MerCruiser Alpha 1 / 5.0 Carb Running Cool

[michael32211]

Hello,

New to the forum, old to boating & marine motors.

I purchased a used boat from a local boat dealer in July 2017.

Brief boat history, boat was purchased new in 2003 in central Florida (was a freshwater boat) by elderly owner who died 6-7 months after purchase. The boat sat in carport covered up for about 14 years. Boat was sold to a local marine dealer and serviced by highly regarded marine mechanic.

They did a pretty good job cleaning up the motor up and blowing it out. New carb, new fuel pump, 100 hr service. Since my purchase the boat has been ran 7-9 times for about 20-25 hours at varying speeds and conditions- zero issues surfaced.

However, every time I have ran the boat the temp Gage does not move a inch. only time any movement in temp gage is upon start-up. Moves uo to about 140 degrees and immediately drops as if the motor is off. The gage since my ownership has never move at all. Regardless of how the motor is ran the temp Gage does not move an inch.


So, I hired a mobile marine mechanic to look at it and fix. Took the boat out the next day ran for 4.24 hours at differing speeds and rpms. Most of the trip was a 2 hour 70% of WOT for 2.30 hours on plane- and still no temp change, needle sits flat on 100?

So I had the mechanic replace temp gage, temp sender, thermostat...and the motor still runs cool, so cool its cool to the touch.

Therefore my question is...has anyone experience this same issue?? All cylinders firing.

Just an fyi, I personally thought after putting 20 gallons of gas @$82.00 in it the motor burned a bit on the rich side when considering for amount of distance driven, time driven and conditions- smooth water (being on plane for almost the entire time at 3000 rpms @ 25 knts. in 67-70 degree water?)

Everyone I know is out of ideas, marine has not seen a boat run so cool in his 22 years, but states this motor runs cool, and the temp send is positioned in such a way that it does not get heated too easily.

any thought are appreciated.

Thanks Mike in North Florida

[Fiveslide]

Does it have a thermostat in​ it? Some people will take them out during winterizations so they can fill the engine with antifreeze.

[michael32211]

Originally Posted by Fiveslide

Does it have a thermostat in​ it? Some people will take them out during winterizations so they can fill the engine with antifreeze.

Hey Fiveslide

Yep, new thermostat, new temp sender and new new temp gage. Coolant was clear and without antifreeze. Thank

[Sailmonkey]

Where is it cool to the touch?

Have you shot it with an IR heat gun?

[michael32211]

Hey

It’s cool to touch on entire cooling system- hoses, thermos area and water exchange on each side of the motor. Sorry I don’t know the name of those two square looking things.

Marine touch as I did...nothing..luck warm.

I hope this helps..

Thank you for asking

[Sailmonkey]

Sounds to me like the thermostat is stuck open.

[michael32211]

It’s been replace with new....no change in gage...

[LLizzard]

Originally Posted by michael32211

It’s been replace with new....no change in gage...

If the sender and gauge have been replaced and are working, this has to be a thermostat issue IMO.
1) Can you test the sender and gauge by removing the sender and putting it in a cup of hot hot water while keeping it connected to the gauge and grounding it like it is inside the engine? see if the gauge moves.

2) Given its cool to the touch, I'm guessing you got a bad new thermostat. I've had brand new thermostats fail to open or close. You can test by removing it and alternating putting in hot and cooler water and see if it opens and closes. A thermostat that is closed will force an engine under load to heat up pretty quickly. Now I test all new thermostats on the stove before doing the work to install it. Do you know the heat rating, where it opens, of the thermo? It's usually stamped on it. Are you seawater or coolant cooled? If seawater, running that cool may clog seawater cooling passages over time. Seawater cooled engines need to run at least 140*

Your fuel burn does not seem exorbitant. However running an engine that cool will effect efficiency and could shorten engine life long term.

I am not a mechanic but have done a lot of cooling system work on my boats thru the years.

[flyingfin]

I intentionally removed thermostat on an older Merc 351 5.8L 233hp I.O
It always ran cold around 160 degree. Make sure you only run it on ethanol free fuel and you wont have any problems as long as you are in southern waters, colder water may cause you issues. Dont forget you are running it at over 3,000 rpm. If that engine was in your car, that would be 75 to 90 mph constantly!

[michael32211]

You are so right, i’m Not hard in my motors...doing so to much risk when crushing near off shore.

Yes, I run ONLY marine Valtech 89 oct. for fuel. We replaced the them with a new QuickSilver 160* theme and the gage is flat line. I have begun to adopt that the new thermostats maybe bad...because there is no way it can run this cool.

As I mentioned I have owned some boats in my time, even had one catch on fire in the water...thanks to improper maintenance, thus now I doing give a **** what it cost...I want it right. Hence the focus on what seems to be the opposite running cool.

Thanks for your thought..

[jimbunyard]

What you describe is normal for a raw water cooled Mercruiser.

After warm up, the exhaust manifolds should be very warm to hot.

The temperature sender is located right in the t'stat housing/water distribution manifold, which receives seawater directly from the pump mounted in the outdrive and even though the sender is located on the 'hot' water side of the manifold, when the t'stat opens, the temp can drop pretty quickly, which explains your initial spike to 140 and then drop to (probably) 100 or so.

That the temp goes to 140 and then drops would seem to indicate that the electrical side of the temp monitoring system works correctly.

A failed thermostat would not open, which would cause the engine to overheat.

If the thermostat somehow failed in the open position, that can be easily be visually verified upon removal, but again, the temperature spike to 140 seems to indicate that the system is working as designed...

As previously suggested, an infrared heat gun used to take the temperature of the engine at various points (on the exhaust manifold where the exhaust exits the head, where the riser hose is clamped to the riser, the oil pan after a hard run) is invaluable in finding overheating problems.

The relatively cool water this time of year also exacerbates the 'problem'... but it is much better for a raw-water cooled engine to run cool than hot.

[michael32211]

Hey Jim!

Thanks for your insights, at the end of the day...I have to assume it’s one of the other. A) bad thermostat or B) it’s normal operation, trying to find a problem where their is none.

I so appreciate the intelligent way you answered, clearly you and LLIzard have some experience with kind of kinda thing.

I knida think it’s on the normal side because regardless of water temp and after replacing everything the temp is the same...ran at this temp when in summer or winter water. Wheather idealing for 30 mins or for full bore for 20 minsters. So I think it’s just the way the motor runs. Which is good, now I focus on the other pain my ass the fumble barring.

Merry Christmas.

[jimbunyard]

Gimbal bearing isn't too hard (unless the outdrive is stuck, but with low hours on a freshwater boat this isn't likely).

6 nuts to remove the outdrive, four to remove the tilt rams, reach in and twist the bearing in the aluminum tolerance ring 90 degrees to align with the notches (you might have to tap it with a rod or screwdriver and hammer in the appropriate place to get it started), pull it out by hand. Take the new bearing out of the new tolerance ring with the same method, and install it with the reverse procedure into the existing tolerance ring in the gimbal housing. Make sure the grease hole in the brg lines up with the grease channel in the tolerance ring when you install it.

Borrow or buy (about 25.00) an engine alignment tool to check your engine alignment before you reinstall the out drive; this is important.