questions about possible thermostat problem????

M

masilobes

Member
Nov 2, 2010
81
buzzards bay ma
Boat Info
Kayla B
Engines
twin 350 mag mpi
2003 280 sundancer 4.3 mpi's. ran great all day yesterday, on the way home ran for about 30 min at about 3600 rpm. last mile home, bumped it up to 4000 and port motor went to 200 and alarm sounded for high temp. stopped, took it out of gear. alarm stopped. started going again at 3600 and came right down to 170 like it alwys has run. could this be a bad thermostat? water pumps and manifolds and risers all new this spring did this once idling at my mooring, revved it up and temp came right back down. any ideas?? thanks
 
Your symptoms pointed to you running over debris / weeds that got stuck on the port drive over the intake and floated away when you stopped until you said this…

masilobes said:
......... did this once idling at my mooring, revved it up and temp came right back down. any ideas?? thanks
Click to expand...

Please give us more explanation of the above.


Just for what it’s worth, a bad impeller causes overheating at low speed or idling, not on plane. Once you are on plane the flow of water will cause circulation similar to your cars fan is just along for the ride at highway speed as air flows past your radiator.

Just to confirm, we are talking about a raw water cooled engine, right? So the issue is water circulation restriction.
 
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yes raw water cooled. water pumps and impellars are new. the time in question, i was out for awhile cruising 3500 rpm for about 45 minutes and when i got to my mooring I left it idling while i did my lines and tied off for the night. when i returned to the helm, port motor temp was rising to almost 200. i revved it up in nuetral and it instantly came back to 170. hasen't done it since. this time like i said i was cruising back at 3500 and for the last mile or so i bumped it up to about 4000 and it climbed up to 200 and the alarm sounded. took it out of gear alarm went off and i started up on plane again and it dropped back to 170. so i dont know. i was just thinking a stuck thermostat maybe? revving it up just forced the issue? and got it open??
 
Replacing a thermostat is fairly easy and cheap. You should replace it just to remove it from consideration. That being said, in my experience thge thermostat either works or it doesn't. It wouldn't result in a sporadic problem.
 
I am also having the same issue with a 5.0 BIII motor. What is the limiting factor of the incoming water? Where are the water restrictions?
 
solved my problem!! i guess the $80 a quart trilux was a waste because already the drives were covered in small barnicles. the water is still alittle cold so until yesterday when i got in and looked i was pissed. they brushed right off but i guess on the port drive they were covering the intake just enough that at higher speeds water wasnt flowing like it should have been. the temp went high and set the alarn off again on the way to bassets island, cleaned them while there, and ran all the way home at 4000 and ran at 170 the whole way no alarms she ran great!! jeffk... this doesnt help you i dont think because on the bravo 3's the intake is not in the drive leg, however the intake on the hull could need to be cleaned. good luck
 
I have intakes on the outdrives. I am assuming I may have a restriction betwen the outdrive and waterpump. Any way of clearing "Tubitus" other than pulling the motor to change this tube?
 
Pulled the red water intake hose off the water pump and hooked it to a water hose. Then ran Salt away back out the drive while poking the intake water holes on the drive. Ran it up the other day, and it seemed better, but didn't run quite as low as the other motor. So I may still have some intake restriction going on there. Has anyone replaced the red intake hose without pulling the motor?
 
the small hose visable outside the boat that runs from the drive to the transom assy is usually the problem - i fixed mine by removing that hose, blocking off the inlet (merc sells kit) and putting in thru hulls/strainers - no problems since.
 
Nice, do you have the kit number? I want to look into this. Is it a DIY job? What was the extent of the project????
 
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Has anybody else used this external water inlet source? I want more info on it, and may install it.
 
Turns out it was the hose, full of barnacles. Id like to Install the thru hulls and strainers
 
I do not have the kit number, but we found it in a merc catalog - all it is is a block off plate that covers the opening when you remove the "water neck" that the sea water hose attaches to. access is tuff as these are on top of the transom assys inside the boat (you must lay on top of the motors - the side with the steering ram is even more restricted) Once that is done you MUST remove a section of the "transfer hose" outside the boat - this runs fron the drive to the transom assy. It is right up agenst the u-joint bellows so BE CAREFUL! the pupose of removing this section of hose is so the drive will continue to ge flow through cooling - if you just deadhead the hose with the plate inside the boat, the drive will not cool.

From there it is a simple matter of using off the shelf scoops, seacoks, strainers, and hose much like any inboard boat has - the 300 da already has faring blocks in the hull and a handy place to mount the strainers (I put mine at the corner where the "shelf" meets the stringers). The most difficult (at least psycoligally) part is cutting the holes in the bottom of your boat!
 
Thanks, do you have any pictures of this install? Is there a difference in materials? Bronze or composite? There is a big price difference.
 
It's a shot in the dark, but I once had a poppet valve hang up when a piece of scale managed to get stuck in it and the engine overheated. Fortunately the side that didn't get its share of cooling water was the same side as the sensor (why both sides weren't 'sensed' puzzled and 'incensed' this owner). If the problem cleared you may have picked up something soft that temporarily interrupted the cooling water flow. Intermittent problems are the hardest to diagnose. Good Luck! -- Frostman
 
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