2GM20F Engine overheating

Bill Roosa · Jun 9, 2015

The heat exchanger has no moving parts, the thermo does. I'd start with the thermo, test it in a pot of water on the stove with meat thermo. Should start to open at the temp stamped on the thermostat. Should be full open about 10-15 degrees hotter. Also check to see that it closes at the right (same as opening) temp as the water cools.

woodster · Jun 9, 2015

you may need to pull the end of the heat exchanger and remove some rubber from where the impeller was damaged on your water pump but first take the water hose going from the raw water pump off and see if it has a clog in it if not then on to the heat exchanger

Steve Dion · Jun 9, 2015

I am with the Woodster on cleaning out the heat exchanger. If you had a damaged impeller there is a good chance that some of those parts in stuck in the tubes.

heritage · Jun 9, 2015

Do you have a good amount of water spitting out of the exhaust?

Rick · Jun 9, 2015

Before you get out your tool kit, take a trip to harbor freight tools and buy yourself a thermal reading gun with the little "lazer" on it! Get ready to save yourself some time. I love them because when I making my rounds motoring, I can use the gun to tell me a bunch about my trusty "iron genny". Have some fun learning how to use it, lol, most belly buttons chime in at about 88 degrees!

The obvious, do you have water flow out your exhaust? That will tell you everything about the flow of water from that seacock you mentioned, through your raw water loop, and then overboard. If it is flowing, your not totally clogged BUT it may not be enough. That is critical.

You have an antifreeze loop. Good. How many hours on your engine? Probably in the 1000 hour range depending on your waters, it is time for an acid dip. However, that is a pain in the ass job.

So maybe a few IMHO ideas before you do the afore mentioned. You mentioned a nice stream at the seacock. Well where that tube next plugs should be your raw water strainer. Loosen the wingnuts and pull it out. Clean? Yes move on, no... clean it out and start her up. Bring her up to temperature and get out your gun. Or as you said bout five minutes or so. The seawater from your strainer to your raw water pump and up into the exchanger is not going to see big changes. Your antifreeze temp at several places is gonna tell you a bunch.

So in no particular order you need to check your thermo as mentioned. Shoot it with your gun, shoot the hose on both sides of it. It should be a 160 degree thermo so it should be pretty close when you shoot it. The coolant on either side of it should show some difference in temps. The hot side will be what just circulated through the engine and the cool side what just went through the exchanger.

Now find your way back to your mixing elbow. Its on the back of the engine. Its the exhaust pipe. So the hot exhaust is mixed with seawater in the mixing elbow to cool it so you dont melt your exhaust hose. Shoot it on both sides where the little water line from your exchanger screws into it. I forget the temp range but it should be a significant difference on either side. What happens over time to a mixing elbow is it basically gets heart disease and your seawater will not flow through it. But it being clogged is a different show.

This should give you an idea of where to start. IMHO, thermostats are to simple to fail and a pain to take out and test, but that is not to discount the expertise of ANY of the above posters. Some are better with tools than others.

So to sum up. Raw water seacock, raw water strainer, impeller, through exchanger housing, mixing elbow, water in exhaust.

Antifreeze loop. Temperature out of exchanger to engine , through engine and back to thermo.

Edit: Do you have a hot water heater that works from running your engine. Yep that is in the antifreeze circuit.

Damn I wish I had my engine to look at. Hopefully some of the guys will help make this easier to digest.

Cheers and good luck

woodster · Jun 9, 2015

admorton said:
Thanks, I will check the heat exchanger for debris. When I was changing the impeller, I forgot to close the sea-cock, and I experienced steady flow, so line is not blocked.

check the line going from the pump to the heat exchanger also

Rick · Jun 9, 2015

Read my post above.

Certainly not expert.

Just trying to save you from a fit. I just believe in a "more than one step post"

Ken Cross · Jun 9, 2015

Cleaning your heat exchanger

I fouind on my 2GM20F that a 22 caliber gun cleaning rod with a bore brush fit perfectly. I didn't even remove it from the engine, just removed both caps and cleaned it out. It was a snap once I finally got everything apart.

Ken

woodster · Jun 9, 2015

Ken Cross said:
I fouind on my 2GM20F that a 22 caliber gun cleaning rod with a bore brush fit perfectly. I didn't even remove it from the engine, just removed both caps and cleaned it out. It was a snap once I finally got everything apart.

Ken

yes it does

Ralph Johnstone · Jun 9, 2015

A mixing elbow like this isn't the best thing for cooling water flow.

BRIAN OCONNOR · Jun 10, 2015

I had the same problem as you. I did all of the above but the last thing I did was remove the 90 degree fitting to the Mixxing Elbow. It was cloged. I cleaned it out and it is fine. It's been good now for the last 2 years. Good luck.

B.T.O.

Kh3412 · Jun 10, 2015

I found that when fixing things it is always the last thing I check that is the problem. So I try to work backward but, the problems are smarter then me and always switch around so it is the last thing again. Maybe if I work with the lights off they won't know.....

Ralph Johnstone · Jun 10, 2015

Got the Same Problem ....................

Kh3412 said:
Maybe if I work with the lights off they won't know.....

..................... and you just may be on to something.

Ken13559 · Jun 11, 2015

Kh3412 said:
I found that when fixing things it is always the last thing I check that is the problem. So I try to work backward but, the problems are smarter then me and always switch around so it is the last thing again. Maybe if I work with the lights off they won't know.....

I know how it is. Been there. So to avoid it being last thing you do that fix it, why not after that repair, go fix something that isn't broken then that broken fix isn't last anymore.

Am I smart or am I....

Ken Cross · Jun 12, 2015

Ken13559 said:
I know how it is. Been there. So to avoid it being last thing you do that fix it, why not after that repair, go fix something that isn't broken then that broken fix isn't last anymore. Am I smart or am I....

I like it!

Ken

woodster · Jun 12, 2015

Ken13559 said:
I know how it is. Been there. So to avoid it being last thing you do that fix it, why not after that repair, go fix something that isn't broken then that broken fix isn't last anymore. Am I smart or am I....

well now that goes against the man law ...if it ain't broke don't fix it...it also cut in to the beer time

pvtpotter · Jun 12, 2015

Rick said:
Before you get out your tool kit, take a trip to harbor freight tools and buy yourself a thermal reading gun with the little "lazer" on it! Get ready to save yourself some time. I love them because when I making my rounds motoring, I can use the gun to tell me a bunch about my trusty "iron genny". Have some fun learning how to use it, lol, most belly buttons chime in at about 88 degrees!

The obvious, do you have water flow out your exhaust? That will tell you everything about the flow of water from that seacock you mentioned, through your raw water loop, and then overboard. If it is flowing, your not totally clogged BUT it may not be enough. That is critical.

You have an antifreeze loop. Good. How many hours on your engine? Probably in the 1000 hour range depending on your waters, it is time for an acid dip. However, that is a pain in the ass job.

So maybe a few IMHO ideas before you do the afore mentioned. You mentioned a nice stream at the seacock. Well where that tube next plugs should be your raw water strainer. Loosen the wingnuts and pull it out. Clean? Yes move on, no... clean it out and start her up. Bring her up to temperature and get out your gun. Or as you said bout five minutes or so. The seawater from your strainer to your raw water pump and up into the exchanger is not going to see big changes. Your antifreeze temp at several places is gonna tell you a bunch.

So in no particular order you need to check your thermo as mentioned. Shoot it with your gun, shoot the hose on both sides of it. It should be a 160 degree thermo so it should be pretty close when you shoot it. The coolant on either side of it should show some difference in temps. The hot side will be what just circulated through the engine and the cool side what just went through the exchanger.

Now find your way back to your mixing elbow. Its on the back of the engine. Its the exhaust pipe. So the hot exhaust is mixed with seawater in the mixing elbow to cool it so you dont melt your exhaust hose. Shoot it on both sides where the little water line from your exchanger screws into it. I forget the temp range but it should be a significant difference on either side. What happens over time to a mixing elbow is it basically gets heart disease and your seawater will not flow through it. But it being clogged is a different show.

This should give you an idea of where to start. IMHO, thermostats are to simple to fail and a pain to take out and test, but that is not to discount the expertise of ANY of the above posters. Some are better with tools than others.

So to sum up. Raw water seacock, raw water strainer, impeller, through exchanger housing, mixing elbow, water in exhaust.

Antifreeze loop. Temperature out of exchanger to engine , through engine and back to thermo.

Edit: Do you have a hot water heater that works from running your engine. Yep that is in the antifreeze circuit.

Damn I wish I had my engine to look at. Hopefully some of the guys will help make this easier to digest.

Cheers and good luck

Nice write up

a65sailor · Jun 13, 2015

If you pull the end covers off of the heat exchanger take it to a radiator shop and have it cleaned. If your going through the work make sure it's clean before buying new gaskets.

2GM20F Engine overheating

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