optimax tstats not opening quick enough

[robaloroger]

I have a 2000 optimax 225 with 120 degree t stats 850279-2. My motor was over heating so I removed the t stats and tested them. The book said they should start to open between 188-122 if not discard them. They were starting to open at 135 degrees so i ordered 2 new ones. Got them and tested them and they start to open at 135 also. I tested them with fast rising heat and slow rising heat and both the same. So either the old t stats are good or the new ones are bad. either way I wasted $75. Are these t stats bad? Anyone test any t stats that open within the range they say they should?

 

[jerryjerry05]

Re: optimax tstats not opening quick enough

Sounds like you wasted $75 If your overheating and the thermostats are opening then your in the wrong area.If they are bad then they usually won't open.
Sounds like the impeller should be the first thing you change.Then get a diagram of the cooling system and start looking into that.J

 

[jeffersondodson561]

Re: optimax tstats not opening quick enough

If you replaced with different tstats you are going to be running rich from now on. The ECM takes temperture reading to calculate for fuel map. Check the Pressure Relief Valve, if it is leaking pressure will not build up in the block and tstats are ineffective good to have a manual for this. Once corrected put the original tstats back in.

 

[Faztbullet]

Re: optimax tstats not opening quick enough

If your engine falls in the OT409XXX thru OT598999 it needs the t-stat update kit. There is a SB issued on this and the kit has 2 -130 degree stats and 2 newer covers. I dont think stats are your problem.

If you replaced with different tstats you are going to be running rich from now on

Only if its running cold at low rpm.....

 

[robaloroger]

Re: optimax tstats not opening quick enough

Thanks for the replies guys. I was not sure the tstats were the cause of the overheating but it says in the merc manual to replace them if they do not start to open between 118-122. I figured that tstats are bad if 1. they dont open or 2. they dont open within the specified range. Maybe the tstats should be 135 degree instead of 120 degrees. Does not make sense to me.
Faztbullet, the sticker was peeled on the motor when painted so I dont know the serial #. I think it is stamped on the powerhead somewhere. I will have to check into the update kit. The previous owner said the impeller is 6 months old but I am going to change it out over the weekend anyways. My main question should be.. Would tstats opening at 135 instead of 118-122 cause rpm reduction and alarm?

 

[robaloroger]

Re: optimax tstats not opening quick enough

anyone know if the alarm could be sounding because the tstats are opening at 135 degrees rather then 120?

 

[jigmister1]

Re: optimax tstats not opening quick enough

No. they alarm will not sound until the engine reaches near a dangerous temprature.

 

[starcraft1982]

Re: optimax tstats not opening quick enough

Ok,I dont seee where you mentioned if its "peeing" properly or not.Dont be so quick to assume t-stats.Waterpump should be rebuilt every 4 yrs.Impeller replaced every 2(both minimums).Previous owner may have never had pump rebuilt.If youre going to do the impeller just get a rebuild kit and replace the gaskets while youre at it.Also inspect the "cup"the impeller sits in.If its grooved at all,it needs replaced alslder motors have a poppet valve.Not sure yours has it but i would think so.Anyways,it opens at higher rpms to allow more water through to cool the motor since it needs more at higher rpms.t stats control water flow at idle/low rpms.Any could be culprit.Does it do this at idle(overheat) or while running?Peeing any?stream or trickle?Just saying that not all overheating is "automatic"impeller or t-stats.

 

[robaloroger]

Re: optimax tstats not opening quick enough

Ok,I dont seee where you mentioned if its "peeing" properly or not.Dont be so quick to assume t-stats.Waterpump should be rebuilt every 4 yrs.Impeller replaced every 2(both minimums).Previous owner may have never had pump rebuilt.If youre going to do the impeller just get a rebuild kit and replace the gaskets while youre at it.Also inspect the "cup"the impeller sits in.If its grooved at all,it needs replaced alslder motors have a poppet valve.Not sure yours has it but i would think so.Anyways,it opens at higher rpms to allow more water through to cool the motor since it needs more at higher rpms.t stats control water flow at idle/low rpms.Any could be culprit.Does it do this at idle(overheat) or while running?Peeing any?stream or trickle?Just saying that not all overheating is "automatic"impeller or t-stats.

Thanks for the responce.
The previous owner said the impeller was 6-9 months old. I checked it out and it looked good but I replaced it anyways. I checked the strainer to the air compressor and it was not clogged. I blew compressed air through just about all the hoses I could access. The motor was overheating at 1500 rpms after about 10 min. My motor does have poppet valves but I did not mess with them because it is overheating at low rpms.I am not assuming tstats but the tstats are not opening at the specified temp. The new tstats are not opening at specified temp either. I am going by the manual. I dont know if I should try to find 120 tstats that start to open at 120 degrees or if I should assume it is not the tstats. The only thing that does not seem right is the tstats and that is why I am asking about them. I dont know why 120s would open at 135 when the book says replace if they do not start to open between 118-122. Maybe 110s would open around 120?

 

[starcraft1982]

Re: optimax tstats not opening quick enough

Gotcha.I didnt see where it was happening at 1500rpms.I will ask one more thing to maybe provide info for "the knowledgeable".What temp is the alarm sounding?now you should shut down immediately if alarm sounds,but what is it reading?Any way you have access to a digital point/shoot thermometer to get temp of heads?Just saying that even if thermostats arent opening until 135 or so,Ive never seen an alarm that sounds that quickly.Usually it would have to get over 160 or even 180 before alarm would sound.So if theyre opening and its still climbing enough to sound the alarm(provided higher temp is needed)the t stats wouldnt be the problem.Well,thats it for me.I`ll let someone who can help you better chime in.Best of luck.

 

[CharlieB]

Re: optimax tstats not opening quick enough

Have you checked compression to verify the integrity of the head gaskets?

Even a 10% difference in one cyl could indicate a small leak which will allow combustion gases to blow into the cooling system, displacing water, and cause an overheat.

Check compression carefully, write each reading down.

 

[robaloroger]

Re: optimax tstats not opening quick enough

Gotcha.I didnt see where it was happening at 1500rpms.I will ask one more thing to maybe provide info for "the knowledgeable".What temp is the alarm sounding?now you should shut down immediately if alarm sounds,but what is it reading?Any way you have access to a digital point/shoot thermometer to get temp of heads?Just saying that even if thermostats arent opening until 135 or so,Ive never seen an alarm that sounds that quickly.Usually it would have to get over 160 or even 180 before alarm would sound.So if theyre opening and its still climbing enough to sound the alarm(provided higher temp is needed)the t stats wouldnt be the problem.Well,thats it for me.I`ll let someone who can help you better chime in.Best of luck.

I am not sure what temp the heads are at. I am going to figure it out though. Thanks for clarifying the tstats. I was figuring as long as they fully opened (which they do) It shouldn't overheat unless they were opening 50-60 degrees over specified temp.

 

[robaloroger]

Re: optimax tstats not opening quick enough

Have you checked compression to verify the integrity of the head gaskets?

Even a 10% difference in one cyl could indicate a small leak which will allow combustion gases to blow into the cooling system, displacing water, and cause an overheat.

Check compression carefully, write each reading down.

I checked compression when I bought the motor and it was from 88-100lbs. bottom port being the lowest. I will check again this weekend. Is there a way to check if the head gaskets should be replaced? I am pretty sure they are original because all of the head bolts look like a socket has never touched them.

 

[CharlieB]

Re: optimax tstats not opening quick enough

A cyl leak down test is the best method of determining the condition of the piston rings, however this required an air compressor and the leak down gauges, not too many guys have these readily available at home.

Looking at the DIFFERENCE in pressure between the cyl's is a fair indicator. They should all be quite near the same, within 5% or less.

100 is a low # and often cause for suspicion, however, the in-equality of gauges often can account for major differences on the same cyl. For this reason we pay more attention to the differences and not necessarily the actual #.

When a motor is so worn such that cyl pressure drops to 100 or less we begin to have serious lack of power and hard starting issues.

You do not have those problems so I would suspect your compression tester gauge is not very accurate, which is still OK to gauge the difference in each cyl.

 

[robaloroger]

Re: optimax tstats not opening quick enough

A cyl leak down test is the best method of determining the condition of the piston rings, however this required an air compressor and the leak down gauges, not too many guys have these readily available at home.

Looking at the DIFFERENCE in pressure between the cyl's is a fair indicator. They should all be quite near the same, within 5% or less.

100 is a low # and often cause for suspicion, however, the in-equality of gauges often can account for major differences on the same cyl. For this reason we pay more attention to the differences and not necessarily the actual #.

When a motor is so worn such that cyl pressure drops to 100 or less we begin to have serious lack of power and hard starting issues.

You do not have those problems so I would suspect your compression tester gauge is not very accurate, which is still OK to gauge the difference in each cyl.

This motor was a set of twins that I bought. Both motors have just about the same compression. 88-91-95-95-97-100. The numbers are spread pretty equally. It is not like 100-100-100-100-100-88. The motor has around 1000 hours so it has been used alot. The compression test was with the motor being cold. The gauge is pretty accurate because my other motors give me readings around 120 but that is on a carbbed motor. I know the v6 optimaxs are usually lower but 100 and above like you said. I know a 12% difference is not great but I was hoping I can run it for a while before it needs a rebuild. For the price of the twins (3k for both) I could not pass on it. I am going to check into what I need for a leak down test. I heard that is the most accurate way and I might as well have the right tools for it.
Thanks

 

[jeffersondodson561]

Re: optimax tstats not opening quick enough

I would check the poppet valve anyway, if you still suspect overheating. If it is slightly off it's seat, it will not build up pressure to allow tstats to properly work.