Merc 40 overheating any help much appreciated

[MystyBlue2]

Hi folks i fitted a new thermosat and poppet today as they where originally missing completely when i purchased the motor.

Fitted them correctly followed my owners manual and started the motor.

Now it is overheating badly!

I removed the tstat and poppet and re installed incase i fitted wrong and same thing.

Then i totally removed the tstat and poppet and ran with them missing as i was suspecting these where causing a "blockage" and same thing. On all occasions i have a very strong telltale so im assuming that the impeller is ok. The telltale warmed up to luke warm but all of a sudden went scalding hot couldnt keep my hand under telltale and was steaming badly, The exhaust manifold and power head was that hot i couldnt touch it.

Im absolutely stumped as to what could cause this. I was putting it down to incorrectly fitting tstat and poppet but its still happening when i totally removed them. Im getting a strong telltale too so im assuming the waterpump is fine.

This was not happening the last time it was started in early December so its something totally new.

Any ideas on what this could be?

Cheers folks

 

[tico]

Blocked waterways in the block

 

[paulajayne]

Blocked or partially blocked intake, Raw water filter blocked?

 

[MystyBlue2]

Blocked waterways in the block

So would removal of GB and backflushing through tstat housing with warm water solve it?

 

[MystyBlue2]

Blocked or partially blocked intake, Raw water filter blocked?

Didnt even know it had a water fliter lol. Cheers il take a look

 

[QBhoy]

Is this happening at idle only ? The poppet valve will only be in effect higher up the rpms when the spring in it has been overcome.

 

[MystyBlue2]

Is this happening at idle only ? The poppet valve will only be in effect higher up the rpms when the spring in it has been overcome.

Yeah i suppose its been idleing on the muffs and cant really give some some with limited water flow on the drive.

This also happened when i totally removed the tstat and poppet.

Does this mean that as long there is an poppet valve fitted it will always overheat at idle until i give it higher RPM and open the poppet up at sea?

Is there any danger in leaving the tstat and poppet removed permanently and running without them at all?

Cheers

 

[QBhoy]

Yeah i suppose its been idleing on the muffs and cant really give some some with limited water flow on the drive.

This also happened when i totally removed the tstat and poppet.

Does this mean that as long there is an poppet valve fitted it will always overheat at idle until i give it higher RPM and open the poppet up at sea?

Is there any danger in leaving the tstat and poppet removed permanently and running without them at all?

Cheers

Ok. Have you had the exhaust section to mid section apart ? Is there cooling water coming out the lower unit or idle relief ports on mid section ?
How hot was the tell tale water ? Like could you hold your hand in it for more than 3/4 seconds ?

 

[MystyBlue2]

Ok. Have you had the exhaust section to mid section apart ? Is there cooling water coming out the lower unit or idle relief ports on mid section ?
How hot was the tell tale water ? Like could you hold your hand in it for more than 3/4 seconds ?

No i couldn't, telltale was scolding so was the head.

Ive had nothing apart and there was droplets of water on exhaust port and there was several holes on gear box and mid section had water coming out aswell.

Telltale was strong and luke warm at first then went red hot so i killed the motor to prevent damage.

 

[BruceK]

Was the OB ever on an boat on a drying mooring? It is possible mud and salt crystals or aluminium salt oxides have created a cement that is blocking the internal cooling passages or waterjacket somewhere (i.e. the motor wasn't regularly flushed with freshwater)

 

[MystyBlue2]

Well i have back flushed ot today with warm water with gear box removed, i also inspected impeller to find 1 and a half blades where missing,

So sitting underneath the leg is now all parts of broken impeller aswell as a small mount of sand and grit and a small leaf!!

I was hoping to leave the water pump rebuild kit until spring but ive had to do it now. Put all parts back together again and now with tstat and poppet installed she now runs like a champ with no overheating and the telltale is like a firemans hose!

Head gets hot but thats expected and telltale stays luke warm

Looks like it was quite a bad blockage and backflushing with foot off sorted it!!

Thanks for all your comments folks much appreciated ?