1993 OMC 48SPL Engine Thermostat Service Life

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Oldslowandugly
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1993 OMC 48SPL Engine Thermostat Service Life

Postby Oldslowandugly » Sat Oct 05, 2019 10:35 am

Once again the thermostat in my 1993 OMC 48SPL engine has stuck in the open position. It was installed in the Spring and only lasted five months. When I get home I submerge [the engine thermostat[ in vinegar. The vinegar turns green from the dissolved corrosion on the brass pellet mechanism. After a while in the vinegar [the OMC engine thermostat] seems to work okay again, but these treated thermostats never work perfectly.

I don't get [the short service life]. I know [an outboard engine cooling system thermostat] leads a tough life in saltwater but my engine used to run years on the same thermostat with no problems. I only buy real OMC parts, yet they are failing regularly.

jimh
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Re: 1993 OMC 48SPL Engine Thermostat Service Life

Postby jimh » Sat Oct 05, 2019 10:51 am

Perhaps in the 26-years since your 1993 OMC outboard was originally manufactured, the thermostat part supplier to OMC changed. Perhaps the parts you buy now, 26-years later, are not the same quality as the part supplied by the manufacturer in 1993. Or, perhaps you are buying parts that have been sitting on a shelf for 26-years, and those parts have decayed during those 26-years of non-use.

I infer your use of the engine is in saltwater. Are your thoroughly rinsing the cooling system of the engine in freshwater following each use? Do you allow the engine temperature to rise to the point where the thermostat will open and be flushed with freshwater?

Oldslowandugly
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Re: 1993 OMC 48SPL Engine Thermostat Service Life

Postby Oldslowandugly » Sat Oct 05, 2019 4:58 pm

JIm, any and all of the above could be true. Perhaps they just don't make them like they used to.

biggiefl
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Re: 1993 OMC 48SPL Engine Thermostat Service Life

Postby biggiefl » Mon Oct 07, 2019 11:10 am

Why are you bothering? Drill out the thermostat and put the "plug" that is left back in and run. It will have sufficient backpressure and will not run too cold. Unless running in cold temperatures a LOT, it is not really necessary to run a thermos if it is giving you grief.

PS: they make aftermarket SS thermostats which won't corrode like OEM brass does.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall. :roll:

Oldslowandugly
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Re: 1993 OMC 48SPL Engine Thermostat Service Life

Postby Oldslowandugly » Mon Oct 07, 2019 11:02 pm

I used to own some ancient Evinrude 30-HP engines. They had no thermostats and ran poorly. I really welcomed the idea of decent operating temperature. The carburetors work better with [an engine whose operating temperature is regulated by] a thermostat.

I don't even like the way [ancient Evinrude 30-HP engines] run when the [thermostat] is stuck open, let alone drilling it open for good.

Q: Where do you get stainless steel thermostats?

biggiefl
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Re: 1993 OMC 48SPL Engine Thermostat Service Life

Postby biggiefl » Tue Oct 08, 2019 11:16 am

Removing them makes them run cold. Removing the guts and replacing the "plug" is the same as it being open. Check online. I used to get mine I think from Sierra.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall. :roll:

Oldslowandugly
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Re: 1993 OMC 48SPL Engine Thermostat Service Life

Postby Oldslowandugly » Sun Nov 03, 2019 9:42 am

I can not find a stainless thermostat for this [1993 OMC 48SPL engine]. And the brand new one is acting up already after only a month of usage. Since I have a few bad ones on hand maybe I will experiment with drilling holes in them. A hole of a specific size should result in a specific operating temperature and still unseat at WOT. They fail in the open position, so I guess if I epoxy the thermostat shut, then drill a hole, it will act like a restrictor similar to what they use in racing car engines.

dtmackey
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Re: 1993 OMC 48SPL Engine Thermostat Service Life

Postby dtmackey » Sun Nov 03, 2019 9:39 pm


Oldslowandugly
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Location: Queens NY

Re: 1993 OMC 48SPL Engine Thermostat Service Life

Postby Oldslowandugly » Mon Nov 04, 2019 10:02 am

Nice site. Mine is not listed.

Oldslowandugly
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Re: 1993 OMC 48SPL Engine Thermostat Service Life

Postby Oldslowandugly » Tue Nov 05, 2019 7:08 pm

Well I pulled the boat out for the winter. I have the motor hanging in a big barrel so I can do a flush and tune. I usually wash the boat at this time and I toss some boat soap in the barrel to clean any salt out of the motor. Not only did the balky thermostat work fine again, all of the other ones worked fine too. I had three bad thermostat sitting in vinegar for weeks to clean them. All four worked fine but one ran a bit hot. These all had originally stuck open and ran cold. So it looks like they are getting stuck from sea salt and vinegar cleans them. Perhaps I need to rig some sort of fresh water flush like the big motors use.

dtmackey
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Re: 1993 OMC 48SPL Engine Thermostat Service Life

Postby dtmackey » Tue Nov 05, 2019 9:40 pm

Sorry about that, I looked and it showed a HP range and the 48 fell in that line, but after I dug into the Evinrude specific parts diagram and backed out the specific PN# for your motor, it seems to be a very narrow series of models it fits.

I'm surprised you are having problems. I've run brass [thermostats], but materials, conditions, and a host of other factors come into play.

D-

Oldslowandugly
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Re: 1993 OMC 48SPL Engine Thermostat Service Life

Postby Oldslowandugly » Wed Nov 06, 2019 9:36 am

Yes, I agree. My 30-35 hp motors use the old style small stainless/brass thermostat that rarely fails. In fact the only time I had a problem was when a tiny little snail shell got lodged in the mechanism and it stuck open. Good thing too because on those models the entire thermostat cover must come off the head and a new gasket used. This 48hp has the neat screw-on thermostat cover that comes off with a spark plug wrench. But it also fails regularly. The fact that vinegar loosens them up tells me that is salt is the culprit. Perhaps when the motor stops running and drains, the stat is left high,dry, and hot causing salt crust to form. Flushing after use may be the solution but where to hook up a flushing hose barb? Probably the thermostat housing itself could be drilled and tapped for a barb fitting. Then run a hose out the lower engine cover with a quick connect. Something to consider over the winter.