Reply
 
Thread Tools Search this Thread
 
Old 18 July 2006, 16:06   #21
RIBnet supporter
 
Jizm's Avatar
 
Country: UK - England
Town: Southampton
Boat name: Hissing Sid
Make: Ross Smith Cobra
Length: 6m +
Engine: 200HP Optimax
MMSI: 235038046
Join Date: Jun 2002
Posts: 3,803
This may help
Attached Thumbnails
Click image for larger version

Name:	obcooling.JPG
Views:	210
Size:	20.0 KB
ID:	21006  
__________________

Jizm is offline   Reply With Quote
Old 18 July 2006, 18:07   #22
Member
 
Country: UK - England
Town: I.O.W/Bristol
Boat name: HotShot
Make: shakey
Length: 5m +
Engine: 70hp Tohatsu
Join Date: Jul 2003
Posts: 1,543
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
Attached Thumbnails
Click image for larger version

Name:	plug1.jpg
Views:	142
Size:	77.6 KB
ID:	21009   Click image for larger version

Name:	plug2.jpg
Views:	145
Size:	82.4 KB
ID:	21010   Click image for larger version

Name:	outboard.jpg
Views:	155
Size:	96.7 KB
ID:	21011  
__________________

__________________
slimtim is offline   Reply With Quote
Old 18 July 2006, 18:44   #23
Member
 
Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,962
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.
__________________
JW.
jwalker is offline   Reply With Quote
Old 18 July 2006, 18:46   #24
Member
 
Nasher's Avatar
 
Country: Other
Town: Principalite d'Chaos
Boat name: The Nashers Revenge!
Make: Ocean & Bombard
Length: 6m +
Engine: Suzi DT200EFI, DT9.9
MMSI: "Mmmmm SI" she said!
Join Date: Jan 2004
Posts: 4,147
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.
__________________
RIBBED For extra pleasure.
Member of the ebay Blue RIB cover club.
Member of the Bombard 380 Aerotec club
Nasher is offline   Reply With Quote
Old 19 July 2006, 01:47   #25
RIBnet supporter
 
LURCHER's Avatar
 
Country: UK - England
Town: Tisted Hampshire
Boat name: Hot Lemon
Make: Scorpion
Length: 8m +
Engine: Inboard
MMSI: 235
Join Date: May 2002
Posts: 766
Send a message via MSN to LURCHER
Overheat

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 !
__________________
www.hiremarquee.co.uk
LURCHER is offline   Reply With Quote
Old 19 July 2006, 03:46   #26
Member
 
Country: UK - England
Town: I.O.W/Bristol
Boat name: HotShot
Make: shakey
Length: 5m +
Engine: 70hp Tohatsu
Join Date: Jul 2003
Posts: 1,543
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
__________________
slimtim is offline   Reply With Quote
Old 19 July 2006, 04:05   #27
RIBnet admin team
 
Nos4r2's Avatar
 
Country: UK - England
Town: The wilds of Wiltshire
Boat name: WhiteNoise/Dominator
Make: Ballistic 7.8/SR5.4
Length: 7m +
Engine: Opti 225/Yam 85
MMSI: 235090687/235055163
Join Date: Jul 2005
Posts: 12,645
RIBase
Quote:
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.
__________________
Need spares,consoles,consumables,hire,training or even a new boat?

Please click HERE and HERE and support our Trade Members.

Join up as a Trade member or Supporter HERE
Nos4r2 is offline   Reply With Quote
Old 19 July 2006, 04:30   #28
Member
 
Country: UK - England
Town: I.O.W/Bristol
Boat name: HotShot
Make: shakey
Length: 5m +
Engine: 70hp Tohatsu
Join Date: Jul 2003
Posts: 1,543
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
__________________
slimtim is offline   Reply With Quote
Old 19 July 2006, 04:33   #29
Member
 
Country: UK - England
Town: Southampton
Boat name: SMH Rib / War Shot
Make: Ribtec / Scorpion
Length: 4m +
Engine: 10hp Yam / 150hp opt
Join Date: Sep 2003
Posts: 1,894
RIBase
Running temperatures / thermostats

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.
__________________
Searider is offline   Reply With Quote
Old 19 July 2006, 04:51   #30
Member
 
Country: UK - England
Town: nr Lymington
Boat name: JU-JU
Make: Halmatic PAC22
Length: 6m +
Engine: 140.5 Mermaid
Join Date: Sep 2003
Posts: 1,400
Quote:
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
__________________

__________________
Scary Des is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 03:01.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.