1978 GB32 - FL120 RPM issue and coolant leak

[ramkay]

Hello everyone.

I need some help with your expertise on an 1978 FL120 engine. I am living in the Paris region in France and my GB32 is on the river. Lately, I haven't been able to exceed the 2000RPM mark, down from 2350RPM I used to get previously. When I run the engine cruising at up to 1800 RPM, the temperature stays quite at the normal level of about 80°C or 176°F. The sooner I push the throttle upwards to its max, I'm unable to get more than 2000RPM and the temperature starts to go up rather quickly within a few minutes. I was never able to cruise at more than 1800RPM anyway previously, because of that temperature issue, even though I used to get up to 2350RPM. In addition, every time I cruised, even at normal temperature, I've noticed quite a bit of coolant in the pan under the engine and it is not leaked from the top cap, and I have to top off every time to make up for that loss. As far as the oil level is concerned, it remains the same and no traces of coolant is found there, which is a good thing, I suppose.
So, my questions to you my fellow trawler gurus are:

1. What's the maximum RPM a FL120 on a GB32 can get up to and keep the temperature at a normal level?
2. Why am I not able to get more than 2000RPM? Could it be a fuel injector problem or something else?
3. What might be the cause of the coolant leak? Could it be a circulating pump problem or a head gasket issue?
4. What might be the cause of the temperature spike? Could it be a defective thermostat?

So many questions. I'd really appreciate your feedback guys

 

[Comodave]

As to the coolant leak you could put some dye into the coolant. Then use the UV light to see where it is leaking. This is the kit I got from Amazon .

Mastercool 53351-B Professional UV Leak Detector Kit with 50W Mini Light, Black​

 

[ramkay]

As to the coolant leak you could put some dye into the coolant. Then use the UV light to see where it is leaking. This is the kit I got from Amazon .

Mastercool 53351-B Professional UV Leak Detector Kit with 50W Mini Light, Black​

Thanks Comodave

 

[DW1979OA]

Does you engines go to full rpms under a no load condition? Guessing it does and that the rpm issue is under loaded conditions.
Non the less my FL120s are of a similar vintage. In my case I also have over temp issues when I push the throttles up. But I know the reason on my boat is because it is over propped and also the bottom and running gear get nasty with growth very quickly where I’m at. A clean bottom allows more rpms and speed.
Next time you get hauled pull the props and have them tuned up. That and a clean bottom should help. Also make sure your throttle cables are adjusted so that you do get maximum at the engine
jp

 

[ramkay]

Does you engines go to full rpms under a no load condition? Guessing it does and that the rpm issue is under loaded conditions.
Non the less my FL120s are of a similar vintage. In my case I also have over temp issues when I push the throttles up. But I know the reason on my boat is because it is over propped and also the bottom and running gear get nasty with growth very quickly where I’m at. A clean bottom allows more rpms and speed.
Next time you get hauled pull the props and have them tuned up. That and a clean bottom should help. Also make sure your throttle cables are adjusted so that you do get maximum at the engine
jp

Thanks jp. Yes the engine goes beyond 2500RPM in no load mode. However, this situation arise rather suddenly after the annual engine oil, fuel injector pump oil and coolant change. The bottom was treated not long ago and I've been navigating in fresh water all along, so the growth is minimal. Throttle cables were adjusted as well this past summer. Strange!

 

[Comodave]

Did the RPM issue occur after the throttle cable adjustment or before?

 

[Mambo42]

If you can still get to 2500 rpm under no load then it is an issue with the prop or the rest of the running gear. I have the same issue, but I know it is a prop issue, cannot even get above 1900 rpm.

As for the temperature rise when increasing rpm. According to De Schiffart in the Netherlands (FL experts) the temperature should rise when you increase rpm, but after about 5 to 10 min the thermostat should open up again and then you should see the temp come back to normal again. If that does not happen then you have indeed a cooling problem. That could be the thermostat, a blockage in the cooling somewhere, not enough raw water running trough the coolers.
Like Comodave already said, try to find the origin of the leakage and another thing you can do is measure the temperature of the engine with an IR meter. That will give you a good indication whether you have any hot spots in the engine on places where they should not be.

 

[Bmarler]

Does the engine have a coolant recovery tank, or just a cap on an engine mounted header?
You may be adding coolant to a header tank that is supposed to have room for expansion and it’s coming out the overflow.

 

[ramkay]

Did the RPM issue occur after the throttle cable adjustment or before?

No Comodave, I did the cable adjustment after noticing the RPM issue

 

[ramkay]

If you can still get to 2500 rpm under no load then it is an issue with the prop or the rest of the running gear. I have the same issue, but I know it is a prop issue, cannot even get above 1900 rpm.

As for the temperature rise when increasing rpm. According to De Schiffart in the Netherlands (FL experts) the temperature should rise when you increase rpm, but after about 5 to 10 min the thermostat should open up again and then you should see the temp come back to normal again. If that does not happen then you have indeed a cooling problem. That could be the thermostat, a blockage in the cooling somewhere, not enough raw water running trough the coolers.
Like Comodave already said, try to find the origin of the leakage and another thing you can do is measure the temperature of the engine with an IR meter. That will give you a good indication whether you have any hot spots in the engine on places where they should not be.

Thank you Mambo 42. If I leave it running at full throttle (2000RPM presently) the temperature will reach 100°C+ in less than 10 minutes. I suspect that the thermostat is defective. Therefore, I am planning on recalibrating the fuel injectors and the fuel injection pump, as well as replacing the thermostat, the coolant recirculating pump and the head gasket, just got them from American Diesel. I will also be ordering the IR meter that Comodave mentioned.

 

[ramkay]

Does the engine have a coolant recovery tank, or just a cap on an engine mounted header?
You may be adding coolant to a header tank that is supposed to have room for expansion and it’s coming out the overflow.

Thank you Bmarler. Attached is a pic of the the coolant tank system on the engine. At high RPM it starts to burp and bubble and then overflows from the discharge hose that goes into the pan under the engine. I don't think the thermostat is opening. In the first photo at the bottom is the pan full of fluid and I see the coolant color on the coolant circulating pump which implies that the coolant stripped the red paint.

 

[Mambo42]

Thank you Mambo 42. If I leave it running at full throttle (2000RPM presently) the temperature will reach 100°C+ in less than 10 minutes. I suspect that the thermostat is defective. Therefore, I am planning on recalibrating the fuel injectors and the fuel injection pump, as well as replacing the thermostat, the coolant recirculating pump and the head gasket, just got them from American Diesel. I will also be ordering the IR meter that Comodave mentioned.

If it reaches 100 degrees C and also starts to push out engine coolant then your engine is overheating. What does your exhaust look like ? I am almost getting the idea you have a blown cylinder head gasket. I cannot see on the pictures where the origin is of the leakage. Obviously it comes from a higher location, but that is not clear in the pictures.

 

[ramkay]

If it reaches 100 degrees C and also starts to push out engine coolant then your engine is overheating. What does your exhaust look like ? I am almost getting the idea you have a blown cylinder head gasket. I cannot see on the pictures where the origin is of the leakage. Obviously it comes from a higher location, but that is not clear in the pictures.

My dilemma is that even at a normal temperature of 80°C I still have coolant leakage. The exhaust has hardly any smoke at up to 1500RPM, and when I go above it's a light white smoke like water vapor. The next day oil check is clear and clean. I'll try to get a better pic of the leakage area.

 

[captnscott]

Hello everyone.

I need some help with your expertise on an 1978 FL120 engine. I am living in the Paris region in France and my GB32 is on the river. Lately, I haven't been able to exceed the 2000RPM mark, down from 2350RPM I used to get previously. When I run the engine cruising at up to 1800 RPM, the temperature stays quite at the normal level of about 80°C or 176°F. The sooner I push the throttle upwards to its max, I'm unable to get more than 2000RPM and the temperature starts to go up rather quickly within a few minutes. I was never able to cruise at more than 1800RPM anyway previously, because of that temperature issue, even though I used to get up to 2350RPM. In addition, every time I cruised, even at normal temperature, I've noticed quite a bit of coolant in the pan under the engine and it is not leaked from the top cap, and I have to top off every time to make up for that loss. As far as the oil level is concerned, it remains the same and no traces of coolant is found there, which is a good thing, I suppose.
So, my questions to you my fellow trawler gurus are:

1. What's the maximum RPM a FL120 on a GB32 can get up to and keep the temperature at a normal level?
2. Why am I not able to get more than 2000RPM? Could it be a fuel injector problem or something else?
3. What might be the cause of the coolant leak? Could it be a circulating pump problem or a head gasket issue?
4. What might be the cause of the temperature spike? Could it be a defective thermostat?

So many questions. I'd really appreciate your feedback guys

Coolant leak because of over heating. Change thermostat, check belts, and if your dripping from waterpump(not impeller) it's time for a waterpump. Rpm are.2500 I believe. I cruise at 1800. White smoke indicates head gasket. When was the last time the impeller was changed. Also I have found on my engine that the sending unit fail. Take a hand held temp gauge and check water temp in reservoir.

 

[ramkay]

Coolant leak because of over heating. Change thermostat, check belts, and if your dripping from waterpump(not impeller) it's time for a waterpump. Rpm are.2500 I believe. I cruise at 1800. White smoke indicates head gasket. When was the last time the impeller was changed. Also I have found on my engine that the sending unit fail. Take a hand held temp gauge and check water temp in reservoir.

Thanks captnscott. I cruise at 1800RPM too and everything is normal as far as temp and oil pressure, the only thing is that the leak comes from the coolant circulating pump located under the coolant reservoir. The Jabsco raw water pump is functioning perfectly and I religiously change the impellers every year and the latest was done back in July. Do you ever get to 2500RPM and how long before it heats up?

 

[Mambo42]

My dilemma is that even at a normal temperature of 80°C I still have coolant leakage. The exhaust has hardly any smoke at up to 1500RPM, and when I go above it's a light white smoke like water vapor. The next day oil check is clear and clean. I'll try to get a better pic of the leakage area.

To me it sounds like a blown head gasket. The exhaust gases are blown into the coolant raising the pressure and thereby pushing the coolant out. When you increase rpm more heat is added to the coolant (via the head gasket) and that causes the coolant to start boiling. At that moment there is nothing to do for the raw water pump, the heat that comes out of the cylinders is much more than what the raw water can cool down.

 

[Bmarler]

I can’t tell from the photo, but it doesn’t look like there’s a coolant recovery tank anywhere. If that’s the case, the coolant level in the header should be at least an inch below the cap when cold so there’s room for expansion.
I tend to agree however, that there’s not enough coolant flow, either due to a faulty thermostat or coolant circulating pump. If the coolant isn’t flowing enough around the cylinder bores, the heat of combustion will vaporize the coolant at the cylinder walls and create the bubbling and burping you describe. There should be a thermostat bypass passage to allow the trapped air to escape and also allow low speed running if thermostat fails closed. Many times the bypass passage is providing enough flow if the raw water supply is nice and cool, and the thermostat won’t really even open till you throttle up and make more heat.
Changing the thermostat is the obvious first course of action. Be sure to do a temperature test on the new one to be sure it’s opening as expected before installing it.
Put it in a pan of water with a candy thermometer and bring it up to temp. Note the opening temperature to see if it matches the spec of the stat.

 

[Bmarler]

One more thought, if the circulating pump is leaking, or coolant is exiting the weep hole, you may be pulling air in as well as losing coolant. That can cause bubbling or burping as well.

 

[SteveK]

One more thought, if the circulating pump is leaking, or coolant is exiting the weep hole, you may be pulling air in as well as losing coolant. That can cause bubbling or burping as well.

you beat me to this conclusion. I had to change a coolant pump for that reason.
The OP said leaking from the coolant overflow hose, but I did not see a hose coming out from under the rad cap) it may be out of view). As was said there is no visible coolant recovery tank. Does not appear to be a leak around the rad cap.

Also, when filling the expansion tank do you open the air bleeder on top of the manifold and fill until water comes out?