Overheating motor

[alldodge]

With large amounts of air, I'm thinking a blown head gasket. I would do compression test first because its easy. If compression checks out even on all cylinders and no wet plugs, then look at the drive pump housing and impeller

 

[Chapparall280]

yes I will do compression check.

Just to clairify If I am seeing air when pulling the hose from thermostat that is fed from the drive I was thinking it would not have made its way to the engine so the air would not be from a potentially blown head gasket since the air came before the line made it to the engine. Is the correct or am I missing something. Thanks again for all the assistance

 

[alldodge]

For a small/medium amounts of air yes, water pump and hoses

For large amounts of air, cylinder gases blows back toward the thermostat housing and can almost stop all water going to the motor

 

[Chapparall280]

first thanks again. So update. Compression is as follows
plugs order 1-4 from front port to back and 5-8 starboard front to back

So that appears good

1. 170
2. 160
3. 170
4. 155
5. 170
6. 150
7. 175
8. 175

 

[Chapparall280]

Video attached regarding water flow. One idle. Looks what appears normal. One 1500 rpm. Also somewhat normal. One 2000 rpm basically have water flow stopping. These are all while at the dock not moving.

 

[Ralph V]

First let thank anyone for the help.
I have a 2002 Chaparrall 280 with a mercruiser 5.0 and alpha one gen 2 drives. It's a carb motor and has approx 600 hours.


I have what appears to be an overheating issue. The alarm sounds and my temp gauge acts a bit odd during this time. Goes from 160 which it stays at steady as long as I keep it below 2000 rpm. Ten seconds after I get up on plane the temp goes up to 180 then will oddly drop to 120 then stay there or come back up to 200. I shut the motor down or pull back to neutral and the buzzer will go off and temp will go back to normal I can run day at 2000 rpm just putting along.

I have read many threads on different overheating and corrected several possibilities

I have replaced
impeller and housing,
replaced risers , manifolds , Elbows.
-replaced the Thermastadt, sensor and sendor and ran without thermostat
-tested water flow to thermastadt at idle hood water flow
heat temp gun and although this motor gets 15 degrees warmer then my port motor it has the alarm sounding when the thermostats housing is 180
move also checked power steering cooler line and the exhaust bellows appear clear

I will test head gasket but no reason to think they are bad

was goong to look for air in the line by connecting a clear hose To intake line but assuming I do see bubbles at higher rpm's. Where else could air be coming from. Again not sure if their is air in the line but what else could
it be. Saw someone suggested the hose that comes from drive thru transom could collapse at higher RpMs. although others say unlikely as the water pressure is expanding the hose.

I appreciate any direction as can't use the boat like this and all mechanics are 3 weeks out and in the north east short summers. Thanks

:
I am def getting air in the line. Without even taking the boat out I could see air in the line when rpm taken to approx 2000 or little over. When backed down to idle still had mostly air but when bumped to 1500 rpm had consistent water flow. When went up again large amounts of air not just bubbles but air sitting there. So my question is where all can I look that it could be sucking air in ?? I had thought since drives are under water and not on plane does that eliminate the chance of the air coming from the lower unit as I would think all areas would be filled with water. ( I may be wrong with that of course.). Just trying to determine where to look. Thanks again

I had the same issue overheating on plane. I have a 2004 signature 330 with volvo outdrives and the issue was a cracked hose barb nipple sucking air in the fresh water intake in the outdrive. Hope this helps

 

[alldodge]

Compression numbers are good.
Vids show the pump is not able to pump move water. Remove drive and check the connections and hose fittings. If they all look good, then need to get back in the drive

 

[Chapparall280]

Ok thanks on both suggestions will check again