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Old 09-02-2013, 18:54   #1
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Perkins 4.108 Overheating While Under Load

We were under way and the temps suddenly started climbing so we limped back to the marina. When I opened the engine compartment, a considerable amount of coolant was in the bilge. We replenished the coolant supply (about a half gallon), ran it in neutral, and it was running at temperatures -- even at high RPM's. As we ran the engine, I checked the coolant lines for leaks and found none. We went back out on the river and it overheated again under load.

What perplexes me is that it does not seem symptomatic of a blockage. If there was a blockage, it would have overheated in neutral.

I'm thinking it might be a head gasket leak.

Any thoughts, advice, insight is much appreciated.
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Old 09-02-2013, 19:31   #2
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Re: Perkins 4.108 Overheating While Under Load

Is this engine new to you? Or has it run fine for a long time and just started this? I had a Perkins 4-154 that would be fine when not under load, but if run more than 1800 RPM under way, would over heat. I lived with it for years, but the next owner told me that he pulled the head and all of the cooling passages were clogged up from rust. When I bought the boat the rubber seal on both ends of the heat exchanger were leaking salt water over to the fresh water side. I suspect it had been that way for a long time and that is what caused the plugging of the cooling passages. If this is a new problem, then it is probably just a failed thermostat or the water pump">raw water pump has lost some vanes. Either one is easy to fix, and both are worth checking as regular maintenance.____Good Luck_____Grant.
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Old 10-02-2013, 10:33   #3
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The engine is new from British military surplus, manufactured in the 80's but never been put into service until October 2012. We went on a few short cruises and had no issues with overheating. This is the first incident of such.

FWIW, the coolant is brown, despite the fact that the engine has been flushed and new green coolant has been added just before being put into service.

The first thing I'm going to check is the heat exchanger and next comes the thermostat.
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Old 10-02-2013, 13:02   #4
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Re: Perkins 4.108 Overheating While Under Load

Auto parts stores sell kits for checking the pressure of a radiator, which is basically what the fresh water side of our cooling systems are. Some of the bigger parts stores may rent the tool. It just replaces the radiator cap(I think most Perkins have a pretty standard cap) and tells you if you have gases getting into your fresh water side, from a head gasket or a cracked head, or block. I think you are starting in the correct spot since 30 years on the rubber end fittings, without water may have made them very brittle. Is the brown color the same shade as the local water in your part of the delta. That would be another clue. Good Luck______Grant.
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Old 20-04-2013, 17:18   #5
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I just replaced the thermostat and took the boat out today. It started overheating. I came back to the dock and removed the thermostat. I placed the engine under load again, this time at the dock (in gear with dock lines tied) and running at 1500 RPM. Without the thermostat, it took longer for the engine temperature to rise; but sure enough, it hit 210-220 degrees.

As the engine was running, I checked my coolant reservoir (not coolant tank) and noticed it bubbling.

As I removed the thermostat, I also loosened the fanbelt to check the water circulating pump. It spun with a little amount of force, not freely...so I'm pretty sure the shaft is not disconnected from the impeller.

What shall I check next?
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Old 20-04-2013, 17:25   #6
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Re: Perkins 4.108 Overheating While Under Load

After I had the head off my 4-108, it overheated immediately. I found out that there was air in the cooling system right under the thermostat housing. The thermostat wouldnt open up because it was surrounded by trapped air not water. I had to remove the thermostat housing and pour in coolant to completely full and then replace the thermostat etc.
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Old 20-04-2013, 17:28   #7
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Re: Perkins 4.108 Overheating While Under Load

Why did you replace the thermostat?
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Old 20-04-2013, 17:29   #8
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There was no coolant under the thermostat, so I will do as you suggested and give it another shot.
Thanks!
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Old 20-04-2013, 18:27   #9
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Quote:
Originally Posted by sww914 View Post
Why did you replace the thermostat?
I removed the original thermostat and tested it. It did not move no matter what temperature I exposed it to.
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Old 20-04-2013, 18:48   #10
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Re: Perkins 4.108 Overheating While Under Load

Retorque the head and see if that helps.
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Old 22-04-2013, 11:00   #11
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Re: Perkins 4.108 Overheating While Under Load

Cheechako, I did as you suggested. There was very little coolant in the block. I must have added about a gallon, before it topped off. I ran the engine under load and the the temperature stayed steady at 180, which is a good sign. Thanks for the suggestion!

However... Here is the other dilemma. The coolant overflow tank cap popped off shortly after the engine came to operating temperature. As the engine was running, I noticed the coolant in the overflow tank was bubbling. There seems to be air trapped inside the system. I removed the expansion tank again, checked the coolant level under the thermostat, and it was pretty full. Any additional coolant I poured would come out of the manifold, at the point where it connects to the expansion tank. This gives me some (not full) assurance there is no air trapped in the system. However, there was no coolant in the expansion tank when I turned the engine off and after it had cooled. I re-installed the thermostat and expansion tank. Topped off the expansion tank with coolant up to the neck.

I have not tested the engine yet. I bought a new cap for the expansion tank and will replace it tomorrow and run the engine.

Here is the 68 million dollar question... Was the bubbling in the coolant overflow reservoir likely to be air that was trapped in the coolant circuit? Or is such bubbling unheard of on the Perkins 4.108, which would lead me to want to check for exhaust gasses in the coolant...?
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Old 22-04-2013, 11:03   #12
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Re: Perkins 4.108 Overheating While Under Load

Not sure, I would run it for a while with the cap off and see if the bubbling stops... is it pretty agressive bubbling? Exhaust bubbling should have some color to it I imagine...if so, you may have a problem..... I'm leaning toward a problem if it popped the cap off....
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Old 22-04-2013, 13:36   #13
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Re: Perkins 4.108 Overheating While Under Load

Quote:
Originally Posted by Astral Blue View Post
Cheechako, I did as you suggested. There was very little coolant in the block. I must have added about a gallon, before it topped off. I ran the engine under load and the the temperature stayed steady at 180, which is a good sign. Thanks for the suggestion!

However... Here is the other dilemma. The coolant overflow tank cap popped off shortly after the engine came to operating temperature. As the engine was running, I noticed the coolant in the overflow tank was bubbling. There seems to be air trapped inside the system. I removed the expansion tank again, checked the coolant level under the thermostat, and it was pretty full. Any additional coolant I poured would come out of the manifold, at the point where it connects to the expansion tank. This gives me some (not full) assurance there is no air trapped in the system. However, there was no coolant in the expansion tank when I turned the engine off and after it had cooled. I re-installed the thermostat and expansion tank. Topped off the expansion tank with coolant up to the neck.

I have not tested the engine yet. I bought a new cap for the expansion tank and will replace it tomorrow and run the engine.

Here is the 68 million dollar question... Was the bubbling in the coolant overflow reservoir likely to be air that was trapped in the coolant circuit? Or is such bubbling unheard of on the Perkins 4.108, which would lead me to want to check for exhaust gasses in the coolant...?
The coolant capacity of the 4-108 is about two gallons. That will increase slightly by the amount of coolant contained in the heat exchanger. The cooling system cap should be sized to provide 10 to 14 psi of operating pressure. Any air entrained in the cooling system will expand and assuming the coolant pump is operating normally will shortly be expelled from the system via the pressure cap. Under normal circumstances, the coolant mix will expand by approximately 6% or approximately 15.3 ounces as the engine operates normally. This expansion of coolant is accommodated by the expansion tank which should be sized accordingly but is not, normally pressurized. Hot coolant is captured by the expansion tank and then returned to the cooling system as the engine temperature cools. If your expansion tank is not large enough to accommodate the amount of coolant that may be expelled from your engine at normal operating temperature, the excess will be lost--perhaps popping the cap off the expansion tank--but then, with an undersized tank, insufficient coolant will allow air to be returned to the cooling circuit as the engine cools. So long as the expansion tank is under sized, you can find yourself repeating the fill, overflow, deficiency, refill cycle ad nauseam.

FWIW...
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Old 22-04-2013, 19:12   #14
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Re: Perkins 4.108 Overheating While Under Load

My 4-108 didnt have an expansion tank at all. just a tube going to the bilge. Never used any coolant to speak of.
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Old 22-04-2013, 22:08   #15
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Re: Perkins 4.108 Overheating While Under Load

Quote:
Originally Posted by svHyLyte View Post
The coolant capacity of the 4-108 is about two gallons. That will increase slightly by the amount of coolant contained in the heat exchanger. The cooling system cap should be sized to provide 10 to 14 psi of operating pressure. Any air entrained in the cooling system will expand and assuming the coolant pump is operating normally will shortly be expelled from the system via the pressure cap. Under normal circumstances, the coolant mix will expand by approximately 6% or approximately 15.3 ounces as the engine operates normally. This expansion of coolant is accommodated by the expansion tank which should be sized accordingly but is not, normally pressurized. Hot coolant is captured by the expansion tank and then returned to the cooling system as the engine temperature cools. If your expansion tank is not large enough to accommodate the amount of coolant that may be expelled from your engine at normal operating temperature, the excess will be lost--perhaps popping the cap off the expansion tank--but then, with an undersized tank, insufficient coolant will allow air to be returned to the cooling circuit as the engine cools. So long as the expansion tank is under sized, you can find yourself repeating the fill, overflow, deficiency, refill cycle ad nauseam.

FWIW...
Thanks for the explanation. I'm almost breathing a sign of relief based on this assessment, feeling increasingly confident it is not a head gasket or manifold leak.

Based on the bubbling, I have a feeling there is still some room for more coolant. I'm going to let this go on for a few sessions and constantly monitor the level of the expansion tank. I'm pretty sure the level will go down considerably as air is being displaced.

Quote:
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My 4-108 didnt have an expansion tank at all. just a tube going to the bilge. Never used any coolant to speak of.
I'm guessing you're referring to the coolant overflow reservoir, and not the cast aluminum tank that connects to the manifold and sits on top of the thermostat...right?

I'm off the the boat tomorrow to put the plan in action. Keeping my fingers crossed!

Thanks everyone for the helpful advice!
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