Overheating Perkins 4108

[Guest]

Does anyone have experience with an overheating Perkins 4108?

We have purchased an Alden designed sloop with a Perkins 4108 motor. Unfortunately, the motor has turned out to be problemmatic. I am in Sydney, Australia and the boat is currently in Brisbane.

The motor is shutting down at approx 180 Deg F. Fresh water coolant is released via the header tank filler cap under pressure .

We have tried a number of checks without wanting to lift the motor out to resolve the problem but are so far unsuccessful. These include:
- cleaning the air filter
- fitting a new water filler cap
- removing the exhaust manifold and checking for cracks and fresh water leakage. There were none. The exhaust system appears free of restrictions.
- fitting a new sea water pump impellar - there is currently agood flow of sea water from the exhaust.
- we have been unable to remove the heat exchanger but this appears free of blockages.
- we are unable to examine thermostat at this stage as the header tank cannot be removed because the retaining bolts cannot be removed to dismantle it. They have frozen in.
- there is no apparant external coolant leakage between head and cylinder block
- we don't believe there are internal leaks as checks at this stage do not indicate internal leakage.

Is anyone able to suggest a course of action to find the problem or a way to remove the header tank retaining bolts without shearing them or rounding the heads? Alternatively, can anyone point us towards someone who might have the answers?

 

[Guest]

Could be your cylinder head gasket leaking combustion presure into the water jacket,the presure is coming from somewhere and at 180 deg this should not be causing a problem. Its unlikely but you could check seating under presure cap .
good luck
pete

 

[Guest]

Its unlikely to be the thermostat as they are manufactured to fail safe [ie open] but still its a possibility. I would have thought a compression test was the next thing to do, a big differance in pressures between cylinders could/would indicate a head gasket problem. I assume you have fully flushed the fresh water cooling system with a cleaning de furring solution.
As for the studs, tried heat on them? Even if it means lifting the engine you've got to get them out. If they break its an easy job to drill and re-thread them, but out they have got to come 'cos sods law says if they stay in they will be the cause of something 'orrible happening.

 

[Guest]

How old is the engine?
If it about 20 years old or more, it could be a cracked head.
The 4-108 is an indirect injection engine and on the older 4-108 engines, the groove directing the gases from the combustion chamber into the cylinder is cast into the head. On later models and virtually all other indirect injection engines, the groove is on the piston crown.
This groove in the head is prone to cracking. (along the corners of the groove). That's why they changed it.
Could be a head gasket though, if your luck is in!
Tom

 

[Guest]

I agree that thermostats are supposed to fail open, but mine failed closed last week.
So check your thermostat.
I've also known the tubes in a heat exchanger to scale up to an extent where there still appears to be a good flow, but the scaling prevents the heat transfer.