Cobra 3.0 Overheating-NOT the impeller

[schwahn]

Hello All,<br /><br />I did check past posts and can't find a problem with the same symptoms as this one (FYI: 1988 OMC Cobra 3.0 on a 1988 Four-Winn Freedom 160)!<br /><br />With the muffs on my engine heat quickly went to 200 degrees (engine is tilted up about 20 degrees from horizon) in about 5 minutes. While I did replace the impeller last year I did a quick check to verify that the impeller was OK and that the shaft was rotating (quick turn of the key only). I was puzzled because the water coming out of the engine was NOT WARM (from bottom of stern drive near the transom)!<br /><br />I then proceed to the thermostat thinking it was plugged with previous impeller vanes or rust. When I pulled the thermostat the entire thermostat area WAS BONE DRY (so I'll assume no water was in the water jacket because I drained and pulled the frost plugs before winter)! <br /><br />We (my brother and I) then decided to fill the thermostat are with water in an effort to "prime" the cooling system but this didn't work either. We were not sure which or the larger hoses were the water supply so we decided to stop at that point and ask the experts here at iboats (by the way, you guys are great)<br /><br />So what should I check from here?<br /><br />Thanks guys

 

[schwahn]

Re: Cobra 3.0 Overheating-NOT the impeller

After thinking about this overnight I am going to guess that the passage from the lower unit to the cooling block is blocked or the water pump may not be working. Is there any diagrams that someone could point out as the user manual does not have much detail. Thanks-Brian

 

[bigdaddyofhouse]

Re: Cobra 3.0 Overheating-NOT the impeller

Back wash the hose leading to the stern. But first remove your impellor.

 

[schwahn]

Re: Cobra 3.0 Overheating-NOT the impeller

Thanks for the response but that is where we are lost (hence my request for diagrams because I cannot tell which one leads back to the stern). I have the ownwer's manual but it does not indicate which two larger water hoses (port or starboard side) that are connected to the water pump is the "intake" side (which is suggested that I back flush). It appears that the small hose connected from the water pump is the "exit" side for the cooling system (this is a question, could somebody confirm this as I am trying to determine if I have another problem brewing)?<br /><br />Thanks again!

 

[sea wolf]

Re: Cobra 3.0 Overheating-NOT the impeller

It's neither one of the large hoses. It's the small hose on the starboard side that connects to the t-stat housing. Pull the hose & start the engine with muffs on. See if water comes from the hose. If not, your problem is in the water pump. I will put money on a bad impeller. Did u check it again after it overheated? Remove the triangular cover. Turn on the hose & see if water squirts from the vent hole on the pump cover. If not, then either u don't have enough water pressure, the intakes are clogged or something is amiss in the lower unit which is unlikely.

 

[schwahn]

Re: Cobra 3.0 Overheating-NOT the impeller

UPDATE:<br /><br />Well, we were about to flush the hose when my brother spotted the problem...the hose had fell off the lower unit!<br /><br />After about an hour and a half (very tight fit, we had to do a lot of movement of the trim on the motor) at about 90 degrees with about 100% humidity we got the clamp on and everything seems OK. <br /><br />Thanks everyone for their help!