Boat thermostats

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So, replaced the impeller at the beginning of the season in the Supra, and it was in dire need, a couple of missing fins, some of the remnants of which were lodged in the inlet. I noticed water temp didn't get above 160 the entire season this year, whereas last year it ran at ~180, which I had assumed was normal.

Wrong.

Looked it up, the non-EFI PCM engines call for a 142F thermostat, the EFI ones call for a 160F stat, so it's bang-on and was actually running "hot" with the buggered up impeller, despite running cooler than a standard SEFI EEC-IV Ford, which it is. The cars had a 192F stat in them and a routine upgrade was to drop that down to a 180, which would still let it go into closed loop (wouldn't with a 160) but resulted in less timing being pulled.

So, I had mulled over the idea of putting in a 180F stat but figured I'd check the manual to confirm the 160 stock spec and I'm glad I did. This is from page 15 of the Service Manual:
Screen Shot 2020-10-04 at 8.46.07 PM.png


So it sounds like it is expecting ~160F. I found this surprising, as this is a departure from the cars.

Now, I recall a study years back when I was looking at the thermostat temp thing with the Mustang and I recall that wear increased when engine temperature was kept below 180F (another reason to avoid the 160 stats) and performance was reduced when you got above 190, hence the 180 being the "sweet spot", a perfect balance of low wear rates and performance.

This seems to go right out the window with marine applications where temps are generally significantly lower and even the EFI engines are run "cold" when compared to their passenger car siblings of the same family.

Anybody got some insight into the logic behind this?
 
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Just mulling this over, I think it may have to do with actual heating of the engine as opposed to the temp sensor location.
You would know better than I how these things work but are they not subjected to high RPM for sustained periods? The cylinder head and bore temps may be much higher than in a normal car engine and requires lower overall coolant temps to maintain the same temps in those areas as a 180 would in the car.

I really have no idea and may be blowing smoke out my backside, just thinking out loud,

Edited for spelling.
 
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So, replaced the impeller at the beginning of the season in the Supra, and it was in dire need, a couple of missing fins, some of the remnants of which were lodged in the inlet. I noticed water temp didn't get above 160 the entire season this year, whereas last year it ran at ~180, which I had assumed was normal.

Wrong.

Looked it up, the non-EFI PCM engines call for a 142F thermostat, the EFI ones call for a 160F stat, so it's bang-on and was actually running "hot" with the buggered up impeller, despite running cooler than a standard SEFI EEC-IV Ford, which it is. The cars had a 192F stat in them and a routine upgrade was to drop that down to a 180, which would still let it go into closed loop (wouldn't with a 160) but resulted in less timing being pulled.

So, I had mulled over the idea of putting in a 180F stat but figured I'd check the manual to confirm the 160 stock spec and I'm glad I did. This is from page 15 of the Service Manual:
View attachment 30906

So it sounds like it is expecting ~160F. I found this surprising, as this is a departure from the cars.

Now, I recall a study years back when I was looking at the thermostat temp thing with the Mustang and I recall that wear increased when engine temperature was kept below 180F (another reason to avoid the 160 stats) and performance was reduced when you got above 190, hence the 180 being the "sweet spot", a perfect balance of low wear rates and performance.

This seems to go right out the window with marine applications where temps are generally significantly lower and even the EFI engines are run "cold" when compared to their passenger car siblings of the same family.

Anybody got some insight into the logic behind this?

Yes jn a car you don't heat up the oil nearly as much the auto sweet spot takes into consideration you dont have super hot oil and infinite cold water.

A boat is under much more load than your car the oil gets and stays really hot burning off any moisture easily.
I can make the oil temp gauge shoot up to 250 before the water temp gauge moves at all.

In my small and big block I run no stats and its around 100 degree water sustaining about 400HP for hours on end running big lakes.
I do this in in my chevy marine engines that are lake water cooled it holds off detonation in 120-130 degree inlet temps in the high desert.

I run 165 in the ilmor 710 which is closed cooled with an exchanger.
 
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Trav is spot on. Marine engines are under constant heavy load and running at high rpm. You should also note marine engines are spec'd for 10w-40 oil to compensate for the load.
 

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Trav is spot on. Marine engines are under constant heavy load and running at high rpm. You should also note marine engines are spec'd for 10w-40 oil to compensate for the load.

Spec'd oil visc varies wildly depending on OEM and some have a chart relative to ambient. 20w-40 is a common grade but so is 10w-30. Some of the old ones we've owned spec'd everything from SAE 20 to SAE 50 relative to ambient.

This engine has some pretty "old school" oil specs:
Screen Shot 2020-10-05 at 8.26.01 AM.png


I've run 5w-40 (Delvac 1) these past two seasons but may run M1 0w-40 this coming one.
 

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Yes jn a car you don't heat up the oil nearly as much the auto sweet spot takes into consideration you dont have super hot oil and infinite cold water.

A boat is under much more load than your car the oil gets and stays really hot burning off any moisture easily.
I can make the oil temp gauge shoot up to 250 before the water temp gauge moves at all.

In my small and big block I run no stats and its around 100 degree water sustaining about 400HP for hours on end running big lakes.
I do this in in my chevy marine engines that are lake water cooled it holds off detonation in 120-130 degree inlet temps in the high desert.

I run 165 in the ilmor 710 which is closed cooled with an exchanger.

Interestingly, it seems "car temps" are normal for this engine family if it uses a heat exchanger instead of lake water cooling:
Screen Shot 2020-10-05 at 8.26.30 AM.png


Now, per the verbiage I posted from the service manual earlier in the thread, the ECM is going to be upset if I were to put in a 180, so I'm not going to, I'm going to leave the 160, but clearly there is accommodation in the design for what I would consider more "typical" temps if configured with a close circuit cooling system like in automotive applications so it can't just be head and wall temps then I wouldn't think, driving down the spec'd temp for once-through cooling?

Also, I find that carb'd applications spec'ing even cooler temps curious but I assume it has to do with the very low amount of airflow inside the engine cover, so heat soak of the carb is a reality.
 
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I've been away from the marine industry for 20 years so I'm a bit rusty.

Your right. The marinized engines were spec'd for 20w-40 and there was no deviation from this. Some Mercury's were 10w-40 probably for convenience and availability.

This was long before emissions on marinized engines. I'm sure much has changed in 20 years.

Diesels were always 15w-40 like over-the-road trucks.
 
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Back in my day fresh (raw) water cooled engines ran a 160 thermostat and closed systems ran a 180. Closed systems were easier to control. Raw water systems running in the Tropics (or in a nuke plant cooling lake) might start out with a much higher water temp. Also, closed systems were much more efficient.
 

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I've been away from the marine industry for 20 years so I'm a bit rusty.

Your right. The marinized engines were spec'd for 20w-40 and there was no deviation from this. Some Mercury's were 10w-40 probably for convenience and availability.

This was long before emissions on marinized engines. I'm sure much has changed in 20 years.

Diesels were always 15w-40 like over-the-road trucks.

This particular engine is an EEC-IV SEFI 5.8L (351W) Ford, probably very similar to the engine found in the 1st generation F-150 Lightning but marinized, so I assume has a different camshaft as one change to better match the marine operation profile. It's 310HP, which moves the little ~3,000lb Supra pretty well.
 
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All the marinized engines were hot rods with different cams. Ford, Chevy and Dodge. You probably remember eveyone latching onto a marine cam for the slant six. It's what I did!
 

irv

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So, replaced the impeller at the beginning of the season in the Supra, and it was in dire need, a couple of missing fins, some of the remnants of which were lodged in the inlet. I noticed water temp didn't get above 160 the entire season this year, whereas last year it ran at ~180, which I had assumed was normal.

OK, any idea how old or how long it had been since it was replaced prior? Mine is coming up on 5 yrs now and although I still have a strong stream, I am guessing it is time or getting close to having it replaced?
Prior years was always 3-4 yr intervals, (suggested by Merc) but since our boat isn't getting used like it use to with the young lad not coming up near as often, I am wondering if it can go longer? I have no water pressure gauge, unfortunately. (2007 Merc 90 H/P 4 stroke)
 

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OK, any idea how old or how long it had been since it was replaced prior? Mine is coming up on 5 yrs now and although I still have a strong stream, I am guessing it is time or getting close to having it replaced?
Prior years was always 3-4 yr intervals, (suggested by Merc) but since our boat isn't getting used like it use to with the young lad not coming up near as often, I am wondering if it can go longer? I have no water pressure gauge, unfortunately. (2007 Merc 90 H/P 4 stroke)

On the outboards I typically change it once the stream starts to get weak. On the inboards, it's once every few seasons as they are pretty cheap and easy to change.
 
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right from Boats.com and other sources:

Besides exposure to corrosive materials in the water, raw-water cooled engines suffered from another major drawback. They had a thermostat, just like all engines, but it was regulated at 145-150° F. This was done to minimize the possibility that salt in the salt water would separate out and crystallize inside the engine’s cooling passages, with 160°F being the critical turning point for this to occur. This comparatively cool running temperature limited the engine’s ability to reach a maximum level of thermal efficiency, which in turn had a negative impact on fuel economy and to some degree overall engine longevity. The cooler temperatures also caused varnish and gum buildup inside the engine, which ultimately contributed to other problems.

For fresh water, you can run a 180 degree thermostat. Here is the link: https://www.boats.com/how-to/inboard-engine-cooling-systems/
 

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right from Boats.com and other sources:

Besides exposure to corrosive materials in the water, raw-water cooled engines suffered from another major drawback. They had a thermostat, just like all engines, but it was regulated at 145-150° F. This was done to minimize the possibility that salt in the salt water would separate out and crystallize inside the engine’s cooling passages, with 160°F being the critical turning point for this to occur. This comparatively cool running temperature limited the engine’s ability to reach a maximum level of thermal efficiency, which in turn had a negative impact on fuel economy and to some degree overall engine longevity. The cooler temperatures also caused varnish and gum buildup inside the engine, which ultimately contributed to other problems.

For fresh water, you can run a 180 degree thermostat. Here is the link: https://www.boats.com/how-to/inboard-engine-cooling-systems/

Per the OP, that may be an issue with the programming in the ECM but the salt corrosion angle (definitely not an issue in this application) makes sense as to why the spec temp seems so illogical.
 
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Interesting and timely post. Out old Century (Merc MIE 260 5.7l)specs a 140dg thermostat, and typically reads just around that, rising slightly if we are using higher power settings for a few laps. I've considered going to 160 dg thermostat to get the engine running hotter as we typically do a lot of cruising just off idle. I need to do some more research and see if I can track oil temperatures.

I did see 180+ a while back after we sucked up some weeds into the strainer. Shot up fast and set the alarm off; I do a regular gauge scan but the alarm got my attention. Shut her down to stop the suction, waited a few minutes, started her up and and the elbows were cool ~30 secs later. Sure gets your attention.
 
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Interesting and timely post. Out old Century (Merc MIE 260 5.7l)specs a 140dg thermostat, and typically reads just around that, rising slightly if we are using higher power settings for a few laps. I've considered going to 160 dg thermostat to get the engine running hotter as we typically do a lot of cruising just off idle. I need to do some more research and see if I can track oil temperatures.

I did see 180+ a while back after we sucked up some weeds into the strainer. Shot up fast and set the alarm off; I do a regular gauge scan but the alarm got my attention. Shut her down to stop the suction, waited a few minutes, started her up and and the elbows were cool ~30 secs later. Sure gets your attention.
It's not an issue of oil temperatures. If it was, then why would a car motor run so much hotter and not see oil related issues. It's about the worry of salt crystallizing in the cooling passages.
 
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It's not an issue of oil temperatures. If it was, then why would a car motor run so much hotter and not see oil related issues. It's about the worry of salt crystallizing in the cooling passages.
my concern is the oil not getting hot enough to evaporate condensation. we are in freshwater so the crystallization issue isn't a concern.
 
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