Switching to a 180*F Thermostat

[garycinn]

All this talk about thermostats has me ask a question about my engine -- a '01 Merc 4.3L TBI raw water cooled.<br /><br />I was talking to my Merc tech asking if he could alter the fuel map in the computer to run leaner so I wouldn't get fuel dilution in the oil. He said no, he couldn't modify it.<br /><br />I'm concerned because my last oil change had very high fuel dilution (close to 7%).<br /><br />He said that the cold water (I run early and late in the season) in the fresh water cooling system can cause the computer to dump in more fuel.<br /><br />Since I have a 160* stat in right now (probably the original), what if I changed to a 180* stat to run a little warmer? Or is this too hot a stat on a fresh water cooled engine. My reasoning would be to run warmer to be more efficient, leaner, and reduce fuel dilution of the oil.<br /><br />I am also toying with the idea of adding closed cooling to it, but don't like the relatively high cost. I understand that you change the stat when doing the conversion to a 180*.<br /><br />BTW, I don't and don't have plans to run in salt.<br /><br />Also, if the 180* is too high for FWC, what about a drilled 180* stat to get me in between 160 and 180?<br /><br />Also, my VDO dash gauge keeps the temp constant at about 160* once the engine is warmed up. It never moves no matter how I am running it.<br /><br />I have a IR temp sensor, but will have to wait until next spring to run as I winterize over Thanksgiving .<br /><br />Thanks

 

[garycinn]

Re: Switching to a 180*F Thermostat

Ron,<br /><br />Thanks for the helpful post. Yes, I have an electric fuel pump. I have 175 hours on the engine currently -- 145 when the high dilution sample was taken.<br /><br />Here is my last UOA:<br /><br /> http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=3;t=001855 <br /><br />It was Merc 25W40 dino. I captured the sample for the last third of the season (30 hours) and will be sending it in soon.<br /><br />Just winterized boat with new Merc 25W40 syn blend.<br /><br />I think when I took this last sample, I had just run it at the lake. 60 minutes later at the house caught the sample w/o running on muffs. Caught it mid drain.

 

[ron7000]

Re: Switching to a 180*F Thermostat

I have an '02 Bayliner with the 3.0L,<br />last years OA showed 4% dilution, this years 2% for 40 hrs on the oil,<br /> http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=3;t=002095 <br /><br />can you post your OA? or is it over at bitog?<br /><br />I 180 stat shouldn't hurt if your in fresh water or primarily run frequently through fresh water to flush it out. I've run a 180 in my carb'd 351w with no problems.<br /><br />Its fuel injected, so there's no mechanical fuel pump running off the cam which would be seeping fuel into the crankcase, correct? I'm wondering that about my 3.0. Except for that, I can't foresee any other source of the dilution other than blowby past the rings, and I'm sure you have good rings. If anything, the motor might still be breaking in. How many hours on the motor? I have 80 on mine.<br /><br />I would agree the hotter the motor, and oil temp given sufficient running time, the better you should be able to control fuel dilution. My 3.0L runs 175 on the dash gauge. But if it's constantly running rich due to the ECU's fuel map, then I don't see the thermostat affecting it much. But I would certainly try a 180 stat given it's cheap and easy to do.<br />What you might also try looking into before FWC is fooling the computer with something maybe as easy as a radioshack resistor, into thinking the motor is always at operating temp or it's hot when cold so that it doesn't run richer. An inexpensive mechanical oil temp gauge would also give you some insight.<br /><br />On my last uoa, blackstone mentioned a good point about taking the sample. They've noticed higher fuel #'s when taking it after starting a cold motor and warming it up vs. taking the sample cold. Is it possible when you took the sample, a cold start and lack of run time at operating temp may have skewed your fuel #? But I would still worry about 7% dilution, as long as it wasn't a lab mistake and the viscosity # correlates with the dilution.<br /><br />What oil you run?

 

[Boomyal]

Re: Switching to a 180*F Thermostat

Gary, go with the 180 if you're primarily in freshwater. It is better all the way around. It will probably help your fuel dilution, especially if your injection does not use an oxygen sensor to control A/F mixture. I would assume that your ECU is marine specific and it should compensate for running at cooler temperatures. But it can only go so lean when your always running cold. The ECU's are definitely temerature sensitive. You can always experiment. Go hotter for X number of hours then resample the oil. I'll bet your engine will even run better at 180.

 

[garycinn]

Re: Switching to a 180*F Thermostat

Thanks, Boomyal.<br /><br />I do have an oxygen sensor on the flame arrestor. I think I will try the 180*. I have fogged the engine for the year and drained it, but haven't opened up the stat housing to pour in the Prestone low-tox / distilled water mix. I'll make the swap now and see how the first ~30 hours go next year. I'll also report back in a couple of weeks when I get my other UOA report back to see how the dilution turns out for this second oil change.