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20 hp tohatsu 4 stroke overheat

skloak

New member
i noticed that this subject had been noted before, i would like to see how to avoid it in the future. i too had an oil cap blow off due to an over heat of my 20 horse tohatsu. i live in south texas and fish in the lower laguna madre, salt water, i was running shallow but not too, however, we are having extreme amounts of floating grass this year, and i think this was the culprit of my over heat. i have it now at the dealer and they are waiting for a part, two weeks now, from japan in order to get me going. they said that all looks to be in order. they opened the whole back half of the motor and said that all looks well inside. i feel a little unsure, however; i dont want this to happen again!!!! is there a water temp guage i can get for this little motor to help with this in the future? what else can i do to avoid this happening again? since i got this little 20 horse, i have had nothing but problem with it. carberation, sluggish, cowling keeps coming off, seal on cowling allows water under the cowling and saltwater all over the motor. any suggestions would be great!!!!
back to the oil cap issue, i had checked my oil and had to add some at one point. it was then that i noticed the oil cap had already been melted to some degree in the past, i am a second owner, so i had been watching it very closlely when this over heat happened. i am also experiencing a lot of surging after i have been running for quite a while. much like i have a spun hub on the prop. put another prop on it and after running a while i shut down to fish. when i take off again, it is then that is will begin to surge. it doesn't do it on the enitial run from the ramp to the first stop. i am thinking this also may be due to grass.

sorry for all the confused problem sharing, i am just so frustrated with this motor. thanks so much in advance for your advice, skloak
 
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The motor will tell you when it is overheating. Pay attention to the owner's manual. Yes, you can add a water pressure gauge, but nobody does. Only a SEVERE overheat would melt plastic parts on the motor. That's classified as abuse by most dealers. What is your exact model/serial? Are you in the 3-yr warranty? There is a replacement gasket for the cowl, if yours is shot. You may also have a carb problem, causing issues, assuming everything else (temp, etc.,) is OK. Do you run the carb dry at the end of every day?
 
This is not an engine problem...This is an customer operation problem. You need to keep an eye on the pee indicator when running your engine in adverse condtions. That's what it is for. The oil caps are available and are in stock. The surging could be anything at this point and would require a dealer to pinpoint the reason. The engine should be in warranty and your local dealer should be taking care of all of this for you.
 
I was watching the pee hole and it never stopped peeing! I am very carefull with the motor cause I can't afford all this extra! I have had other outboards in my life and have always taken care of them the same and never had any problems!
 
I believe you...But, if you overheated due to grass, then the engine must have stopped peeing at some point. Regardless, you still need to let your local dealer look at the engine, make a determination as to the problem and let them fix it.
 
its been at the dealer about two weeks now, he said something about going through warrenty, but never heard anything else. the cap is in customs coming from japan, no one seems to have any around here. i was wondering if a cap from another brand would fit. the dealer said yes, but didn't offer to find one. the dealer has gone through the motor, took the whole back half appart and said that all looked well. i am just scared it will happen again. i am constantly looking back to make sure it is peeing, and it is. as to the cowl gasket, the dealer has looked at it and all the issues i have mentioned. they say that the gasket is fine and now are saying that it is due to bad desine of the clasp on the back. i am just so tired of not being able to go many many trips without problems like i have with so many other motors in the past. thanks for your replies, i think i am going to trade the guy i sold my 15 yamaha and get it back. it was in beautiful shape, just sitting in my garage so i felt bad it not being used, live and learn i guess. thanks again.
 
I have a couple of those filler plugs on the shelf, because sometimes someone will drop one overboard. Your dealer can call me at 716-877-8221 and I can drop one in the mail if they'd like... They are currently out of stock at the US distributor's warehouse. The ONLY way for one of those to melt is an overheat so severe that lesser motors would warp a head -- or worse. We're talking so bloody hot that you could cook breakfast on the motor. There is NO WAY that the motor did not stop peeing for quite a while to cause that level of abuse. Period. The forensic evidence tells the story. And if that filler plug has melted, there may well be other plastic bits that have been melted, so the entire motor should be checked over for signs of severe overheating. I would also do a compression test to verify that there isn't any internal damage, such as a burned piston, burned exhaust valve or a warped block or head.

If some mutton-fisted operator tried to jam and slam the latch closed when the cowl was not seated correctly, and hence damaged the latch, you may need a new one. If the cowl seal has been damaged, that should be changed as well.

Once the motor has been repaired, you should be OK. But you still need to ensure that you don't starve the water intakes with grass or other debris, or you could overheat any motor of any brand just as easily. The MFS20C has a water strainer located on the underside of the ventilation plate, called the sub water inlet, so if running too shallow, even though the prop and lower water strainers are mostly in the water, you could be so shallow that the upper strainer is sucking air. That will damage the water pump, and will overheat the motor. That overheat condition could be the cause of your surging.
 
thanks, paul for everything. i am really excited to see how it turns out with the new thermostate and everything else we are doing to it. i am going to keep working on all the rusted bolts etc. until i get the thing in the kind of shape i want it to be in. the dealer and his tech tell me that it is a really good motor and that this is just something we got to get past. i was looking at the motor and i have seen some that overheated in the past. none of the paint is bubbled, all the plastic and rubber parts are in good shape. the dealer said that he and the tech went through all that as well as the carbs, gave it a good study. now with the thermostate changed, i feel a little better. the stat was in really bad shape. from now on, along with the oil, water pump, lower unit fluid change that i do every summer, i am going to include a new stat as well. thanks again for your help, steve.
 
Steve, I hope it all works out for you. Our bookkeeper took the package to the post office (thinking, as I did, that it would be less expensive to ship the puny 2-ounce package that way)... and I have to tell you that he goofed. I told him that you'd like the parts for the weekend... so he shipped it with Saturday delivery... Hopefully your shop is open on Saturday! Because he shipped it that way, the postage alone is as much as you paid for the whole order :(
 
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