Over Heating Problems

All summer long, had a poor to no tell-tail stream, but alarm on my 40 hp 4 sroke yamaha never went off! Today it did, after getting home I pulled the thermostat and found pices of rubber behind it. I started the engine without the cover on the therostat and got water that far. Put cover back on without therostat and got no tell-tail. My questions and comments<br />1. The rubber behind the thermosat was part of the impeller, do you agree?<br />2. What does getting water to the the thermostat mean, can the impeller still be bad? How about the Water pump?<br />3. What other comments, please help

Re: Over Heating Problems

hello<br /> most likly a piece of impeller.<br /> but no worries you have run it this long with no water pressure. keep doing it and you may have an insurance claim. I really cant assist you much cause you told me you noticed a problem yet waited until it failed completly. makes it hard to help. but yes I would pull the impeller or disconnect the buzzer<br /> good luck and keep posting

Re: Over Heating Problems

You can't hit Rodbolt with a story like this at the end of the day, he gets grumpy . You have thrown the arms of the impeller off and they have lodged in your thermostat and Lord knows where else. Its a tribute to the Yamaha impeller that it is still pumping SOME water. There is a lesson to be learned here grasshopper. Pay attention when the motor speaks to you, don't wait for it to yell at you. Run don't walk to the bottom of this web page and buy a manual for your motor. As penance for your sins you should probably buy 2 and give one to the next boater who has a similar story Pull off the lower unit, replace the water pump, check and/or replace the thermostat, and backflush the powerhead from the thermostat housing with a garden hose. Put a bucket underneath the lower unit and count the number of impeller arms that flush out and compare to the number missing. Hope the number is the same.

Re: Over Heating Problems

Thanks for the quick reply! I'm not sure of what you are telling me. The motor was cut off as soon as the alarm sounded and has no signs of being over heated. I didn't mention this in the first post, but the motor is a 2003 Jet Drive. Other then back flushing the head is there anything else I can do? <br />I can't seem to find a manual listed for anything this new nor a Jet Drive. Any suggestions?<br />By the tones of your posts, do you think I've done some major damage? If so what should I be looking for?

Re: Over Heating Problems

Oh. Thought it was an outboard. (Thats why you have to state the make, year, and model). I don't know the water pump setup on a jetdrive. If its the same as an outboard the advice would be similar if its different, nevermind. You may be fine once the cooling system is straitened out, it depends on how hot it got for how long. I think Rodbolts and my comments were directed at the fact that you apparently ignored a poor pee stream for some time and waited for the engine to overheat before you acted. That kinda like watching a mole on your arm get bigger

Re: Over Heating Problems

OK Thanks for your help. This Jet drive engine is the same as any other outboard except that the lower unit is differant. All your advice was useful. I take note about not heading the warning signs, but I always know and checked the engine and it never felt overly hot to the touch. It still starts and was running great when the alarm went off and the second the alarm sounded the motor was turned off. I truely thing that I didn't harm anything, I feel very lucky!!

Re: Over Heating Problems

Oaksmith -- I two own an outboard jet (150 Yamaha). Still have cooling problems - we can compare notes.

Re: Over Heating Problems

hello<br /> the pump assy is almost identical and in some cases is identical to an outboard. some jets have a slightly different housing so when looking at the new ones make sure you ID it as a jet. sometimes the J part of the seriel # is not there.most impeller failures on the jets are due to dry running. others are from slow speed shallow water operation. something a jet is NOT designed for. there is no way to modify the water intakes due to the fact that when on a plane only the intake grate is submerged. yes sometimes after dealing with customers that are bitter cause their machines are broke cause of lack of maint and customer neglect I am a tad grumpy when ya tellme it was dying for months but I ran it till it failed anyway. sorry about that. if the alarm sounded ya overheated it. end of story.<br />the impellers in a jet also like to cavitation burn due to air in the intake water. so I reccomend pumps in jets to be changed at least once per year. its also a good time to check the muffler and the jet impeller wear ring clearence.

Re: Over Heating Problems

Hello Rodbolt- some time ago you guided me thru some overheating problems w/ my Yamaha 150 OB Jet. 1K in the shop took care of that but now with several people in the boat (under load) I ca'nt get any more thrust at 25K RPM than at 50K RPM, the jet impeller is set properly & the bowl is new. Someone on this forum once mentioned loss thrust via the exhaust tube? Any suggestions.

Re: Over Heating Problems

if the exhaust tube corrodes a hole in it it allows water pressure to enter the exhaust cavity and will slow the engine down. everything will test good but it wont run correctly. has burned many a tech. use a flash light and look down the tube. it usually rusts at the aluminium housing. it also may be that the weight is to much. the impeller to wear ring clearence is about .03". its hard to check but not impossible. could be its to much clearence. could also be the impeller is the wrong pitch. could also be the grate is to low in the water and dragging or to high and cavitating. if your RPM is the same and the hull speed slows down its either overloaded or cavitating. the cooling water pump draws water from the jet. to much cavitation and it feeds air bubbles to the cooling system.<br /> sorry to anyone I have been grumpy with but at least I still try to help out

Re: Over Heating Problems

thanks - I'll look into those suggestions. It's bizzare, although the load never changed, in the 1st part of the day I had no problem getting up on plane & good hull speed.... an hour later, plenty of RPMs - no speed