tohatsu still overheating?

[Jizm]

This may help

[slimtim]

Ben, thanks.

Had a look over the engine tonight.

Plugs: The white bit around the middle is in fact brown. The bent bit on top and the ring around the edge is lightly covered in a black soot/oil. See pic below...any thoughts on what this might indicate? I reckon I had the mixture too rich as the screws were about 2.25turns out.

I cleaned the plugs and set the mixture screws to 1.5turns out. She started from cold with no idle and just choke, but quickly warmed up to what I think is too hot! Anyway, I left it a while and no water (only spitting) came out of the hole below the cowling as ben suggested...but it poored out of the outlets I have highlighted in the pic.

I took out the thermostat and as I took the cover off, a whisper of steam came out. I re-tested it in near boiling water and it seemed to work fine. Then when I reduced the water temp (but still too hot to put fingers in for more than a split second) it failed to open very much at all. I'm sure the water should be getting to near boiling inside the engine before the thermostat opens??!!

I re-ran the motor without the thermostat in and it ran very cool and with a slightly weaker tell tail...as I guess a lot of water was being diverted down the leg instead.

So, as far as I can tell, there is no blockage anywhere as it stays cool when I run it without the thermostat. Now I would have thought the thermostat would either work properly, or not work at all, not somewhere in between...any thoughts?

Thanks

Tim

[jwalker]

The spark plug insulator colour looks about right considering you've been running the engine slowly. Tan is the colour you are looking for when the mixture is correct and the temp is correct. If the mixture is too weak, the insulator will be pale.

The thermostat can, and they frequently do, start to open at an incorrect temperature.

[Nasher]

Tim

I have a non contact (infrared) temperature measuring 'gun' that you can borrow if you like.

Or I'm thinking of taking a run over to the Island later this week in my boat with my kids so perhaps we could meet up.

Its a good(expensive) piece of kit, but easy to use, and will give you quite an accurate temperature of your engine block. Its not unfortunatly very good on still or running water as you can't adjust the Emissivity Value on it.

You or I could also 'measure' a couple of other engines to compare.

I've used it before to find out which pot was giving me trouble on my fuel injected bike by comparing the exhaust header temps, and have also used it to take the kids temperature when they've been off colour.

The plugs look OK to me, one is a nice tan colour and the other isn't too bad.
Thermostats are Black Magic, and seem to open at whatever temperature they feel like on the day.

Nasher.

[LURCHER]

I have just had a similar problem with my Optimax ,a good tell tale flow was seen coming from the engine yet engine temp would climb rapidly at low revs untill Gaurdian cut in ad reduced revs ,the motor then had to be stopped and restarted and revs increased to get water flowing through to cool it down . A high revs it was fine but had the problem at 1500 - 2100 rpm .We changed 2 thermostats and a poppit valve blew out all the waterways and still had the same problem . We had fitted a new impellor in the spring so had not changed that . Cut a long story short as a last resort we put in a new impellor and wear plate which looked exactly the same condition as the old ones and problem solved. What a long way round to a simple fix !

[slimtim]

Someone mentioned earlier that their thermostat opened at a cool enough temp to allow them to dip their fingers in the water. Mine would only empty at near boiling! I'm sure this can't be right. Is it possible for an old thermostat to get sticky and therefore require more heat to open it sufficiently? Is getting a new thermostat the best cause of action I can take at this time?

Will screwing the mixtures screws in increase my revs at idle? She was running at about 1500rpm at idle on the muffs yesterday, which is obviously more than it should be and more than it was before (even taking into account the reduction in rpm you get with the back pressure of the water on the exhaust). I guess I need to readjust my idle screw to settle her down to 800-900rpm.

Thansk for all your help so far.


Tim

[Nos4r2]

Originally Posted by slimtim

Will screwing the mixtures screws in increase my revs at idle? She was running at about 1500rpm at idle on the muffs yesterday, which is obviously more than it should be and more than it was before (even taking into account the reduction in rpm you get with the back pressure of the water on the exhaust). I guess I need to readjust my idle screw to settle her down to 800-900rpm.

Thansk for all your help so far.


Tim

Might do-depending on what the mixture screws control. Some control air, others control fuel depending on your particular carbs.

I'd follow Fred's advice-do up the mixture screws til they seat lightly. Turn ONE out by 1.25-1.5 turns. Bring the other out to 1 turn and then turn it outwards til you get a smooth idle. (this should work with less than an extra half turn). Your idle speed will be about right as long as you follow this as long as your throttle is adjusted right. If idle is too high/low after setting the mixtures then adjust the tickover rather than the mixtures.

If your manual says a different number of turns use that number, but the principle is still the same.

[slimtim]

ok thanks...my engine is 3 cylinder by the way! I need to get me one of those engine manuals I think.

I have found that my thermostat's operating temp is 60deg, as it has it stamped on it in incredibly difficult to read writing. I think 60deg should be cool enough to stick my fingers in shouldn't it?

I'm waiting for a price for a new thermostat, in the mean time I may just run it without the thermostat installed and apparently use a bit more fuel

Tim

[Searider]

Tim,

My Optimax runs at any temperature from about 45C when running fast to about 65C when running slowly, with an occasional overheat alarm (80C) when going at the wrong speed on the river.

Raw water cooled engines tend to run much cooler than fresh water engines as if they run over 60C there is a tendancy for the salt to crystalise on the waterways.

I would guess that a thermostat for a raw water cooled engine should be fully open by about 60 ish C.

If your thermostat needs the water to be almost boiling before it opens I would suggest that that is where the problem lies.

Stick a new thermostat in and see what happens.

[Scary Des]

Originally Posted by slimtim

...... I think 60deg should be cool enough to stick my fingers in shouldn't it?.....

would hurt my hands, but I'm very delicate , anti- scald devices have a top setting of about 50C but it is subjective, if you have fingers like leather sausages you probably wouldn’t notice.
Tim you must get some way of measuring temperature, otherwise you are only guessing.
With your thermostat you should check its opening temp against a thermometer then you will know for sure if it is working right. Des

[slimtim]

nasher, thanks very much for the offer. If I can't sort it soon, I will take you up on that!

I'll try and get a temp tonight at which the thermo opens, that'll give me a better idea of whats going on.

Thanks

Tim

(Duncan, Warshot was looking good on sunday )

[Hightower]

Can you hold your hand under your hot tap for any length of time as that'll be roughly 60 Deg.

Looking at the diamgram Jizm showed earlier the tell tail is after the thermostat. If this was the case you'd only get water out of there after normal operating temp was reached. I'm sure mine has a Y piece some where that takes water from both the pump and block?

Tim, an investment in a new thermostat might be in order. Do they do different temp ranges like in cars (Winter and Summer)?

[slimtim]

hi andy,

That diagram is not the same as my outboard I don't think. On mine, the water is pumped up to the thermostat where, it can either flow down the side of the block to the tell tail exit (when the thermostat is closed) or flow down there and down the end of the block around the plugs and then I assume out of the outlets at the bottom of the leg (when the thermostat is open)...hence why if I run it without a thermostat, excess water flows down the end of the block and out the bottom leaving only a small ish amount to flow down the side and out of the tell tail. This is all an assumption as I've only been able to look at the engine from the outside.

New thermostat is £32.50+VAT+carriage I'm going to double check mine with a thermometer before ordering. I'm not sure they do ones for different temps.

Cheers

Tim

[Jizm]

Tim, andy
you're both right! That diagram is wrong for a typical outboard,didn't notice until you pointed it out. Water comes from the pump up the leg and has a T piece for the tell tale. When hot enough the stat opens letting hot water out of the motor beneath the cowl and allowing cool water in from the base of the leg.

Tim mine opens at about 60deg and the water is not too hot for me to stand (asbestos hands tho'). You really want to run the motor in a large bin as the motor can pump more water than a hose can supply. Does sound like your stat is duff tho'.

[slimtim]

Ok, tested my 'stat tonight and she didn't open at just over 60deg, but did at about 80deg (not fully though I don't think). I will order a new one tomorrow and hope that that solves the problem!

Tim

[Jizm]

Did the new stat solve the problem mate?

[slimtim]

yeah i think so cheers ben. I've had the carbs cleaned out too and runs much better (although still often needs some throttle to start).