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Old 12-07-2013, 14:53   #1
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Running with no Thermostat in 4-108

My very recently restored 4-108 is running hot at above 2100 rpm. I have the prop pitched to run up to 3,000 rpm in gear but gets up to 210 deg after awhile over 2,100rpm. Heat exchanger was descaled and exhaust elbow changed out during recon. I would like to test it without a thermostat. Is this adviseable? Engine used to run at 170/180 before recon and re pitch (max rpm used to be 2,400). It has a new perkins thermostat .
Boat is 25,000lbs
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M
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Old 12-07-2013, 15:06   #2
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Re: Running with no thermostat in 4-108

Something happened during the "restoration".

Your prop pitch change (from 2400 max RPM to 3000 max RPM) should have put LESS stress on the engine, not more.

"Descaling" is often not very effective.

As I and others have noted many times, the 4-108 heat exchanger is undersized.

Nevertheless, it's not a good idea to run without a thermostat.

If there's no major blockages in the water jackets, if the water pumps (raw water and internal circulation) are fitted and working OK, if you have the proper 50/50 coolant mix, and if the stock 4-108 heat exchanger is truly clean then the engine shouldn't overheat even running near max RPMs.

After fixing everything else on my 4-108, I put on a larger (Perkins 4-154) heat exchanger some 13-14 years ago and haven't had cooling problems since.

Bill

PS....check to be sure they didn't mix up the gaskets on the circulation pump....the one behind the steel plate is NOT identical to the one in front. If you mix these up, the engine won't circulate cooling water properly.
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Old 12-07-2013, 15:16   #3
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Re: Running with no thermostat in 4-108

Of course you should try it without but it shouldn't make a difference.
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Old 12-07-2013, 15:23   #4
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Re: Running with no thermostat in 4-108

If you're really curious about the operation of the thermostat, put it in a pan of water and heat the water to boiling.

Note when the thermostat opens.
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Old 12-07-2013, 23:51   #5
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Re: Running with no thermostat in 4-108

As John A says. Check out your new thermostat. What he didn't say is check the temperature at the point that it opens. It should open well before boiling.
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Old 13-07-2013, 00:04   #6
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Re: Running with no thermostat in 4-108

I prop and tranny my perkins to run at 1800 to 1850 rpms and never heard of running them the way folks are doing these days ! Ive never had heating problems, or stuff like that ! I was taught and had paper work that told me to stay at 1800 rpms for long life on a perkins 4-108 so I can'thelp ya out, except slow it down ! My perkins have went way over 8000 hours ! so im just makeing a suggestion!
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Old 13-07-2013, 01:08   #7
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Re: Running with no thermostat in 4-108

All engines manufacturers impose limits on there own engines, in this case Exhaust temp, Jacket water Temp, Oil Temp, Revs. One of these you will hit first then you must not exceed.
The load on the Engine is strictly determined by the propellor Law, it is altered by weather/sail contribution, fouling of the hull/propellor and changing the prop.
If you under prop the Engine load will diminish the temperatures will come down. If you over prop (This is not silly, ships do it intentionally) you will reach your maximum Temps earlier.
You haven’t mentioned if the vessel is motoring faster or slower but if something is happening that is outside these guide lines there is a “stuff up” somewhere.

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Old 13-07-2013, 02:31   #8
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Re: Running with no thermostat in 4-108

What the Johns say: I've had a brand new thermostat DOA and totally inoperative. Put it on the stove, see that it really opens. Marine raw water thermostats usually are not plumbed the same way that cars and closed coolant systems are. If it is raw water, the thermostat acts like a diverter valve. If it stays closed, the water never enters the engine, it just gets pumped out the exhaust. When it opens, the water is shunted through the engine block instead of the dump path, so the thermostat is acting like a "y" valve. With no thermostat, It is hard to tell where how much water will go.
If the thermostat opens on the stove, and it hasn't been installed backwards (don't ask me how I know that), or the gasket hasn't somehow blocked the passage, then it won't be the problem. But I'll never trust an untested thermostat out of the box again.
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Old 15-07-2013, 11:51   #9
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Re: Running with no thermostat in 4-108

Thanks for the replies.
This weekend I installed a new and working 160 deg thermostat. I checked the raw water strainer and made sure there was no air lock in coolant and heater.
I ran the engine in gear at the dock and checked tempeture with a heat gun sensor.
2,500 rpm read 210 at the metal fitting going into the heat exchanger and 180 going out. Which gives me a 30 deg difference.
The next day I went out for a motor on fairly flat water and got
2,000 rpm 180 deg and 4.5 knts
2,500 rpm 210 deg and 6 knts
3,000 rpm 225 deg and 7.3 knts

My questions are
a) Should I increase pitch to reduce rpms and would that cause the engine to run cooler?
b) Change out to a larger heat exchanger and would that cool the engine down more than 30 degs? And which exchanger?

At 2,500 rpm the engine sounds goood with no steam or smoke.
Many thanks
Mark
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Old 15-07-2013, 12:04   #10
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Re: Running with no thermostat in 4-108

Is there any suspicion that your heat gage or sender or heat gun could be calibrated improperly? That sounds really very high.

kind regards,
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Old 15-07-2013, 12:11   #11
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Re: Running with no thermostat in 4-108

Checked it against a meat thermometer which is not testing lab accurate but all I had.
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Old 15-07-2013, 12:33   #12
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Re: Running with no thermostat in 4-108

Quote:
Originally Posted by Wainui View Post
Thanks for the replies.
This weekend I installed a new and working 160 deg thermostat. I checked the raw water strainer and made sure there was no air lock in coolant and heater.
I ran the engine in gear at the dock and checked tempeture with a heat gun sensor.
2,500 rpm read 210 at the metal fitting going into the heat exchanger and 180 going out. Which gives me a 30 deg difference.
The next day I went out for a motor on fairly flat water and got
2,000 rpm 180 deg and 4.5 knts
2,500 rpm 210 deg and 6 knts
3,000 rpm 225 deg and 7.3 knts

My questions are
a) Should I increase pitch to reduce rpms and would that cause the engine to run cooler?
b) Change out to a larger heat exchanger and would that cool the engine down more than 30 degs? And which exchanger?

At 2,500 rpm the engine sounds goood with no steam or smoke.
Many thanks
Mark
a) No.
b) Not necessarily. Something else is wrong. 210F @ 2,500RPM is too high.

The Perkins 4-108 is meant to run at 180-190F with fresh-water cooling. The 160 degree thermostat is for use with raw water cooling, because at higher temps salt precipitates inside the engine water jackets.

I can run my 4-108 at 2,500 RPM all day long without overheating. Of course I do have an oversize (4-154) heat exchanger, but even with a new stock 4-108 heat exchanger and other things fixed I could and did run wide open in the tropics for several hours without overheating. The expert mechanic I'd flown in from the States asked me to do this, after he'd performed his magic and found several things wrong with the engine and corrected them. (The test run was successful, so we just went sailing and enjoyed ourselves :-)

Did you check the gaskets on the fresh water pump plate, or ask the mechanic who "rebuilt" the engine about them?

Bill
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Old 15-07-2013, 12:38   #13
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Re: Running with no thermostat in 4-108

Wainui-
Easy way to check the heat gun. Boil a pot of water. You're at sea level, so it will be 100C or 212F when it is on a rolling boil. Handy calibration source, which can be turned into a nice cuppa afterwards.

Before you swap out the heat exchanger, is that something a PO simply bolted up? Or something the manufacturer might have carefully spec'd?

Since the change comes after a reconditioning (which if anything should make it run cooler, rashly assuming no blockages, etc.) and a prop change resulting in a major RPM change...I'm not sure the RPM change per se would make any difference. Putting a higher load on the engine, more RPM with the same or more pitch, would increase the load and might create more engine heat, creating the need for more cooling. That would sound logical.
It might be worth researching what counts as "too hot" for the 4-108, offhand I have no idea.
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Old 15-07-2013, 13:53   #14
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Re: Running with no thermostat in 4-108

I had an overheating problem with my Perkins 4-108. What I finally did was verify that I was receiving a good flow of fresh water to the impeller pump.
L disconnected the hose from the seacock and discovered that barnacles had grown inside the seacock between the screen and the valve. Once they were removed my overheating problem was cured.
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Old 15-07-2013, 18:06   #15
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Re: Running with no thermostat in 4-108

So as per John A you could have problems with the SW circuit. If sea growth, you could try putting a cup full Chlorine in the sea suction filter leave it for a day, if something does loosen the sea suction filter will catch it, it may indicate mechanical cleaning is req'd. Sounds like you have a penchant for speed, heat = K*power and if your heat exchanger is undersized, it may already have salt scale, very bad for cooling but won't effect SW flow, think about 40-50Deg C is maximum temp of SW before you get salt scale.
Changing to a courser prop, would make any deficiency on SW side exacerbated. Did you ever measure SW flow at the exhaust to compare now.?
Make sure that temp gun is reading right, if you got the temperatures you say, I would think it'll be blistering hot near the engine, do not exceed manufacturers recommendation on RPM.
Why would you consider a) proposal when you have so many problems already, reducing revs as per propeller law would help, heat=K*power.

Oceanrider Once I thought I was a big ship Marine Engineer
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