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Author Topic:   thermostat 225 mercury efi
brybasack posted 09-26-2005 01:08 PM ET (US)   Profile for brybasack   Send Email to brybasack  
how often on my mercury 225 efi do i change the thermostat..and where is
bsmotril posted 09-26-2005 01:38 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
It depends on the waters where you use your boat, and how religiously you flush the motors. You should certainly check them after 3-4 yrs of use. They are located under a housing at the top corners of each cylinder head. I have found that mineral rich water as found in limestone lakes and resevoirs does them in quicker than salwater. I've had a couple of mercs used in saltwater with T-stats that looked and worked fine after 1000 plus hours, and 8 plus years of use. The motors were flushed after every use with fresh water. BillS
Swellmonster posted 02-08-2006 10:57 PM ET (US)     Profile for Swellmonster  Send Email to Swellmonster     
I pulled and checked mine with temp guage on stove after 500 hours, no problem found, salt water always flushed
rtk posted 02-09-2006 12:04 PM ET (US)     Profile for rtk  Send Email to rtk     
If they are the same thermostats used for the Mercury 250 EFI, be prepared for some sticker shock with regard to the cost of the thermostat.

Mercury list price for the thermostat for the 250 EFI is over $50.00. Each.

I ordered thermostats and poppit valve parts to install as part of routine maintenance. On previous engines I have run in salt water I changed the thermostat(s) every two years or so. I just finished my second full season operating my 250 EFI in saltwater. It is a very easy process, and the parts are typically pretty cheap, so why not change them even if there is not a cooling problem.

I was a bit shocked with the total, and asked why. Of the $140 total, $108 of it was for two thermostats.

It's good to hear that the pricey thermostats do last a long time by what has been reported.

A change of thermostats will run you around $120 at Mercury list price, that excludes labor (2 thermostats and two gaskets). If price is a concern you may want to wait until there is a symptom of a cooling problem before changing them, given their reported reliability.

It is very easy to do, and the location at the top of the cylinder head is easily accessible. I changed mine while the boat was in the water and the engine was tilted up. Time spent was around a half of an hour on a nice evening while enjoying a few cold ones.


bsmotril posted 02-09-2006 02:03 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
I run Mercs in warm hyper saline bays on the TX gulf coast. I flush with freshwater after every use. I've had T-stats on 3 different V6 block motors (all 1991 or newer) go 7-8 years with no need to replace the T stats. I inspect them whenever I change water pumps 9100-150 hrs). I Only got 4 yrs out of the headgasket though on the '91 due to corrosion. I would expect a Poppit valve to go bad before a Tstat on a motor that is flushed regularly. BillS
sosmerc posted 02-10-2006 12:01 AM ET (US)     Profile for sosmerc  Send Email to sosmerc     
Most Mercs (and other outboards for that matter) are pretty good around salt water these days, but I still recommend you flush whenever possible. The best thing you could do is drop the boat in a lake and go for a spin every now and then....get the engine up to speed and temp so the thermostats and poppet valve will be opening and closing and really "flushing" things out.
rtk posted 02-10-2006 06:45 AM ET (US)     Profile for rtk  Send Email to rtk     
The ones I removed looked good. I flushed the engine (engine flushing attachment) after each trip, until the middle of last season. I dropped the quick connect for the flush in the water, so the balance of the season I did not flush. Just kept forgetting to pick one up.

On my previous engine, a Yamaha C90, the thermostat did not last until the end of my second season. When I put it on the muffs in the yard to winterize, the hot horn went off. The thermostats were pretty well shot, all rusted up and corroded. No flushing attachment on this motor, and the boat was slipped so it never was flushed during the season.


bsmotril posted 02-10-2006 09:13 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
I've found in general, motor designs with the T-stats at the top of the heads have less T-Stat corrosion problems than motors with the T-stats at the bottom of the block, or low, betweeen the heads. Probably due to all the water draining out after use versus pooling against the T-Stats.

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