75hp pumps water only at Idle,not at speed

[JDA45]

Chrysler 75hp. Just rebuilt motor and replaced impeller and gasket. Took it the the lake first time today.Noticed no water coming out telltale or pee hole. Stopped boat and at Idle water was spitting out along with steam.Took home tore down <br />water pump, looked ok. I plan to blow out water line and other water compartments with air compressor. Hook garden hose to water line from water pump and see if water circulates. Reinstall impeller with sealer on gasket and screws.<br />What else can I try?

 

[eurolarva]

Re: 75hp pumps water only at Idle,not at speed

Is the impeller key or pin in. Not sure if yours has a pin or key. IF pin is in look at the middle of the impeller. Does it have a metal hex nut in the middle. Maybe a long shot but mine looked good but found that the adhesive the glues the metal nut to the rubber had become detached. the center of the impeller would spin but the outer part would not.

 

[scotiany]

Re: 75hp pumps water only at Idle,not at speed

It almost sounds like a stuck thermostat

 

[JDA45]

Re: 75hp pumps water only at Idle,not at speed

Thanks guys for the replies.<br />My impeller has a half moon key in it.<br />The impeller looks good.<br />My engine has no thermostat.<br />Before putting lower unit on I ran the motor using a garden hose on the water inlet tube.<br />No blockages. I believe it's in the pump some where. The stainless steel back plate under the impeller was a little warped and had some groves wore in it . Thanks again, and keep the suggestions coming.

 

[scotiany]

Re: 75hp pumps water only at Idle,not at speed

Actually, you don't need a thermostat if the lake your in has a constant temperature of 143-145 deg.

 

[The Marine Doctor]

Re: 75hp pumps water only at Idle,not at speed

JDA45...you say you just rebuilt the motor. I assume you used RV silicone in place of 1 of the base gaskets..as the manual should have told you too. <--as this gasket is NLA.<br /><br />The water intake for the block sometimes gets blocked when excessive RV silicone is used. I would think this might be your problem.<br /><br />Also make sure you did not blow the head gasket, and are pressurizing the water chamber.<br /><br />TMD

 

[JDA45]

Re: 75hp pumps water only at Idle,not at speed

UPDATE<br />I removed the lower gearcase and hooked garden hose to water tube. Some water came out of telltale but most of it came out of two holes beside where water tube mounts to plate.These look like bolt holes.<br />Could be where the water tube bracket bolts on.<br />I tried hooking garden hose up to telltale and again most of the water came out of the two holes not the water tube. When rebuilding motor I didn't take the water tube lose. But I did have to make my own gasket. The gasket between top of motor leg and the spacer plate. That gasket was not in the kit I bought. Looks like I will be pulling off powerhead to get a look in there.<br />Thanks for suggestions. Any more Idea's welcome.

 

[eurolarva]

Re: 75hp pumps water only at Idle,not at speed

You mentioned you tried running water through lower unit without it connected to motor. Your water will not pass because you need the motor to run so the impeller spins in order to get the water to flow up the tube. A better test might be to remove the impeller, replace the water pump without impeller and try your test again. YOu should now get water running out the tube. Another thing then is to hook water tube to motor and run water up the tube with a garden hose. Without a thermostat you should get water out the telltale. <br /><br />YOu really should put a thermostat on that motor. Without thermostat your motor takes much longer to reach operating temp. Spark plugs run cold, Fuel will not atomize properly, and plugs are more prone to foul.