Perkins 4108 thermostat

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neil1967

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The temperature on my perkins 4108 fitted to my Oyster 406 varies a bit - ie it goes up under load, so I am considering replacing the thermostat - we've only had the yacht for a year so I don't know how old the thermostat is. Question is, do I need a thermostat with bypass, or without? Unfortunately I'm a couple of hours from the boat, and would like to order one for next weekend so I can fit it. Any ideas much appreciated - the engine was installed in 1987.

Thanks

Neil
 
the coolant will get hotter under load, that is quite normal


neil1967 said:
The temperature on my perkins 4108 fitted to my Oyster 406 varies a bit - ie it goes up under load, so I am considering replacing the thermostat - we've only had the yacht for a year so I don't know how old the thermostat is. Question is, do I need a thermostat with bypass, or without? Unfortunately I'm a couple of hours from the boat, and would like to order one for next weekend so I can fit it. Any ideas much appreciated - the engine was installed in 1987.

Thanks

Neil
Click to expand...
 
If the temperature only varies by a small amount its nothing to be concerned about. If under sustained high load the temperature rises excessively then the thermostat is one of the things worth checking.

Water inlet strainer , pump impeller, exhaust injection point and overall condition of hoses are all also items to check.

i assume the engine is indirectly cooled ??? if so the condition/cleanliness of the heat exchanger is also relevant.

The workshop manual at http://www.motoren.ath.cx/Download.php?filename=/perkins/Perkins-4.107_4.108_4.99.pdf shows both types of thermostat. The type required appears to depend upon whether or not the engine has an external bypass. The diagram on the last page of section M illustrates the system with an external bypass.

Be sure you get a thermostat with the correct opening temperature... the existing one should be marked
 
+1. This either works properly or not. As long as temperature stays inside acceptable range (80-100 C) no worries, don't fix if works.
What type of cooling system, exchanger and such - You have to establish, there are so many changes made to his engine that I'm lost already myself; some new kind parts were fitted later, on mine (older) only way is to take the part out and see...
 
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Thanks Vic & Sailorman. I am probably worried about nothing - the temp went up by about 5-10 degrees with an increase of about 500RPM over normal cruising speed/revs, but remained constant under the increased load. The online manual will be useful.

Thanks again

Neil
 
neil1967 said:
Thanks Vic & Sailorman. I am probably worried about nothing - the temp went up by about 5-10 degrees with an increase of about 500RPM over normal cruising speed/revs, but remained constant under the increased load. The online manual will be useful.

Thanks again

Neil
Click to expand...

If thats in degrees C I'd not be concerned about an increase of 5C . An increase of 10C perhaps something to keep an eye on. Its almost the full operating temp range of the thermostat
 
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Still no worries. Can't say for newer model engine, but perkins thermostat opens about 80 C, gradually; on engines with domestic water calorifiers the 70 C might have been fitted too.
Not to mention oil cooler to it, keeping the engine evidently too cold if not under good load...
 
Rossynant said:
Still no worries. Can't say for newer model engine, but perkins thermostat opens about 80 C, gradually; on engines with domestic water calorifiers the 70 C might have been fitted too.
Not to mention oil cooler to it, keeping the engine evidently too cold if not under good load...
Click to expand...

The Op does not say what the actual temperature readings are but according to the spec there is 14C difference in temp between just opening and fully open. A 10C variation is a significant proportion of that! Maybe its normal for this engine but IMO it would be wise to at least check the cooling water flow and if the variation increases the other items I mentioned earlier too.

Now is the time to check out the cooling system.... not wait until it overheats half way across the North Sea

Is there an oil cooler? Its not mentioned in the manual?
 
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Yes - and opening at 75-90 for instance still can get temps to 95 with no problem. As for specs I have quite a few manuals, each mentions couple of different set-ups. Originally they were direct cooled, later with 2-3 heat exchangers, later on there was combined "header/exchanger/exhaust manifold"; oil cooler was standard, but not necessary for UK use really so may be there or not.
Won't even try to answer OP's question since never looked for younger engine than mine :o Those engines were also produced in Poland, quite different form original UK version (not to mention metric threads) for land use so different cooling; and newer kind was used in Volkswagen Golf D cars, still different, with pressurized cooling so might have been working in 95-105 C for all I know.
On top of it thermostats for many engines can be had in any temperature characteristic, to suit. Who knows what is actually installed in OP's engine at the moment.
So don't even ask... :)

Heat exchanger is a bunch of copper tubes for seawater, can be scale build-up is there, good idea to flush; or cleaning would be advisable, but it's a bit of dismantling.
 
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Unless the OP knows that the water pump impeller is fairly new replacing it would me a wise move.
Even if it leads to no reduction in the temperature variation he will know that it is new and not likely to break up without warning due to age.
 
+1 for pump impeller,only remove the cover on the pump to change do not remove the pump from the engine as this is a hard job to get it re-centured
 
My 4-108 runs at 80 under most conditions but that's in Greece in pretty flat water. Pushing the revs a bit will only change it 2 or 3 degrees but really loading it, punching in to a f6/7 and swell head on, got it up to 90.

If you're running under 95 at all times and you don't see steam out of the exhaust you are fine. Exhaust steam is a sign of not enough water in the exhaust and points to intake filter or impeller problems ( or a closed seacock! )
 
replacing the thermostat on mine involves removing the header tank it sits in there, once this job is done and any hoses replaced which you will, then the impeller could be changed its under all of that lot.
Sounds like its running normal, but if you change these at least you will sleep at night.
 
Thanks for the advice and thoughts - I replaced the water pump (worn and leaking) and cleaned out the stack last year prior to sailing from the port of purchase (Ipswich) to our current mooring in Portsmouth. I am happy with the amount of water flow. I guess I was expecting that once up to temperature, the engine would keep at a constant temperature, as is the case in cars. I am re-assured that there does not seem to be a problem.

Neil
 
Not sure if I'm doing this right (first time posting!) I'm looking for any tips on removing the thermostat from a marine Perkins 4.236 with a closed circuit cooling system. No cooling problems; just noticed however, that the coolant has some globs of green "gel" (long time since it's been changed!) and I wish to do a thorough flushing with the thermostat removed so as to get full flow through the system. I removed the top water hose and plan to use a house supply water hose to force clean water backwards through the thermostat housing (sans thermostat) and with an exit drain hose attached to the cooler to avoid building up any pressure I have removed the thermostat housing, but the thermostat itself seems to be "pressed" down into the cavity and I cannot lift it out even with needle nose pliers (see photo attached). No corrosion to speak of, but I've tried Gibbs and PB Blaster to no avail. I do not wish to damage the thermostat trying to remove it!
Any ideas on how to remove the stat without damage would be appreciated!
Thanks!
7/10/2013: UPDATE: after spending over a week trying to figure this out, I realized that there’s a metal plate covering the whole area surrounding the thermostat! Some type of accessory mount. The thickness of this plate is why it appeared that the thermostat was pressed down into the block. Removing this plate (with some force, as it was held in place by the thermostat studs) revealed another thermostat gasket. Removed this and the thermostat lifted right out! Now I’ll do the back flush and put it all back together.
 
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