Cat 3116 overheating. Can't figure it out.

[wickedwheels]

I've got a starboard engine that overheats on a '99 370 at over 2000 rpm. Seems fine on idle.

I dove under and couldn't find anything clogging the intake. Sea strainers are clear.
I replaced the impeller, which seemed fine.
Today I replaced the thermostat and checked the heat exchange. Heat exchange seemed clean. Old thermostat moved when boiled. I'll post pictures.

Just as a side note... last year I overheated after kissing a sandbar and then had engine issues. The marina replaced the injectors, but I'm totally convinced that they misdiagnosed my issue as it kept happening until I had the fuel tank cleaned out and rebuilt Racors a few times. I think bad gas caused engine issues and the marina went for the injectors because I overheated. Either way, this is the same engine.

 

[Thornton69]

The exchanger looks anything but clean in your photo. You likely have raw water circulation problems

 

[NotHerDecision]

Have you checked the temp manually? Just making sure it’s not a gauge or sending into failure. Also potentially the coolant pump or raw water pump itself. And have you checked everything in the cooling circuit ie transmission coolers, fuel coolers…etc.

 

[dtfeld]

First of all define overheats...what temp does your dash gauge indicate, and does the system monitor indicate an over heat as well? Just trying to eliminate faulty gauge. Do you have a IR thermometer to confirm the temps?

What about transmission and fuel coolers? They are inline downstream from the HEX , and could be a potential bottleneck. Transmission cooler is smaller and smaller tubes as I recall.

Also, check the belt on the coolant pump, and confirm coolant pump turning.

 

[wickedwheels]

Have you checked the temp manually? Just making sure it’s not a gauge or sending into failure. Also potentially the coolant pump or raw water pump itself. And have you checked everything in the cooling circuit ie transmission coolers, fuel coolers…etc.

I checked the temp with a heat gun. It's overheating.

Also, water is shooting out the back normally, so I assumed it's not the pump

 

[fwebster]

The heat exchanger is clean enough to cool the engine if there is adequate water flow. Remove the end cap on the heat exchanger on the inlet side and see fi you see hunks of impeller clogging up the area before the tube bundle. Next, pull the basket out of the strainer and stick a shop-vac hose down in the strainer and try to vacuum out anything that isn't water.........if you grounded the boat and tried to power off the sand bar you could have sucked up a bunch of sand and debris which will clog up the strainer and impede the water flow.

This shouldn't be hard to figure out. Cat 3116's have a lot of excess cooling capacity and one of the causes listed above usually fixes an overheat problem.

 

[dtfeld]

I checked the temp with a heat gun. It's overheating.

Also, water is shooting out the back normally, so I assumed it's not the pump

Coolant pump/belt?

 

[wickedwheels]

The heat exchanger is clean enough to cool the engine if there is adequate water flow. Remove the end cap on the heat exchanger on the inlet side and see fi you see hunks of impeller clogging up the area before the tube bundle. Next, pull the basket out of the strainer and stick a shop-vac hose down in the strainer and try to vacuum out anything that isn't water.........if you grounded the boat and tried to power off the sand bar you could have sucked up a bunch of sand and debris which will clog up the strainer and impede the water flow.

This shouldn't be hard to figure out. Cat 3116's have a lot of excess cooling capacity and one of the causes listed above usually fixes an overheat problem.

The sandbar was last year. Everything has been vacuumed and it ran fine after the fuel issue was sorted out. Sea strainers are fine. Nothing in the heat exchanger.

I considered belts, but if water is shooting out okay doesn't that mean that the pump is all good?

 

[dtfeld]

The sandbar was last year. Everything has been vacuumed and it ran fine after the fuel issue was sorted out. Sea strainers are fine. Nothing in the heat exchanger.

I considered belts, but if water is shooting out okay doesn't that mean that the pump is all good?

Raw water pump is gear driven. Coolant pump is belt driven.

 

[The Bill Collector]

Transmission heat exchanger can definitely impact water flow.... Check it out.

 

[Thornton69]

The pic of the exchanger is taken from a bad angle. It appears that at least 5 of the tubes are restricted. Bet there is quite a few more. Not sure how anyone can rule it out as a problem without going deeper? If 30% of the tubes are blocked, you will lose close to 30% of it's cooling capabilities. Increasing the flow in the unrestricted tubes is likely not going to give much of that back.

 

[dtfeld]

If you have what you consider normal waterflow from the exhaust, I would concentrate on the coolant side.

That's not to say the HEX or other cooler doesn't have blockage. When I cleaned mine last time, I found impeller fins extruded way down into the tube and these had to be rodded out. But that HEX on first look seems ok...but might warrant a closer look down the tubes if no other solution is obvious.

In addition to a bad pump/belt, have you checked or replaced the coolant lately? Reason I ask, is if not, you may be getting rust/debris in the system. My understanding is the thermostat housing has a small orifice that allows hot coolant to get to the thermostat allowing it to open sooner...so maybe clogged.


***Edit: the coolant bypass may only apply to the 3126...

 

[dtfeld]

Here’s the CAT list of things to troubleshoot...some things need to be adjusted for the marine engine... i.e. cooling fins =HEX, or converter from CAT speak. Water pump refers to the coolant pump, Sea Water or auxiliary pump is the raw water pump etc.

 

[dtfeld]

 

[wickedwheels]

So it was the belt for the coolant pump. Found the broken one...

Here's the kicker... I had belts on the boat (from the previous owner) and tried to install them. I removed a cover (from the alternator?), removed the flywheel from the engine, took off the belt for the alternator(?) by pivoting it out of the way. I loosened up the tensioner pulley to get the belt on the pump, but it won't go on. It's so tight that it won't connect between the engine and the pump, even if I bypass the tensioner pulley. The part numbers are the same between the old belt and the new. Ugh!!!

 

[dtfeld]

The good news is these CAT engines are pretty tough, and it usually turns out to be something pretty simple!

Easy DIY fix and back to boating !!

 

[wickedwheels]

The good news is these CAT engines are pretty tough, and it usually turns out to be something pretty simple!

Easy DIY fix and back to boating !!

Well, not so easy. I can't get the belt on

 

[dtfeld]

Measure the belts...I wouldn't assume the PO had the right belts, or put them in the wrong package, mislabeled them etc.

I have the measurements somewhere...but it'll be tomorrow.

 

[Strypes]

You could always hire a professional.

 

[kvduff]

You could always hire a professional.

God forbid a guy wants to fix his own boat. Kind of a dickish thing to post to forum dedicated to members helping members.