Overheating outboard and really stumped help

[Garnboatingfamily]

Hi everyone, we have a evinrude vro 40hp 2stroke engine that starts and runs on the button but when we went out it had no power and overheated within 10mins of leaving the launch ramp. Engine has a strong stream, we've changed the gaskets thermosat, impellor given it a quick clean out but we haven't tried it on the water again because the engine after running 5 10 mins on the hose is burning hot and water stream cold then very luke warm back cold ect but the motor is too hot to touch and cut out, in a bucket it runs lumpy sounds like it's suffocating. We are stumped any ideas??

 

[spannerman]

Try running it with the thermostat cover off to see if the block fills up with water. I suspect it doesn’t which points to low pump pressure not being able to push enough water up to the top of the ebgine.

 

[MystyBlue2]

I had same problem with mine back in may, along with a stuck thermostat it turned out to be a blockage in one of the jackets somewhere i could not reach, all i did was fill up a test tank with warm water NOT hot and add to correct ratio of automotive rad flush as its safe for gaskets, seals and aluminium, ran it at idle in 10 minute intervals ( without thermostat ). Did that about 5 times to allow water in the tank to cool and so there was not too much heat being built up with no thermo. Then i put a hose pipe to the thermo housing and backflushed for 5 mins. Then reinstalled a new thermo.

Solved the problem for me

Also take off the lower leg if your going to back flush, if no water comes out then there may be a blockage in the main leg. Impeller might be working strong but a blockage higher up in the leg or head jackets can be a right ball ache but easy fix.

Hope this helps

 

[Garnboatingfamily]

I had same problem with mine back in may, along with a stuck thermostat it turned out to be a blockage in one of the jackets somewhere i could not reach, all i did was fill up a test tank with warm water NOT hot and add to correct ratio of automotive rad flush as its safe for gaskets, seals and aluminium, ran it at idle in 10 minute intervals ( without thermostat ). Did that about 5 times to allow water in the tank to cool and so there was not too much heat being built up with no thermo. Then i put a hose pipe to the thermo housing and backflushed for 5 mins. Then reinstalled a new thermo.

Solved the problem for me

Also take off the lower leg if your going to back flush, if no water comes out then there may be a blockage in the main leg. Impeller might be working strong but a blockage higher up in the leg or head jackets can be a right ball ache but easy fix.

Hope this helps

So even with a strong stream it could still be blocked ill be tool ready tommorow morning to give this a go.. Thankyou

 

[Garnboatingfamily]

Try running it with the thermostat cover off to see if the block fills up with water. I suspect it doesn’t which points to low pump pressure not being able to push enough water up to the top of the ebgine.

I'll give this a go new to boating so learning as we go when we took the jacket off it was wet inside the deepest part but dry as a bone on the outer channels but we'd left overnight so assumed it had dried up. So I'll be giving these recommendations a go. Thankyou

 

[lynallbel]

Pls correct me if I am wrong, but an out board with a stat will be at operating temp when used, then stopped, and some time later run up on fresh water ie the engien will have cooled and the stat will have closed, so the short flush time is not long enough for the stat to open? so the waterways will be clear apart from in the powerhead itself which over time will salt/crud up?

 

[MystyBlue2]

Pls correct me if I am wrong, but an out board with a stat will be at operating temp when used, then stopped, and some time later run up on fresh water ie the engien will have cooled and the stat will have closed, so the short flush time is not long enough for the stat to open? so the waterways will be clear apart from in the powerhead itself which over time will salt/crud up?

Yeah thats why i backflushed with stat out to allow all internal jackets to receive water otherwise i would have to wait untill it was hot enough to open stat or (overheat in my case). Defo worth a shot backflushing seemed to help alot.

 

[MystyBlue2]

So even with a strong stream it could still be blocked ill be tool ready tommorow morning to give this a go.. Thankyou

Yeah the water pump might be strong enough to pump water up the main leg and out the telltale but a blockage in any of the jackets in the head will cause it to overheat, bearing in mind these are tiny passages and built up salt crystals or currosion of the aluminium or tiny bits of broken off impeller from the past might have worked its way up to these jackets and causes alot of problems. If you can remove the stat have a look down as far as you can, if the housing itself is badly corroded then you can guarantee that the small passages deeper in are the same condition, run in a tank with rad flush will gently disolve any salt and crud and a backflush with a hosepipe will hopefully dislodge any old bits of impeller, repeat this a few times with warm water. Hope this helps

 

[Garnboatingfamily]

OK so flushed top half and run without thermosat and run lovely also the water outlet on the leg was dribbling something I'd never noticed before. So gave it a quick flush again and put thermosat back in and it overheated again. Tested the new thermosat definitely working also no water coming out of water outlet on leg when thermosat in. We left it run long enough to get hot thinking thermosat won't kick in until hot allowing flow to the top but nothing arrised a slight dribble that was momentary out of the leg but tell tale is like a jet wash coming out. What you think leg off? Flush it out from bottom up or bottom down?

 

[MystyBlue2]

OK so flushed top half and run without thermosat and run lovely also the water outlet on the leg was dribbling something I'd never noticed before. So gave it a quick flush again and put thermosat back in and it overheated again. Tested the new thermosat definitely working also no water coming out of water outlet on leg when thermosat in. We left it run long enough to get hot thinking thermosat won't kick in until hot allowing flow to the top but nothing arrised a slight dribble that was momentary out of the leg but tell tale is like a jet wash coming out. What you think leg off? Flush it out from bottom up or bottom down?

I would personally remove the lower unit and try backflush in stat housing with warm water and keep an eye on water coming out of the water pump pick up tube, if all fails maybe a wire coat hanger straightened gently prod up the pick up tube to dislodge any blockage, or put on hose pipe at the lower part of pick up pipe and try flush up overs, bear in mind this could push any blockage higher up so be very careful

 

[MystyBlue2]

How far did you get with this? Any luck with the fix?