Engine overheating

[gonesailing13]

Just took the boat out today . Got about two miles from the marina when the high temperature alarm went off. Shut the engine down to look for any obvious reasons but nothing. Shot temps off the engine and was definitely hot.The bottom was just cleaned so i know that’s not the problem. New fresh water pump on the engine, new impeller, all new coolant and oil. Was able to limp back to the marina but here i sit. Any ideas would greatly help. Not sure what’s going on. Also all new heat exchanger, oil cooler and transmission cooler.

 

[Mambo42]

How long was the boat stationary with the engines not running during the winter ?
It is possible you had some air in your cooling system and air cannot open the thermostat. I read you have exchanged the heat exhanger, which means you had to empty the coolant of the engine to a certain extent. If a bit of air was not bleeded out of the system than that could be the cause. If you want to prevent air locks you can drill a small hole in the thermostat, which will let the air through and ensure the thermostat will open.
It is also possible the thermostat got stuck, since it had been sitting for a while during the time you exchanged the heat exchanger.

I don't want to say that this was it, but I am just shooting ideas of what it could be.

 

[Bmarler]

Was the raw water side ok?
Did you get the proper amount of coolant in after the water pump change? Sometimes you can get an air lock and not get all the coolant back in.
If that’s ok, maybe stuck thermostat?

 

[High Wire]

Was there good water flow out the exhaust before leaving the dock?
Seacock open?
Bottom paint over through hull strainer?
Take the intake hose off the raw water pump intake and check for flow out of the hose.
Sea strainer clean? Lid closed air tight?
Any water leaks on that line? Water will leak out but also suck air in when the engine is running.
Intake water hose collapses when running?

Was the raw water pump impeller cover removed at all during the maintenance? If so then impeller inspected and new gasket? A small air leak on the suction side of the raw water pump can prevent pump function.

 

[Mainship Pilot]

Always try the easy first, close the seacock on the raw water strainer and check the strainer for stuff. As suggested, was the water flowing at start up at the dock out the exhaust? Is there coolant in the overflow? If these are good, then the odds are, impeller or stuck thermostat.

 

[O C Diver]

Along with what has been mentioned, with the engine cold, I would briefly run the engine to confirm raw water flow.

If no flow, from start to finish the issues could be:
Outside strainer if equipped is foul with growth.
Thru-hull could be plugged with growth.
Seacock could be closed
If equipped, sea strainer could be fouled.
Raw water pump could have broken blades.
Fuel cooler if equipped, could be foul.
After cooler if equipped, could be fouled.
Heat exchanger tubes could be fouled.
Transmission cooler could be fouled.
Exhaust mixing elbow could be fouled.

If you have raw water flow, you could have the following problems:
Thermostat(s) are bad
Belt driving the coolant pump is slipping or broke.
Coolant pump has an impeller problem.
Trapped air pocket in coolant system.

There may be other possibilities, but the above probably covers 98% of over heating problems.

Ted

 

[SteveK]

If all of the above checks out take a look at the new impeller.
I changed one and it came apart. was new in box in box when it went in.

 

[Mac G]

If you confirm you are pumping raw water and everything was working fine before you changed the coolant then I would suspect an air lock.
Did you persoanlly change the coolant or was it done by someone else?
Can you confirm the engine took back in the exact qualtity removed and required to bring her back up to the full mark?
Does she appear full when cold?
Is there fluid in the expansion tank?
Double-check that as an airlock can often be the cause.

 

[Altair38]

Another possible cause is that the raw water impeller was put back with the fins bent in the wrong direction. This happened to me as I was rushing to replace the impeller before the boat was launched the following day. I was using a hose to replenish water in the strainer. When I started the engine, water shot out of the strainer instead of being pumped thru the heat exchanger. It was a long night as I changed the impeller a second time.

 

[Bmarler]

Another possible cause is that the raw water impeller was put back with the fins bent in the wrong direction. This happened to me as I was rushing to replace the impeller before the boat was launched the following day. I was using a hose to replenish water in the strainer. When I started the engine, water shot out of the strainer instead of being pumped thru the heat exchanger. It was a long night as I changed the impeller a second time.

I have never heard of that happening. The fins will typically re-orient them selves as they rotate off the cam. Possibly something else going on?

 

[SoWhat]

Along with what has been mentioned, with the engine cold, I would briefly run the engine to confirm raw water flow.

If you have raw water flow, you could have the following problems:
Thermostat(s) are bad
Belt driving the coolant pump is slipping or broke.
Coolant pump has an impeller problem.
Trapped air pocket in coolant system.

and of course check coolant level.

 

[Shrew]

I have never heard of that happening. The fins will typically re-orient them selves as they rotate off the cam. Possibly something else going on?

Not always, I've seen this occur before as well. If they so easily re-oriented themselves, so many sets of instructions wouldn't take the time to advise to make note of the direction of the fins prior to removal and taking care to re-install in the same direction.

I have been able to take a split water pump with the new impellor and twist the shaft back and forth to flip the orientation of the fins, but that doesn't mean that it works in all water pumps.

 

[rslifkin]

The impeller fins will typically flip to the correct direction, but even if they don't, the pump can't pump backwards unless it's being spun backwards. The reason to insert the impeller with the fins already correct when possible is because having to flip to the other direction causes a bit of extra stress on the fins when it happens and on some impellers can lead to a slightly shorter life.

 

[tiltrider1]

Start with the easy diagnosis first. Is raw water coming out the back? Then move to is the fresh water circulating?

I suspect that the coolant was refilled too rapidly causing an air lock. This would show up as coolant not circulating. However, as previously mentioned there are many possibilities to this answer.

 

[gonesailing13]

After checking all the easy tasks I decided to check the thermostat. Not easy to get to on my engine probably the reason I didn’t check it first.took it out put in in some boiling water and surprise, didn’t open. Will be putting in a new one tomorrow and take her out for a try on the weekend. Pretty sure this was the problem. Thanks for all the ideas.

 

[Mambo42]

After checking all the easy tasks I decided to check the thermostat. Not easy to get to on my engine probably the reason I didn’t check it first.took it out put in in some boiling water and surprise, didn’t open. Will be putting in a new one tomorrow and take her out for a try on the weekend. Pretty sure this was the problem. Thanks for all the ideas.

Happy to hear you found the problem, now you can go out on the water without having to worry about that one anymore.

 

[rslifkin]

Stuck closed thermostats are a rare failure in my experience, but when they happen it's usually a moment of confusion. No apparent problems, everything seemed fine until suddenly it just kept getting warmer.

 

[BruceK]

After checking all the easy tasks I decided to check the thermostat. Not easy to get to on my engine probably the reason I didn’t check it first....

Ford Lehman? Tough to access,+ finger lacerations

 

[twistedtree]

Given the work that was done, I'll bet it's a closed intake valve. You won't be the first person to have that happen....

 

[ronobrien]

Check the mixing loop at the exhaust manifold. I have seen several get plugged with carbon and restrict the raw water flow out of the system, which also restricts it coming into the system