1999 200 OX66 --- Overheating Issues/Repairs

[TownsendsFJR1300]

I have the identical problem. 1999 Ox66 overheats over 4000 rpm. New water pump assembly. New stats. New temp switches. New PRV updated version. Runs all day under 4000 rpms. Temp alarm goes off, motor shuts down to 1200 rpm. Let cool for 1 minute. No alarm. Used laser temp gun. Can find anywhere on motor over 150 degrees. Where is this screen located by the PRV? Next heads come off. Appreciate your help.

Don't know about the screen, but, unless your religious about flushing immediatly after salt water/brackish use, your probably going to find a bad build up of salt water deposites around the cyljnder coolant passages and the head.

If using a lazer temp gun, (we did NOT), point at the lower BLOCK/cylinders/water jacket, near the head, especially the lower 2 cylinders on each side and compare temps higher up the block.

We had the same issue with my neighbors v6 200. (he didn't flush regularly, if at all). The lower two cylinders were about 90% clogged with hardened salt, thus, almost no water flow (which happened to be near the sensors). After cleaning 3.5" of salt out, ran like a scalded dog, no shut downs.

BTW, these links may be helpfull and worth a read;

http://www.yamahaoutboardparts.com/f...g-th19434.html

http://www.yamahaoutboardparts.com/f...m-th23666.html


Good luck and please post you findings/fix...

[Livinlinelife]

If u remove your thermostats and you don't reach operating temp your fuel efficiency will SUCK, literally!

[99yam40]

If people would stop posting trying to help when they post on very old threads maybe they would get the message,
Just tell them to start their own thread

[Tucker]

I'd let it run in tub of salt-away first. Pull head as last resort. Those head bolts tend to snap on these old girls.

[TownsendsFJR1300]

I think his was about a 2000 model, corrosion quite obvious under the cowl...

Didn't have one fastener break, just lucky I guess...

[bajakeith]

Seen this TOO many times

why o why does every guy think he is a marine tech !! the seal above the w/p cup and the seal "o ring" on the botom are very tricky to install correctly !!! I have seen Soo many torn,ripped bottom o rings and even missing top o ring missing....they don't pump well at high rpms and actually suck air (exhaust) and overheat...also the there is a proper way to set the impeller "height" and wavy washer with the locking collar......Sigh...

[TownsendsFJR1300]

i have the identical problem. 1999 ox66 overheats over 4000 rpm. New water pump assembly. New stats. New temp switches. New prv updated version. Runs all day under 4000 rpms. Temp alarm goes off, motor shuts down to 1200 rpm. Let cool for 1 minute. No alarm. Used laser temp gun. Can find anywhere on motor over 150 degrees. Where is this screen located by the prv? Next heads come off. Appreciate your help.

any updates???

[rodbolt17]

sorry, there is no impeller "height" setting.
your setting a bearing preload to keep a knocking noise to a minimum at low speed.
leave out the wave washer assy and it has no affect other than it can develop an annoying knocking noise at low speeds.
wont hurt anything its just annoying.

that rubber dam below the wearplate,if corrosion lifts it up and its not addressed then at reassembly it leaks a bit of air causing low speed overtemps.

[bajakeith]

impeller height

Yep,,You tell it in a better way than me !! if yammy cut the gears different there would be no reason this,,,like the older mercurys with the preload pin !!!

[rodbolt17]

and why do you think they had the preload pin?
to keep the knocking down.