Perkins 4-108 Overheating ...

[KaptainKen]

I seem to remember a thread regarding a mysterious overheating problem that was narrowed down to a possible air lock in the portion of the fresh water (as opposed to "raw" sea water) engine coolant that is diverted to circulate through the hot water heater.

I tried the forum "search" feature with no success. Anyone remember where it is located?

Anyhow, I think I have the same problem. My 4-108 occasionally overheats to the point of locking up. This occurs even after a daily check of coolant level. The coolant apparently just "disappears". I'll check the coolant level in the morning, and at (say) noon the engine will overheat. It will take three of four "coffee-pot-fulls" of water to fill the engine and heat exchanger.

What it isn't: The heat exchanger core was cleaned and pressure tested. There is no coolant in the bilge; there is none of the the distinctive green color water present. The thermostat works; the engine temperature gage rises to 190 degrees and stays there when operating normally. I don't think its escaping through the exhaust ... at least I don't leave an "oily" sheen behind me. The "radiator" cap on the heat exchanger is new and rated seven pounds per Perkins specifications.

A fellow cruiser suggested installing an "expansion" tank as the highest point in the cooling system and then topping up the coolant there instead of through the regular "radiator cap" on the heat exchanger. Has anyone tried this? How do you plumb it in? How will this effect the usual 7 PSI that the cooling system operates with?

Sorry for the long post/question/request for help, but I've tried to cover the usual reply questions and requests for clarification.

Thanks!

[Maddog]

I had the same problem on my 4-107. There wsa an air block at the water temp sensor in the manifold,(highest part). Remove the sensor, top off with coolant, replace sensor with a litlle anti-seize on the threads. It has never overheated since.

[CSY Man]

Wow, if yer coolant disappears, not in the bilge, not in the exhaust..Then perhaps the through the Head Gasket?

My 4-108 overheats when ran over 2600 RPM for extended periods, never found the problem.
The coolant however is not leaking out.

[AnchorageGuy]

Ken, My Perkins had an oil cooler which was just a exchanger and it developed a leak. The next place to look is manifold. Your FW coolant is probably going out with the seawater somewhere. Expansion tanks are common and you can buy them at an auto supply store or marine engine shop/ Install it to the nipple on your FW fill cap if there is one there. If no nipple the install will be more difficult. The tank should be about even with your FW tank on the engine. The coolant if leaving with the exhaust is probably so diluted it may not be noticeable. Try catching a bucket of exhaust water and take a good look.

[AnchorageGuy]

just wanted to add, an airlock is not going to take 3 or 4 coffepot size fills on a regular basis.

[Maddog]

Originally Posted by Chuck Baier

just wanted to add, an airlock is not going to take 3 or 4 coffepot size fills on a regular basis.

This is correct.

[Maddog]

Originally Posted by CSY Man

Wow, if yer coolant disappears, not in the bilge, not in the exhaust..Then perhaps the through the Head Gasket?

My 4-108 overheats when ran over 2600 RPM for extended periods, never found the problem.
The coolant however is not leaking out.

Dude, what rpm to you usally cruise at? This is always a big question for the perkins guys?

I'm afraid to tell you what I cruise at.

[CSY Man]

I cruise at 2100 RPM. = 70% of max continous.
Gives me 5.2 knots or so.

If in a hurry, I go 2400, 5.6 knots.

At 3K I am at almost 7 knots, but the temp keeps climbing.

At 4K we move at warp speed with foam flying and the stern digging it, probably 7.5 knots and at hull speed.

Uh, what do ya cruise at??????

[Alan Wheeler]

Anyhow, I think I have the same problem. My 4-108 occasionally overheats to the point of locking up.

That maybe a possible right there. Yikes, you don't want to lock up a diesel. That can cause all sorts of damage.
I'll come back to that.

There is a possibility it is just expansion. This is what the overflow tank is for and you should have one. 7lbs is not a lot of pressure. Many engines are 13lbs. As the engine and water expand due to heat, the water has to go somewhere. So it dribles out the overflow undere the cap. As the engine cools down again, it sucks back in through the overflow under the cap. So it will leak out water and suck back in air. The overflow should go to a holding bottle and so the water blows out into the bottle and is then sucked back in. With out that, you will most likely replace about a coffee pot full of water each day.

If it is a cooling leak somewhere, you can pressure test the cooling system. There is an aperatus available that pressure tests the cooling system. You connect it and pump it up. The first thing that should happen is the radiator cap should lift at 7lbs pressure. That tests the correct operating pressure. Then you leave it pressurised over night and see if the pressure has remained. If it has gone to zero, then you have a leak somewhere. Either you will see the result of the leak if it is external, or you will have to go looking for it internaly. But the test will tell you if there is a problem.

Now back to the lock up from over heating. They are fairly robust engines due to having a cast iron head as well as block, but repeated siezing can still cause head gasket issues, not to mention damage to rings and pistons and liners and cranks and and and. You may have had an intial low water over heat to begin with and after the engine locked up, it may have now caused an actual fault that is allowign the coolant to escape through the exhaust. You are at a stage where you just may have to remove the head and check the gasket. If there has been damage to the gasket, it will only get worse till the point of where you will fill a bore with water and it will hydraulic when you try to start it one day. That will cause damage you don't want.

[KaptainKen]

Chuck: When you said "an airlock is not going to take 3 or 4 coffepot size fills on a regular basis." you are undoubtedly right. The only thing I can think of is associated with Maddogs "water temp sensor in the manifold,(highest part)".

If an airlock developed at the sensor and pushed the coolant back through the hoses and through the heat exchanger in the hot water tank it could conceivably amount to a couple gallons of coolant. Later, when the airlock "broke" and hot water heater system filled with coolant again the engine would be a couple gallons short of full. Possible? Could be. (Grasping at straws here.)

Per Maddog's sugestion I'm going to put a valve on the manifold where the heat sensor now is. I'll fill and/or "vent" the system at this point.

Thanks for your suggestions, gents.

(Ref: Cruising RPM: I usually run at about 2100 RPM. I get about 5 1/2 knots and burn about .8 or .9 gallons per hour.)

[KaptainKen]

Wheels;

Ref: " ...head gasket issues, not to mention damage to rings and pistons and liners and cranks and and and." Well, of course it has not done the engine any good to seize and lock-up. I can't undo a previous lock-up ... all I can do is try to prevent a future one.

I don't think coolant is getting from the water jacket to the cylinders. I have had the head off a couple times (repairing exhaust manifold stud problems) and have replaced the headgasket each time. I torque the head per Perkins specs including the recommended re-torque after a certain number of hours.

I like your suggestion of pressure testing. I think I can rent a pressure tester at a local auto parts retailer.

Thanks.

[Maddog]

Originally Posted by KaptainKen

Chuck: When you said "an airlock is not going to take 3 or 4 coffepot size fills on a regular basis." you are undoubtedly right. The only thing I can think of is associated with Maddogs "water temp sensor in the manifold,(highest part)".

If an airlock developed at the sensor and pushed the coolant back through the hoses and through the heat exchanger in the hot water tank it could conceivably amount to a couple gallons of coolant. Later, when the airlock "broke" and hot water heater system filled with coolant again the engine would be a couple gallons short of full. Possible? Could be. (Grasping at straws here.)

Per Maddog's sugestion I'm going to put a valve on the manifold where the heat sensor now is. I'll fill and/or "vent" the system at this point.

Thanks for your suggestions, gents.

(Ref: Cruising RPM: I usually run at about 2100 RPM. I get about 5 1/2 knots and burn about .8 or .9 gallons per hour.)

All good points - The other issue is, if there is an air lock at the water temp sensor, what is that sensor measuring? super heated air? Steam vapor? The width of my wide butt? who knows. I do know it was not measuring the temp of the cooling water. I would not fill the entire system from this point. When you change the coolant anually. Remove the sensor so it vents. When coolant comes out the top, screw it back in. Test the engine, if it over heats. Add more coolant at the sensor. Be sure to check it after the thermosat has opened. This has solved my problems.

Onto rpm's - I am over prop'd, I cruise at about 1600 at 5.5 knts top out at 1800 at 6 knts. I would like to cruise at about 2000 to 2200. this is the top of the torque curve for my engine. I have a 4-107, not the 4-108. I believe they are the same except for the size of the bolts on the manifold and other minor things.

What say the rest of you? Anybody cruise at less than 2000 rpm's?

[CSY Man]

Me thinks the difference between the 4-107 and the 8 was wet sleeves or not...?

If ya are over propped and only get 1800 RPM, ya may see soot and stuff on the transom from un-burned fuel..

I tried intentional over proping for a while, but found no benefits and changed back. (Have 2 props, have had both of them tweaked and adjusted to various pitch values..Easy for a prop-shop to do)

[Maddog]

Originally Posted by CSY Man

Me thinks the difference between the 4-107 and the 8 was wet sleeves or not...?

If ya are over propped and only get 1800 RPM, ya may see soot and stuff on the transom from un-burned fuel..

I tried intentional over proping for a while, but found no benefits and changed back. (Have 2 props, have had both of them tweaked and adjusted to various pitch values..Easy for a prop-shop to do)

I do. When I see the black smoke I know it's time to throttle down. I will redo the prop next time I haul.

[Alan Wheeler]

Yep redo the prop adn if you intend to do a lot of motoring, don't make that next haul to far away.

Inregards to the overheating topic, an air lock will not be the problem. The air bubble is not that big and once the engine has worked, it should flow through to the exhanger. Once that has happend and you top up, it should not happen again. For the water to continualy disapear, there is another issue. And it could be as simple as the water being forced out as the engine heats and the cap sucking air back in as it cools down.