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Old 16-04-2015, 11:36   #1
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Engine Temperture

I'm running a Perkins 4-108 (original) in a Cooper 37. From talking to the previous owner, the engine has "always "run a little hot. He's looked at the intake, strainer, pumps, and manifolds. The engine gauges are original (1983?) and typical, (lacking calibration). It occurred to me that the engine temp gauge might need calibration, so I took the cooling cap off, ran the engine to operating temp and inserted a digital temp probe. It read about 10 degrees lower that the gauge.
My question is .. Is my deduction sound, or is there a better way to double check engine running temp?
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Old 16-04-2015, 11:47   #2
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Re: Engine Temperture

You might get a more accurate reading by investing about $25 in a digital thermometer and "shooting" the block, the exhaust manifold and coolant tank. My 4.108 operating temp is approx. 185' at 1800-2000 rpm. If I push it above that, the temp climbs. Bob
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Old 16-04-2015, 12:35   #3
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Re: Engine Temperture

The previous post is referring to an infrared tenperature gun that you can point at the head, the fresh water pump, etc. Best way to check operating temps.
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Old 16-04-2015, 12:44   #4
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Re: Engine Temperture

My 4-108 in a heavy 44 footer with a MaxProp pitched for about 2800 max rpm ran on the cold side if anything. I've read that there were two types of cooling systems on the 4-108, and the cooling of one is marginal. Maybe that is your issue? I think mine was a Bowman system, but not sure at this point.
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Old 16-04-2015, 12:45   #5
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Re: Engine Temperture

Quote:
Originally Posted by roberttigar View Post
You might get a more accurate reading by investing about $25 in a digital thermometer and "shooting" the block, the exhaust manifold and coolant tank. My 4.108 operating temp is approx. 185' at 1800-2000 rpm. If I push it above that, the temp climbs. Bob
I thought he said he was using a digital thermometer??
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Old 16-04-2015, 13:51   #6
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Re: Engine Temperture

4108 here. 37ft sailboat, 20k lbs. Normally run at 1700 rpm. Engine temp around 180 to 190. The standard heat exchanger on some (mine) is undersized in my opinion, and there is a larger one that can be retrofitted.

Two years ago I decided to replace my 30 year old stewart warner guages with all new stewart warner guages. I was on the hard so didnt get to run the engine for a few months. When I did the water temp guage shot up to 220. Couldnt find any problems so I asked my excellent mechanic to look it over. He brought his digital temp guage. Shot it all over and couldnt find any problems.

I mentioned to him that I had changed out all the guages. He asked me if I also changed out the sensors.

No, I hadnt. Bought myself a digital temp gun that day....
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Old 16-04-2015, 14:14   #7
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Re: Engine Temperture

25,000lbs boat with 17" max prop P4-108
can run up to 3,000 rpm in gear
@ 2,600 rpm 6knts 180 deg
@ 2,800 rpm 6.5knts 190 deg
has separate HE.
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Old 16-04-2015, 17:22   #8
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Re: Engine Temperture

Yes, you have found the correct area.
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Old 16-04-2015, 18:13   #9
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Re: Engine Temperture

Quote:
Originally Posted by Cheechako View Post
I thought he said he was using a digital thermometer??
No he said he used a digital probe in the coolant tank not an infrared thermometer gun.
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Old 17-04-2015, 10:11   #10
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Re: Engine Temperture

Thanks all for your reply. I did use a digital gauge, but not the type you "aim" at the engine. I used an immersion gauge into the coolant
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Old 17-04-2015, 13:47   #11
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Re: Engine Temperture

The 4-108 in my opinion is one of the very best engines ever marinized. Through all my discussions with other 4-108 aficienados is that the cooling problems are usually associated with over propping, clogged mixing elbows in the exhaust, scaled up tubes in the exchanger or water intakes and pumps. Sometimes water pumps won't push water to the max because of plate wear and not just because the impeller is old. If you check all of those one at a time starting at the very intake end of the system and working toward the very end of your exhaust and check to see if your prop is not too large or have too high of pitch then you should be able to track down the source of high temps. I hardly ever used my engine above 2000 rpms so never got it to overheat.

You said the owner looked at all the stuff but how closely did he look and did he take things apart?
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Old 17-04-2015, 14:36   #12
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Re: Engine Temperture

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Originally Posted by SkiprJohn View Post
The 4-108 in my opinion is one of the very best engines ever marinized.
Maybe even the BEST engine ever marinized. And yes I take very good care of it including and especially the entire cooling system. And I run at 1700, never been over 2000. I've never overheated.

But I still think the exchanger could be bigger, and apparently so did perkins when they changed from the small stand alone unit to the larger integrated unit. But I prefer the standalone because its simpler and easier to service.
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Old 17-04-2015, 15:11   #13
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Re: Engine Temperture

I agree the original was too small. My 1980-vintage 4-108 was giving me fits in the Caribbean with overheating, before I changed out the heat exchanger.

I fitted a larger one (I think for a Perkins 4-236) which fit OK with just a little engineering.

NO problems since (that was some 15 years ago).

My engine runs at 2200-2300RPM cruising (28,000 lb 42' sloop with 3-blade 17" MaxProp).

Even if I push the RPMs higher, the temp remains between 180F and 190F where it should.

Bill
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Old 17-04-2015, 15:42   #14
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Re: Engine Temperture

I have a 4.108 in a 22,000 lb ketch with a 3 blade max prop. I thought that it was running hot so I had the heat exchanger cleaned out by a radiator shop. Still running above 190 so I borrowed on IR thermometer and got a reading at the heat sensor of 150. Replaced the Stewart Warner temp gauge and now shows 180 at 2800RPM. Make sure the heat exchanger has good flow but don't trust the guage.
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Old 17-04-2015, 17:32   #15
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Re: Engine Temperture

What boat speed are you getting at about 2,600 rpm with you 3 blade prop?
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