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Old 06-28-2013, 09:11 PM   #1
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Diesel engine temp?

Our first run with engine back together today. We learned a few things. Engine ran nice, temp seemed to be at 185 most of time then dropped to 175. Does that sound to cool for a 1969 Ford Lehman Diesel 120? Other issue; we have a pipe connecting rocker cover to manifold. Manual calls for a emission control valve. Is that thing necessary and what is its function?
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Old 06-28-2013, 11:18 PM   #2
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In Summer my Lehman runs about 90C, and in winter with cooler raw water at about 85-87C. The thermostat control is not that fussy. I'll leave you to do the deg F conversion...the price you in the US can pay for not adopting Systeme Internationale.
As to the emission control valve, etc, when I got sick of mucking round with an oily bit of foam rubber around the original air cleaner, (so called), I went over to a pod type air filter, and just left the former unconnected. Others may differ, but I did not feel the tiny difference in emissions from connecting the rocker cover vent through the air filter justified trying to hack into the new pod filter not designed to accommodate it. However, in your case it appears the rocker vent goes straight into the exhaust manifold. (Unless that is a strange long flat air cleaner hard against the exhaust manifold). If it does go into the exhaust manifold I would think in that case a check valve only allowing flow from rocker to manifold would make sense, or otherwise in some instances gases could be forced back into the rocker, and this set-up is not good, and may explain why my 1975era engine had this rocker cover vent go through the air intake, so it was recycled rather than extracted through the exhaust.

If I am being fooled by appearances, and the vent is going into the air intake/filter, then the valve would not be so critical, but mine does have a rudimentary valve in the line, so it might be as well to obtain one from American Diesel. There usually is a reason for everything, and it's function might be to limit suction effect as well as back flow. As to where the end of the vent goes after the valve..less important really from an emissions point of view when in the engine room of an old boat in my view.
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Old 06-29-2013, 12:12 AM   #3
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Thanks much Peter, I'll do the conversion
Appreciate the response and advise.
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Old 06-29-2013, 11:19 AM   #4
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Just a thought here on temps.

Most here on TF seem to run their engines very slow and as a result under loaded. And hence very cool. And most here (I think) do believe that under loading is "probably" not a serious problem but I think most agree it's better to run at 50 to 70% load to keep operating temps up where they should be.

Some of the downside of under loading could probably be compensated for by running the coolant on the warm side. I run mine 190 but it's a fairly new engine. The Lehman's have that cooling problem on the back cylinder so running 190 may not be an option .... at least a recommendable option. If I had a Lehman I'd be drawn both ways on this issue.
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Old 06-30-2013, 02:35 PM   #5
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I will say, it is nice to have a successful engine recovery after this experience. We even tried setting the valve adjustment after warming up the engine. That worked well, at least the engine sounded smooth after the adjustment. It was necessary since we mixed up the push rods. On our sea trial we ran from La Conner up to Anacortes and back. Twice did a stress test at full throttle, as Bob Smith recommended, and she purred along nicely. Throttle was limited at 2,200 rpm which we held for 60 seconds each time.

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Old 06-30-2013, 03:12 PM   #6
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THat sounds like your thermostat is working normally, in that, it's letting the engine warm quickly and then fully opening to operating temp.
in My Lehman 135, running temp is 172F at 1600 to 1700 rpms.
If I push the engine to around 2000 rpms, temp increases to about 182

I've never seen it above 185

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Old 06-30-2013, 03:47 PM   #7
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Wxx3,

I think the thermostat only opens fully during extreme conditions. "operating" load is so low on most trawlers that the thermostat probably only opens a little. If it opened fully at a 40% load and the temp was 170 what would the engine do for a cooling system at full load?
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Old 06-30-2013, 05:54 PM   #8
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Quote:
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Wxx3,

I think the thermostat only opens fully during extreme conditions. "operating" load is so low on most trawlers that the thermostat probably only opens a little. If it opened fully at a 40% load and the temp was 170 what would the engine do for a cooling system at full load?
Then I don't understand the function of the thermostat.

It's there to get the engine up to operating temperature and keep in there in conditions when it would run colder. It can't do anything for an overheating engine.



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Old 06-30-2013, 06:40 PM   #9
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Then I don't understand the function of the thermostat.

It's there to get the engine up to operating temperature and keep in there in conditions when it would run colder. It can't do anything for an overheating engine.



Richard
I agree...

so does this and every other site I visited...

HowStuffWorks "How Car Cooling Systems Work"
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Old 06-30-2013, 07:35 PM   #10
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You're "HowStuffWorks" link is written for average people and is greatly simplified. You will notice when you re read it that the thermostat is not fully open at 195 degrees. They only say the thermostat is fully open at 200 degrees. The thermostat only allows enough cooler water to enter the engine to keep it from getting too hot.

If it opened fully on a light load the engine would run too cool. The thermostat reduces the cooling capability of the engine at all times except under maximum load. Then the thermostat opens fully. The cooling system is matched to the engine so that the capability of the cooling system with the thermostat fully open the engine will run at the predetermined safe operating temperature and as the load decreases the thermostat closes just enough to maintain the operating temperature.

So most all the time the thermostat is NOT open fully.
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Old 06-30-2013, 08:06 PM   #11
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I know...but the upper range of normal operating temps is't necessarily "extreme conditions" as you state....just at the range of the upper temp range as determined by the thermostat.

When the system is at the upper range of operating temp and the thermostat is fully open and there is too much heat....the engine overheats...seems pretty simple to me.

Or just like when some people remove the thermostat and the system still overheats....doesn't have to be extreme conditions...
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Old 06-30-2013, 11:40 PM   #12
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An engine operating at maximum prescribed temperature limit is operating at the extremity of a range. It follows an engine operating at that point is in "extreme" operating conditions, for temperature purposes.
Maybe not if you just want to generalize, but we are talking about "Diesel Engine Temp" here.
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Old 07-01-2013, 01:49 AM   #13
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WOT is certainly considered extreme by most here. Many are even afraid to go there.

When the thermostat is wide open that's wide open throttle for the cooling system. If the cooling system is wide open (doing all the cooling it can) at light loads then w more load applied the engine couldn't do anything but overheat.

So the thermostat can't be fully open at light loading.
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Old 07-01-2013, 08:51 AM   #14
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Quote:
Originally Posted by Wxx3 View Post
THat sounds like your thermostat is working normally, in that, it's letting the engine warm quickly and then fully opening to operating temp.
in My Lehman 135, running temp is 172F at 1600 to 1700 rpms.
If I push the engine to around 2000 rpms, temp increases to about 182

I've never seen it above 185

Richard
The book for the SP135 says the thermostat (should) begin to open at 157-164F and is fully opened at 186F. It look like your engine is cooling as it should.
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Old 07-01-2013, 01:24 PM   #15
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it should be so easy

Quote:
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The book for the SP135 says the thermostat (should) begin to open at 157-164F and is fully opened at 186F. It look like your engine is cooling as it should.
And I may add that between the $1 (if that high) piece of bi-metal in the thermostat to make that happen and your temperature instrument with wire run and everything else, that we are lucky if these numbers are +/- 10F.

In my early days, when I had too much time and a Bunsen burner, I found that the range of an opening thermostat varied by at least 10 AND there was a very small range between just opening and fully open.

We must all keep in mind that it is a very long, circuitous trail from the brain of the white coated engineer who designed this piece to the bean counters who then reduced its cost to manufacture, and finally the little Chinese household where this had been farmed to actually make.
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Old 07-01-2013, 01:30 PM   #16
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Oh I forgot

the whole issue of standard deviation and what that raelly means in the manufacturing process
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Old 07-01-2013, 03:15 PM   #17
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I agree generally w everybody except that I don't think the thermostat does open fully in an engine while it's running. It may in an engine with a marginal cooling system or one plugged up. But not w a good system.

Let's say we make the observation that our well maintained Lehman runs at 180 degrees normally at about 1600rpm.

Now take the thermostat out.
If the thermostat was all the way open ther'e would be no change in temp at 1600rpm. BUT I'm positive it's going to be WAY lower ...... Because the thermostat was not fully open.

And Wxx3 there would be the variation in the temp gauge to add to the thermocouple in the thermostat.
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Old 07-01-2013, 06:46 PM   #18
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I agree generally w everybody except that I don't think the thermostat does open fully in an engine while it's running. It may in an engine with a marginal cooling system or one plugged up. But not w a good system.

Let's say we make the observation that our well maintained Lehman runs at 180 degrees normally at about 1600rpm.

Now take the thermostat out.
If the thermostat was all the way open ther'e would be no change in temp at 1600rpm. BUT I'm positive it's going to be WAY lower ...... Because the thermostat was not fully open.

And Wxx3 there would be the variation in the temp gauge to add to the thermocouple in the thermostat.
Eric,

I actually agree with you and I think we are saying the same thing though viewed differenly.

I was addressing the issue from the way Randall B had first mentioned it, " Engine ran nice, temp seemed to be at 185 most of time then dropped to 175. Does that sound to cool for a 1969 Ford Lehman Diesel 120?"

I was trying to address the issue of a mechanical thermostat will sometimes do exactly that, showing a spike in the temerpature, based on its delay in opening. And ussually that indicates that the engine is supposed to run at the lower (after opening) temperature.

And yes, totally agree that probalby my engine on cool day would run lower without thermostat.

Lasrly, I like 175 as a running temperature, as too many times in my experience, when engines ran warmer, even only 185, it was a sign of hot things to come
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Old 07-01-2013, 10:08 PM   #19
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And I may add that between the $1 (if that high) piece of bi-metal in the thermostat to make that happen and your temperature instrument with wire run and everything else, that we are lucky if these numbers are +/- 10F.

In my early days, when I had too much time and a Bunsen burner, I found that the range of an opening thermostat varied by at least 10 AND there was a very small range between just opening and fully open.

We must all keep in mind that it is a very long, circuitous trail from the brain of the white coated engineer who designed this piece to the bean counters who then reduced its cost to manufacture, and finally the little Chinese household where this had been farmed to actually make.
Pessimistic much?

Bi-metallic? You sure about that? Most are wax thermal motors and are quite accurate due to precision manufacturing. You can get an upgraded one that is even more accurate and non-linear with a v-notch weir in the disc. A good quality thermostat is actually made in the US or the EU as the nature of the wax is proprietary. I don't think I've ever seen a Chinese one.

I would argue that the often maligned poor little thermostat is only one of the issues with a cooling system. Fouled heat exchangers and the linearity of the positive displacement pump governed by engine rpm (think turn down capacity) have more to do with any perceived cooling issues.
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Old 07-01-2013, 10:31 PM   #20
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Yes Wxx3'

In view of the Lehman's overheating problems I'd opt to run 175 too. That's probably running by 1953 Plymouth standards but that's basically where it's at. In view of this it's hard to identify w rebuilding these engines as a lot or even most here don't get over half throttle but yuo'd need to disclose to the next owner you can't run it over half throttle .... I'd feel kinda silly telling one that but I'd feel ethically bound to or I'd even feel worse.

Yea I'd run the Lehman 175 but if it didn't have the cooling problem I'd run it 190. That's where I run my Mitsu per factory specs. The Mitsu's about an 05 engine but not very different than the Lehman except for thin-wall casting and probably some injection features. And probably some other features I don't know about.

And Randall I don't think cooling system surges in a healthy system is unusual. Especially for an old engine. It's like a thermal lifting off the ground and quickly rising to several thousand feet. Then the air cools off and cooler air moves in to replace the air that "popped" off as a thermal. You'd think all would average out and stabilize but the cycle just keeps going as long as the sum heats the ground.
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