape and filling the outdrive with water, from the hose on the thermostat housing inside the engine compartment ? (impeller removed but pump housing installed and the vent hose blocked) No water should come out then.
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,802
No Title

Scott is right, you will never get a Cobra pump to prime like that. The water level has to be over the impeller housing, so the whole drive has to be submerged.
To check the water intake area/water transfer tube/seals, you can do the following:
Remove the impeller housing (sounds like you already did)
Put the muffs on the lower unit. Hold them on tight. Have someone turn on the water. Water should spurt out of the right hand opening in the impeller mount in the upper gear housing. If that works, then you don't have a blockage. The definitive test, is to put a length of clear hose in the raw water intake hose where it attaches to the thermo housing. Run the engine at speed on plane, and see if there are bubbles in that line meaning that it is sucking air. This can happen if there is a small pin hole in the tube, or the gaskets don't seal right. If you can get the upper and lower gear housings apart, its not a bad job to fix. But they can get stuck together. This is how I got them apart (salt water use) all the bolts came out, it was salt deposits round the o ring that held it fast. I put a piece of all thread through the trim ram rod hole. Then 2 half inch bolts and nuts in the lower drive mounting holds. Put a scissor jack under each side of the all thread and one under both of those bolts. Jack evenly and it comes right off.
 

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