Perkins 120's

We have twin Perkins 120's on our 1978 Gulf Star 44' trawler. We have kept them well maintained and they operate fine. Cruising, we generally run them at about 1600 rpms. The question neither of the mechanics we have relied upon can answer is that at that speed the port engine runs consistently at about 120 - 130 degrees and the starboard at about 180. As stated, they both operate well but one of them is, it seems to me, not operating as efficiently as the other. We have been told that the 180 is more typical. It has also been suggested that as they revolve in different directions this may explain the difference but this seems questionable. Any thoughts appreciated.

180 sounds right- no thermostat in cooler engine possible? A thermostat is a temperature regulator- and it's probably not installed. What model Perkins??


1983 Present 42 Sundeck
Twin Lehman 135's

6.354 turbocharged.

K. Figured turbo for sure with that HP.


1983 Present 42 Sundeck
Twin Lehman 135's

Thanks. Will follow up on the thermostat suggestion.

Its possible the gauge is at fault. If you havent done it already I would suggest verifying the engine temps using an infra-red temp gun before you do anything to the engines. Get very close and point it at the thermostat housing. If the engines prove to actually be running at those temps then the thermostats are the first things to check because they are the parts that are supposed to regulate the temps.

Ken

Gauge was my first thought as well. The gauges on my old Gulfstar with twin 4-236 were not very accurate. readings were different between upper and lower helms, if you gave the gauge a good knock with your knucles it would bounce up or down 15 degrees. I just watched them for unusual readings and didn't worry about how accurate the temps actually were.

You may be able to tell from the gauge, if within a bull`s roar of accurate, if a thermostat is fitted. Slow to warm up, doesn`t reach full temp, temp rises with harder worked engine, drops at lower rpm, may mean none fitted. That`s how I discovered one was not fitted. It`s usually left out for a reason,engine gets hot with one fitted, indicating something is not right. Alternatively, it could be fitted but stuck open. You can test it, once removed put it in cold water which you heat on the stove, see if it is closed and then opens as the water gets hot.

Thermostats are cheap, unless you have Cummins, then there is 2 of the suckers. If you got it out just change it.

If it is 120 it's too cold, the engine is not happy at that temp, which is why you are supposed to warm with a load to speed through that range. Rotation is irrelevant for temperature (but not if a starter or water pump fails...($$$).

Yeah, the Perkins should operate at 180. There are good reasons why the temp. shouldn't stay below 180. I totally agree that you should check the gauge with an IR temp. gun. Then replace the bad thermostat.

If it's been several years, then the antifreeze should be changed as well, while you have the system open.

Then I'd recommend a full power run to ensure the heat exchanger can handle the heat at full load. Heat exchangers foul over time, and you don't want to discover you have a problem when you're trying to outrun weather.

The temp shouldn't exceed about 195 at full load. Some increase from idle to full load is normal - the thermostat needs about ten degrees increase to go to fully open.

I'm amused by the folks who will spend tens of thousands on a boat and then invent all sorts of excuses to avoid spending a hundred bucks on clean antifreeze.

go figure

Good Luck!

JS

henryj2 said:

We have twin Perkins 120's on our 1978 Gulf Star 44' trawler. It has also been suggested that as they revolve in different directions this may explain the difference but this seems questionable. Any thoughts appreciated.

Click to expand...

Henry:
Pretty sure the other posters are correct about your thermostat needing changing or temp gauge being inaccurate.

Also:
Early Perkins engines could be contra rotational, but by the late 70's with the advent of Velvet Drive series 71 and 72 trannies, Perkins dropped the contra rotational engines. The counter rotation of the propellers occurred in the transmission after that. The contra rotational engines had the letter "X" in the serial number prior to the beginning of the sequential number. I have a chart somewhere that breaks down the dates and engine numbers, but all you have to do is observe the engines running to confirm that they are turning the same direction.

Also the 120 HP rating you're quoting for a T or HT 6.354M is pretty low. The 6.354M N/A (without turbo) of that era were rated at 130 HP and with turbo, ranged between 160 an 185 HP.

Great engine and with proper care they run forever!!

Good Luck
Larry B

Edelweiss said:

Also the 120 HP rating you're quoting for a T or HT 6.354M is pretty low. The 6.354M N/A (without turbo) of that era were rated at 130 HP and with turbo, ranged between 160 an 185 HP.

Great engine and with proper care they run forever!!

Good Luck
Larry B

Click to expand...

Agreed!! Turbo 6.354 can go up to 240 HP on the Range 4s. 120 HP sounds very low to me for a 6.354.

First thing I'd do is crosscheck the temps on the FB gages. Do they match? If not, maybe a gage problem. If they do at 120, it might be the temp sensor/sender.

Then I'd check the temp with an IR Temp gun. Every boat should have one and they can be bought for about $25 at Harbor Freight. Check the two engines at the same points and don't forget to check the exhaust water temps. If the engines are operating at comparable temps with the IR gun, then you only have an indication problem. Swap the temp sensors and see if the problem follows the temp sensor.

If the engine is truly running that cool, then I'd chase the other paths suggested here. Don't start throwing parts at it until you now which parts are most suspect. Take a measured, reasoned, logical approach to tracking down the indication issue.

My Perkins 1984 6.354 4M is non-turbo rated 124 shaft hp @2800 rpm for recreational vessels. My temp gauges read low compared to handheld IR temps on the same metal as the sensor is threaded.

If voltage from alternators are different then you would also see differences in guage readings. Infrared cks will get your answer.

What is the engine serial number that is running cold?

Need help with parts for my Perkins T6-354

Hi to all Perkins fans

I have twins in my boat and serious trouble with the starboard engine.

The serial # is T6-354 UX 117951T.

The "X" denotes counter-rotation and apparently, it has different pistons

from the clockwise rotating port engine.

We can't get "1" replacement piston for it.

Can anyone in Perkins Land help locate said mystery piston ?
New or Used would be great.

Much Appreciated

Capt Nemo

Captain Nemo
These guys provided a set of obsolete Pistons for a Ford 192 recently. Maybe they can help. http://millsmotorparts.com


1983 Present 42 Sundeck
Twin Lehman 135's

The reason I asked the serial number for the cold running engine is that IF it is the contra-rotating engine and IF someone replaced the coolant water pump with one for the regular rotation engine, then it may overheat if a thermostat is installed....the backwards facing impeller fins may not be able to push coolant properly hence the need to remove the T stat.

I went thru this with a Chevy based gas engine several years back.

Try Trans Atlantic Diesel for that piston. I've bought lots of Perkins parts from them and they are very knowledgeable about these older Perkins. I agree with the other posters, 120hp is correct for a non-turbo 6-354

Not sure I understand why the piston would be different for a backwards rotation engine. I would challenge that for sure.

jleonard said:

Not sure I understand why the piston would be different for a backwards rotation engine. I would challenge that for sure.

Click to expand...

I suspect the issue is he wants to replace only one piston instead of all 6.

If you got to tear down an old engine to replace one piston, why not do them all?

Donsan said:

I suspect the issue is he wants to replace only one piston instead of all 6.

If you got to tear down an old engine to replace one piston, why not do them all?

Click to expand...

Not necessarily a need to replace them all if only one is damaged.

Another line of thought....after checking thermostats, pump, and water flow, you may want to look at the fuel system. You mentioned that performance was off on one engine. An engine that is running rich will run cooler. It should be simple to check. Is one engine smoking more than the other?

Or it may be as simple as it was for me on my T6-354 the thermostat was not sealing arond it self in the housing. Opened up and installed a small o-ring to seal properly and after that engine keeps correct temp regardles of load!

Lollipop said:

An engine that is running rich will run cooler.

Click to expand...

This is completely backwards. Diesels don't operate like gassers in regards to rich vs lean and the heat produced. Not calling Lollipop out, just want to let folks know when diagnosing their engine.
Also black smoke is an indication of running too rich. This can be due to too high pump tuning, washed out injector, bad or mismatched turbo, or plugged air intake. When it comes to turbos, bigger is NOT better. If not reasonably proportioned to the engine's displacement:rpm and fuel tune it won't spool properly and can result in damagingly high EGTS.

Sorry for the hi-jack, just trying to help folks understand their engine a bit more.

Back to the cooler running engine...My guess is that the thermostat has failed. Most diesel thermostats have a fail safe and when they fail it's in the open position...consequently, a cooler running engine...and just to let you know, diesel engines prefer to run a little warmer than 120 deg. Anyway, that's the first thing I'd do, swap out that thermostat.