Perkins 4-108 0verheating

Remove the rear block core plug [freeze plug] and check the block for sand or mud buildup. The brass plug costs about $2. I have seen some block stopped up.

 

I don't think my fuel cost is going up much NOW that I have the right prop. In this case, the sailboat has a Trawler hull. This is on a Gulfstar 36 which used the same hull as the 36 foot Gulfstar trawler of the same vintage (3.5' draft).

 

I will check that plug next time I am at the boat. Its definitely worth doing but I think the Prop change was the main solution as I am no longer overheating.

Thanks for that suggestion, its one I hadn't heard and as I say will be checking next opportunity

 

the sailboat has a Trawler hull.

Actually you have it backwards , the Trawler got to be built on an existing sail hull.

This is GOOD as the sail hull is optimized for slow speeds , "trawler hulls" tend to be optimized for the add brochure "9K under power" but never mention its at 9 gal /hr.
The sail hull has less initial stability , so feels worse stepping aboard at the dock , but has a far finer, easier motion in 4 ft and up waves .

FF

 

I noticed on your posting that you have a Perkins 4-108 Diesel. I also have a Perkins 4-108 Diesel Engine on my 35’ sloop and I want to replace the thermostat. There is a cast Surge Tank mounted on the top front of the engine running from left to right, with a radiator-type fill cap mounted on top and with only 1 hose going out of the right back-side of the Tank into the Exhaust Manifold.

The Thermostat is apparently located under the surge tank. No problem in getting the Surge Tank off since it is held in place by a threaded rod coming up through its top capped with a nut. But when I begin to lift the tank slightly, engine coolant begins to seep out. I can and will remove all the engine coolant before I continue any further but my real question is:

1. Is it possible that the metal bottom Surge tank is acting, by itself, as a gasket on the top of the thermostat? This seems unlikely since in any typical engine I’m familiar with, any thermostat is sealed in its housing with a gasket and screwed on flange of some sort.

Do you have a similar arrangement with a surge tank that sits on top and crosswise on the top front engine of the Thermostat thus requiring this tank to be removed to remove the thermostat? Is your Thermostat mounted under this tank and does it have a gasket and covering it?

Delphi@iwlink.com

 

No, thank God, I dont have the model with the coolant tank across the front. It sounds like a real hassle.

Mine is alongside the Port side of the engine and the thermostat is easily accessed by removing two nuts and removing the gooseneck that holds the thermostat in place just like engines have been doing for many years.

Are you sure the thermostat is not aft of the coolant tank where it is accessable without removing the tank??

 

I read the thread and didnt notice this but ,,,what about a collapsing hose on the intake side?,,at higher rpm this can happen ,,and when you back off to see ,and look at it,it springs back to normal ,,and lets water flow.....longliner

 

Perkins 4-108 Overheating

For years I was plagued by the same problem you describe. I too replaced and cleaned everything related to the cooling system, ioncluding the fresh water pump, with no luck in finding the problem. It was not until I found an exhaust leak and unrapped the exhaust pipe that I fould the problem, exhaust restriction. This was creating too much back-pressure and causing the engine to overheat. I found that the previous owner had replaced the ehaust pipe and the first parts of it were a 4" pipe nipple into a 90 degree pipe elbow, both 1 1/2" pipe. I had a new pipe made from 2" stainless and my engine temp dropped about 10 to 15 degrees. You may not have the pipe problem, but maybe some sort of other restriction causing the problem. My engine now has much more power than before. If you have any questions, e-mail me at ahdalex@bellsouth.net and I will try to help.

Alex

 

I solved the problem quite a while ago. The answer was to put on the right prop. The PO had a 19x18 prop on it. I put an 18x13 prop on it and all is well now.

 

Glad you got it fixed

I guess it just goes to show that "things are not always what they seem". Anyhow, maybe my post will help someone look somewhere they hadn't thought of. I would have never guess that changing the exhaust pipe would solve my problem, but it did. Good sailing and fair winds!

Alex

 

I came across a similar problem some months ago. Turned out that the head was slightly warped. Machining the head and refitting with a new thicker head gasket solved the problem.

 

Overheating Perkins 4-108

We just went through a long process trying to figure out why our Perkins 4-108 engine was running hotter than it used to, and we finally figured it out! There is an L-shaped pipe that is the raw water return from the heat exchanger that mixes the raw water with the exhaust at the exhaust elbow. There is a flattened spray nozzle of sorts in the pipe that was almost completely blocked by small bits of the pencil zinc that goes in the heat exchanger. One of the symptoms was that there was more exhaust smoke than you would normally see coming out of the exhaust pipe. This smoky exhaust occurred at all RPMs. The temperature increased with RPMS, going up steadily to about 195 degrees at 3200 RPMs, then slowly rising after that. We could stop the rise by slowing down about 2500 RPMs. We discovered this after cleaning the heat exchanger, replacing the impeller and replacing the antifreeze. We were getting ready to change the thermostat...

 

David, speaking of pencil zincs, which bolthead on the heat exchanger is the zinc, and how often do you replace it? What size? I haven't replaced mine and have had the boat for two years now.

 

The 4.108 and all other Perkins marine engines did not have zinc pencils fitted as standard. Presumably they have never been used for exactly the reason described by David; they can break up and cause raw water flow problems. If the engine is properly bonded to the boat's main anode, zincs are not required. You will only find zincs on a 4.108 if the marinisation is non-standard or it has been modified to incorporate them.

 

Thanks pirate, that answers the question. I had looked in all of my Perkins manuals and information without finding reference to a pencil zinc and now I know why. I'm mechanically inclined but not so schooled in boats and galvonic corrosion, although I'm getting smarter by the day. Now if I can figure out why my boat eats it's shaft zinc in about three months time, I can rest easy for a while. Bonding system is the likely culprit, as mine seems to have had a less than professional installation by it's previous owners. Thanks again!