Simulating full load dock side 2GM20F

[mz4wheeler]

I'm experiencing an overheating issue that seems to crop up when I'm running at 3000 RPM for about 10 minutes. The alarm sounds, I reduce RPMs to 1000 RPM, alarm goes away. If I run the engine at 2500, no alarm.

Typical, so I'm going to start troubleshoot the whole cooling system.

However, the question I'd like to ask is what is the best way of simulating a large load TIED to the dock? I'm thinking that I'd just put it into gear, rev up the RPMs to ????.

That is the question. Being tied to a dock WILL load the engine, but obviously I wouldn't go to 3000 RPM. Has anybody had success loading an engine dock side with a 2GM20F, if so, what RPM is recommended? 1000? 1500? 2000? What is "safe" for the engine, transmission, prop?

Thanks!

 

[Calif. Ted]

What is "safe" for the engine, transmission, prop?

Usually more a case of what is safe for the dock and cleats you are tied to and many marinas prohibit the practice in their lease agreements. Wouldn't you need to run at 3000 to reproduce the overheat condition anyway ? How old is your raw water impellor, usually an easy place to start.

 

[Ralph Johnstone]

All sorts of easy things to check eg. raw water impellor, total raw water flow, mixing elbow, strainers, heat exchanger, temp. sensor, thermostat, as Calif. Ted has mentioned. These are all done with the engine off. Start with the easiest (cheapest) things first and work your way up.

You know it's overheating so recreating it at dock side isn't going to accomplish anything.

 

[Bill Roosa]

Well you can rule out the thermostat and low anti levels. If the problem goes away when you reduce power you have a heat transfer problem. That means not enough raw or anty flow so check the raw water impeller and engine drive belt (water pump slipping?)
or
the heat exchanger is fouled
or
the raw water intake, strainer, hoses.... are restricting the flow
or
the port in the mixing elbow is restricting flow
or
you have a bad temp sensor.

 

[Bill Roosa]

I stand corrected the thermostat may not be opening all the way which would also restrict the anti flow so you will want to check that also.

 

[mz4wheeler]

All sorts of easy things to check eg. raw water impellor, total raw water flow, mixing elbow, strainers, heat exchanger, temp. sensor, thermostat, as Calif. Ted has mentioned. These are all done with the engine off. Start with the easiest (cheapest) things first and work your way up.

Well, when this issue cropped up a couple of weeks ago, I found a VERY lose seawater pump belt, and I thought that was it. Before I discovered the belt issue, I already checked and cleaned the seawater strainer. I ordered a new thermostat so I'll put that in tomorrow, along with replacing the impeller. THEN I wanted to test it w/o leaving the dock.

I do have a thermo laser and when I checked it last night the block was about 210 degrees. So, I'm hoping for an easy fix.

I do have quite a bit of water spitting out the exhaust (kinda eliminating the impeller), so the only theory that sticks is a stuck thermostat. However, I'm predicting a cleaning of the heat exchanger in my future.

 

[Stu Jackson]

mz4,

Wait!


Please.


Only do ONE THING AT A TIME.

It is the ONLY way to know what the issue was.

If you do all those things at once and then take it out and it works, what will you have learned? That it still could be any one of ten things?

Think it over.

Good luck.

PS - "Engines for Dummies" is my favorite book!!!

PPS - Usually the HX, wouldn't hurt to change the thermostat once every ten years or so.

 

[Johnb]

When I was buying my boat the engine surveyor tested it by running at max RPM tied to his dock for 30 minutes. You might make a lot of enemies if you do this in your marina, it is amazing how much water gets circulating.

At the risk of being a little contrary, if you know the raw water system has not been overhauled in a long time you might as well do it all in one fell swoop. On my particular engine I replaced the fresh water hoses as well because some were easier to get to while the heat exchanger was out of the way and some of course connected to the heat exchanger.

 

[Ralph Johnstone]

THEN I wanted to test it w/o leaving the dock.

Any chance of taking it out with someone else at the controls while you're down below checking the engine under load ? No worries about ripping the dock out.

While you're down there, place your hand on the mixing elbow to get an idea of the water going through the exhaust. It should be little better than lukewarm on the outside radius. One of these little buggers can cause overheating problems not to mention loss of power.

 

[mz4wheeler]

When I was buying my boat the engine surveyor tested it by running at max RPM tied to his dock for 30 minutes.

At the risk of being a little contrary, if you know the raw water system has not been overhauled in a long time you might as well do it all in one fell swoop.

Wow... I would think this could damage the cutlass bearing (my worry). However, it would certainly test the drive train under extreme stress. I bought this boat two years ago, and I figured I'd just overhaul the whole cooling system (now that I actually have a problem).

However, I have really terrible access to the left side of my engine (photo), which is where all these major cooling items are located. Not looking forward to that.

 

[mz4wheeler]

While you're down there, place your hand on the mixing elbow to get an idea of the water going through the exhaust.

I saw that scary photo of that cut-away mixing elbow before [grin], and since my boat is an '89, maybe mine also looks like that.

I think I need to install a real temperature gauge.

 

[Jeff]

I had a similar problem a few years ago. I had a bad gasket on my strainer basket. At high RPM's it would suck in air and circulate less water. I made a new cork gasket and the problem went away.

 

[mz4wheeler]

I had a similar problem a few years ago. I had a bad gasket on my strainer basket. At high RPM's it would suck in air and circulate less water. I made a new cork gasket and the problem went away.

Thanks. I'll definitely check this one.

 

[mz4wheeler]

Busy day today.

First, I cleaned out the seawater strainer (I cleaned it prior). This time, I vacuumed it out, cleaned the sight glass (so I could see bubbles), back flushed the intake hose (with a garden hose nozzle).

I then changed the thermostat. The old one looked OK... Almost original looking.

I also changed the impeller. It also looked perfect. Just to be extra safe, I checked the hose to the heat exchanger. All clear.

Fired it up, put it in gear and pushed it first to 2000 RPMs, then later to 2200 RPMs. It really put no significant strain on the dock/cleats/rope. After all, it's only an 18HP engine, and was nowhere near WOT. I did whirl up the marina. [grin]

Result (using laser temp probe), the thermostat housing hovered at 160 degrees (158-162), the block was up to about 178. The heat exchanger seawater input (80) output (95). The heat exchanger body was about 148.

The exhaust elbow (hot exhaust end) was about 220. The top of the elbow was about 110 (water end).

I then put my hand on the exhaust water, and it was surprisingly cool to touch.

So, I'm cautiously optimistic. I really won't know for sure until I run it again.

BTW: Took the old thermostat home and did the old boil test. It seemed to start opening at 170 (vice 160), so I'm hoping it was "stuck". Hard to say.

 

[Ralph Johnstone]

Did you ever get it to 3000 RPM which was causing the hi temp. alarm previously ? We need further readings .

Don't keep us in suspense ! ! ! ! You've (we've) got to figure this one out. I'm leaning towards a dirty heat Xchanger. Any bets ? ? ? ?

 

[Daveinet]

You could try running a ground.

 

[mz4wheeler]

Don't keep us in suspense ! ! ! ! You've (we've) got to figure this one out. I'm leaning towards a dirty heat Xchanger. Any bets ? ? ? ?

Sorry to keep you in suspense Ralph .

I'm going to take it out this week and run the hell out of it! I'm also [possibly] thinking dirty heat exchanger. If it still runs hot, I was thinking about this "minimal" approach.

Take off front panel (only) of the heat exchanger and try wire brushing the ports. Access to the back is more difficult. The boat has spent the last 2 years in salt water, and the previous 13 years moored fresh water.

Thanks to all!

 

[Ralph Johnstone]

Just a Note ..................

The boat has spent the last 2 years in salt water, and the previous 13 years moored fresh water.

............................. to add to your data base of inconsequential information, our boat 1999, has been in salt water for 16 years with no sign of fouling in the heat Xchanger (3600 RPM for 10 minutes @ 178 deg.). I'd expect yours to be pristine after the life it's lead.

Please keep us up to date as to what the hell bent load test produces.

 

[heritage]

Wow... I would think this could damage the cutlass bearing (my worry). However, it would certainly test the drive train under extreme stress.

I would not worry about the cutlass bearing being damaged due to the lack of water flowing through it. Many boats have the bearing imbedded into the hull where water flow from the movement of the boat is not there for cooling. Also, the suction created by the prop should pull water through an externally mounted cutlass bearing.

 

[mz4wheeler]

Did you ever get it to 3000 RPM which was causing the hi temp. alarm previously ? We need further readings .

Don't keep us in suspense ! ! ! ! You've (we've) got to figure this one out. I'm leaning towards a dirty heat Xchanger. Any bets ? ? ? ?

Ran it a 3000 RPM today, and sure enough, my trusty laser temp probe sensed the top of the thermostat at 195 (and rising), so I backed down the RPMs. What temperature should it be?

I am spitting out cool water (Puget Sound is about 60 degrees) out of the exhaust.

Heat exchanger?

I do have a red-dot heater in the loop, with valves to isolate. One thing I haven't tried is to shutoff that circulation. Not sure if that would make a difference.

I'm also going to replace the radiator cap and double-check the antifreeze/water mixture.

All this before I dig into the heat exchanger.