Optimax 200 overheating specific conditions

[Flounder89]

I have a 07 Optimax 200hp I bought used a few months ago and have been dealing with an overheat issue. Runs normal temp through all rpm ranges, and if the motors cool when I crank it the temps stay normal, will hit 129 on vessel view and the t stays open and it drops some and cycles back to 129. I can run it to the normal operating temps and then kick it into neutral and the temps stay normal, but if I get it up to running temps and shut the motor down for a few minutes when I crank it back up the temps run up high unless I idle it up to around 1500 rpm’s in which case they drop right back down and it’s fine to idle again. I have noticed it takes a while to start peeing again when I crank back up, unless I idle it up then it’ll start to pee relatively quick. I have two new thermostats in it, and a new water pump kit, cleaned strainer and flushed motor out. Runs great all the time except for right after cranking back up, I’m at a loss of what else to try.

 

[Chris1956]

Let me see if I understand. It runs fine, but the gauge shows overheat, when restarting after a short shutdown.

Sounds like heatsoak. You have a warm motor. You shut it down, and the cooling water drains out of it. Residual heat causes it to show a hot reading.

Does it run fine after restart? Run it a couple of minutes before shutting it down and see if that helps.

 

[Flounder89]

Yes after a short shutdown when I crank it, it’ll will sound a constant alarm after a minute maybe, and I’ve confirmed with vessel view that it is running up to a high temp. It will run fine, soon as I put it in gear and start to take off the alarm goes off and temp drops back down to 120ish and stays there. Once I’ve got it cool I can put it back into neutral and temp stays normal. Only happens on start up once motors warmed up

 

[Chris1956]

You didn't mention any repairs of the poppit valve. That probably merits an inspection at least. If the poppit valve was sticky, it can cause everything from mild overheat to major overheat.

 

[Flounder89]

Chris I have pulled the poppit, I replaced the diaphragm and gaskets. When I pulled it I found the seal was half way unseated letting a ton of water by, I figured that was my problem when I seen it, but it did not fix it. It has been better since I fixed that. Doesn’t try to run hot on every crank up since, sometimes I can crank and idle and watch them temp rise to 150-160 and fall. Other times it’ll run right up to 185 if I don’t idle up or put it in gear and go.

 

[Chris1956]

Still strange behavior. The only suggestion is a possible workaround.

Those Merc impellers can get some damage to their bases. This causes less volume to be pumped on idle, and they can overheat. Higher speed pumping is fine. If you are sure the impeller is good, this isn't the issue.

Compression leaks at the cylinder head cause overheat at high speed. They are high RPM-specific.

Finally the possible workaround. When you are at idle and ready to shut the engine off, run her at fast idle for a minute to remove any residual head. Your poppit should open at 2000RPM, but keep the RPMs to no more than 1500, and the 'stats should cool her off.

Best I can think of at the moment.

 

[Flounder89]

Yeah it’s got a brand new water pump kit in it, I replaced everything. Has probably an hour on it. I’m not sure what else to try and change. I pulled poppit again yesterday to make sure the seal hadn’t come back out, because it went for probably 5 start ups just fine then started to overheat again. I figured it was back unseated but it wasn’t. Like you said I can work around it, if I idle up to about 1500 rpm on start up and hold it there for maybe 15-30 seconds it never gets about 130. I just hate to not have everything running like it should, this just has me at the point I’m not sure what direction to go with it.

 

[Flounder89]

Also, it never overheats at high idle, runs perfect. About two weeks ago I did have to pull my starboard side head because I had an air injector get stuck and break off when I tried to pull them to send them out for cleaning. So one side does have new head gasket. I’ve also flushed it several times and several different ways, get plenty of flow every which way.

 

[Faztbullet]

That motor doesn't have a water pump base.... make sure filler block is in place in lower unit. and has the correct t-stats and matching covers. Also check you air pump as it has a temp sensor on it.

https://holesbaymarine.co.uk/catalog/media/F53DEL3GOJSW4Y3INVQXE2LOMUXW2ZLENFQS6YTNMUXUOQKZIRBVQQSRI5HE6RCFJVBFCR2KJ5CUWVCTG5DUCNCBFZYGIZQ

 

[Flounder89]

That motor doesn't have a water pump base.... make sure filler block is in place in lower unit. and has the correct t-stats and matching covers. Also check you air pump as it has a temp sensor on it.

https://holesbaymarine.co.uk/catalog/media/F53DEL3GOJSW4Y3INVQXE2LOMUXW2ZLENFQS6YTNMUXUOQKZIRBVQQSRI5HE6RCFJVBFCR2KJ5CUWVCTG5DUCNCBFZYGIZQ

I’ve got two new 130 t-stats in it, I’ll check the covers today though. I’m not sure that I have the new style in the link. I’ll also drop my lower unit and check everything on the pump again just to be certain. What exactly should I check on the air pump? I’ve cleaned the strainer but that’s it, I wasn’t sure what else I could do for it.

 

[Flounder89]

What exactly is the filler block? Want to make sure I’m looking for the right thing. I have the diagram of the lower unit to go off of but not certain I’m looking for right thing

 

[Faztbullet]

Number 3...

 

[Chris1956]

Actually I said impeller base. If the impeller base gets some damage, the Mercs will overheat at idle, but run cool at high idle and faster.

 

[Faztbullet]

It has no base..2 gaskets and wear plate the bolt directly to lower unit housing..

 

[Chris1956]

Right, no pump base. I get it.

The impeller has a bottom, sometimes called the base of the impeller. If that rubber takes some damage, the motor can overheat at idle and cool fine at high idle and higher RPM.

 

[Faztbullet]

Not likely with a floppy vane impeller