Suzuki DF140 thermostat help

[freespirit3]

After some Suzuki advice
I have a Redbay 6.1 with a 2003 Suzuki DF 140 outboard, it has 550 engine hours, recently we stripped the engine as it had a small oil leak from corrosion, whilst apart cleaned out any salt deposits and blanked off the metal plug in the exhaust that corrodes quite badly.
Rebuilt with new gaskets and it runs sweet, have used it all weekend on the sea (in the sun) and noticed that the engine temperature is only around 40 Deg C (even after 30mins running) , it also de-rated the power a couple of times which maybe a coincidence?
I think the thermostat maybe stuck open but open to ideas, plus it maybe that the thermostat is the original and hence tired. good flow of water and the tell tale is ok.
Question is I see that there are two thermostat temp versions 60 Deg C or 71 Deg C, what would you guys go with based on the fact that I am using it in the UK and what would the benefits be?
Thanks for reading

[Limecc]

Precious little information on the hotter stat but there is some helpful info here:
https://www.suzukioutboardforum.com/...-for-my-engine

I've just fitted the hotter stat reasoning that it will keep the oil in better shape and the average water temperature here in the UK is lower than that in more tropical latitudes. It runs well but it always has anyway, can't say I've noticed a difference.

I got it from PA Lynch for £38, the part number was different from what I found on the Brownspoint online parts catalogue so better check with them first if you decide to order.

[freespirit3]

Originally Posted by Limecc

Precious little information on the hotter stat but there is some helpful info here:
https://www.suzukioutboardforum.com/...-for-my-engine

I've just fitted the hotter stat reasoning that it will keep the oil in better shape and the average water temperature here in the UK is lower than that in more tropical latitudes. It runs well but it always has anyway, can't say I've noticed a difference.

I got it from PA Lynch for £38, the part number was different from what I found on the Brownspoint online parts catalogue so better check with them first if you decide to order.

Many thanks for this

I have ordered the hotter stat as I fully agree that the engine should run abit warmer especially as our UK waters never get above 15 Deg C, this weekend we saw 12-13 Deg C in wales in full sun.

[charliee]

full sun in Wales - are you sure? Yes just change the thermostat and cross fingers.

[Pikey Dave]

Surely the temperature of the sea is irrelevant. The whole point of having a thermostat is to maintain a constant temperature regardless of the sea temperature. A 60deg stat will maintain an engine temp of 60 deg, and a 71deg likewise.

[Striker]

If it’s any help my DF140 runs around 75-78 degrees on the clock so presumably fitted with the higher thermostat.

Agreed sea temp was 13.8 degrees off Anglesey this weekend but that shouldn’t affect the engine temp as the thermostat is governed by the temperature of water in the block rather than ambient.

By car standards 75-78 is cold and given that it’s basically a 2.0 vitara block I wouldn’t want to run it much colder as I was always taught that cold engines wear quicker.

[scrambler]

I'm interested in this discussion of Df140 running temps as there is something I'm curious about which I'm hoping someone can explain.
I have an RC585/DF140 both new in 2018, now done about 250 hours. Quite early on I had an overheat alarm whilst at displacement speed around 5.5 knots on my regular river run (up and down the Hamble). Couldn't find the cause of the overheat so maybe picked up a bag or something but it has made me a bit obsessed with watching the engine temperature.
When cruising at 20-30 knots temp is consistently around 133/135 Fahrenheit (56/57 Celsius). However at 5.5 knots on the river it will slowly climb to about 143° or higher. When I reach open water and start to plane it will immediately drop to the lower range 133/135.
At displacement speed I've been accustomed to keeping the trim at 0% but one day recently I accidentally left the trim at 35% and didn't notice it for a while. When I did I also noticed that the engine temp was 131°.
So by trimming up I can now keep my engine temp in the low 130's but reading the comments in this thread about it being better to run hotter I'm beginning to wonder if I'm doing the right thing?

[Limecc]

After doing a little research I found out a few things to share.

Car engines typically have a thermostat set between 82 and 92°c. The hotter the engine the more efficient it will be. This is on the basis that the fuel/air mixture burns at a certain temperature and some combustion heat is lost to the cylinder which in turn is transferred to the cooling water.

82°c (180°f) water temperature is required for cylinders to achieve a minimum specific temperature in order to allow a fully homogenized air/fuel mixture to combust efficiently.

When oil is below the boiling point of water, moisture is building up in the crankcase. In the combustion process every time there’s a cycle, water vapor is produced. You then have blow-by, which all engines are victims of to some degree, and there's going to be some level of moisture build-up and this will get worse over time until the oil is changed.

The commonly used 71°c (160°f) thermostat is way too low to be considered for performance or engine longevity. Engine wear is increased by double at 71°, than at 85°c (185°f). So then, why do the 71's exist in the first place? The 71's were commonly used in older, open loop cooling systems where only 6 pound radiator caps were used, and low 100 degree boiling points were experienced.

In the marine environment with the older 60° stat, engine wear and oil degradation will be even worse. This must be why Suzuki introduced the 71°c thermostat. This is still 10° lower than the ideal, but obviously the maximum - given that outboards don't run a pressurized cooling system.

The ideal oil temperature is between 100°c and 118°c (212-245°f). It has to be hot enough to boil off moisture and other contaminants, but not too hot that additives are harmed and the oil starts breaking down (137°c/280°f max temp).

Regarding the best oil grade, the statement below is from Suzuki (I took the liberty of converting °f to °c for clarity):

We suggest that customers use genuine Suzuki 4 Cycle Engine Oil. We feel our oil is the best available on the market today. Our oils are formulated to provide superior lubrication and protection for internal engine parts in the harsh marine environment. Suzuki oil meets the National Marine Manufacturer Association (NMMA) Four Cycle Water Cooled (FC-W) standards. The actual oil recommendation is: SAE or NMMA FC-W 10W-40 (operating in temps from -10°c/14°f to over 37°c/100°f), or 10W-30 (operating in temps from -20°c/4°f to 30°c/86°f) API or NMMA FC-W Classification SE,SF,SG,SJ. For temps below -26°c/15°f use SAE or NMMA FC-W 5W-30.