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Old 11-08-2013, 11:48 AM   #41
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A diesel mechanic told me a long time ago one probably couldn't even fry an egg on the exhaust manifold of an idling diesel.

Which is why starting an engine during out of service periods does more damage than any possible good.
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Old 11-08-2013, 12:33 PM   #42
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Heat is a direct measurement of work being done as diesel engines are heat engines. Load is work. Work is heat. A diesel won't warm up w/o a load.

I take it that your cute riddle "How long is a piece of string?" to mean a wide range of temps. Not so. The answer is ... very cool. Coolant temp at idle isn't an indication of work being done it's an indication of how the thermostat is working. Coolant w/o the thermostat could be as low as 100 degrees .. I don't know but it would be so low no one would consider their engine warmed up to operating temp w/o the thermostat. My whole point here is to point out that the coolant temp is largely a false indication of overall engine temp. A diesel mechanic told me a long time ago one probably couldn't even fry an egg on the exhaust manifold of an idling diesel.
And I will somewhat prove both of your points. On my Mainship, if I just warmed it up in the slip and then changed the oil, the oil was barely luke warm although the coolant temp was 180. So I got in the habit of changing oil after running the boat hard out on the "lake". Problem was, I had to idle about 5 minutes to get thru the no wake zone to my boat. The oil cooler on that boat must have been awesome because by the time I got in and shut it down the oil was....maaaaaybe.....100-110 degrees....warmer than luke warm but just barely. The bottom line is I could never really get it as hot as I wanted it to change it. I had fantasies of changing it out on the water right after shut down...hahaha....but that was inviting all kinds of bad juju. So that is the way it was.

So yes, Rick, it is a function of oil temp. And yes, Eric, coolant temp is not indicative of oil temp(or work being done).
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Old 11-08-2013, 12:40 PM   #43
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After running the engine for several hours, my engine-compartment temperature is around 80 degrees 16 hours later while the outdoor temperatures are in the 50s and 60s.
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Old 11-08-2013, 01:07 PM   #44
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Thank's John for the input. Re changing oil you could just stop somewhere and drop the hook and change it there. Of course you'd be in a pickle if you lost your drain plug but you (like me) probably don't have one. But being tied to the float could be considered an advantage,Haha. But the temps you posted are very revealing.

I also think combustion temp at the piston and valves is very low also. As evidenced by the frying egg idea the exhaust is in direct contact w the manifold so it must be very cool also. The pistons and valves are in fact in direct contact w flame but on a relative basis I suspect the flame at idle is very cool (relatively speaking). But flame is flame and I don't really know.

Here's an and very related interesting question. For an engine running normally, say at high cruise where does the heat come from? Friction or combustion heat? I'm guessing 70 - 80% combustion.

Have they ever talked about how hot/warm an engine is at idle on BoatDiesel?
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Old 11-08-2013, 01:22 PM   #45
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And yes I agree EGT and oil temp should be the yardstick of real engine temp.
I have neither data points to go on. I just go down to the boat every week or two at the most, warm things up and go for a ride if it's pleasant... Exercise the running gear if not.

I think many of you over think this whole thing. My engine room stays well above ambient temps even on the coldest of days. With the Espar running for a 15-20 minutes it's downright tropical in there. I like to keep things lubed and moving and the boat is fine with it. It warms up nicely on even the coldest of days.

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Oh and another thing what would the coolant temp be at idle w the thermostat removed?
Who would do that? And what would the purpose be?
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Old 11-08-2013, 01:42 PM   #46
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SS,
Re running w/o a thermostat it's actually a bad thing to do. From what I've read the velocity of coolant in the engine water jackets is more than just flow. The design is in concert w the thermostat operating normally. Too much coolant flow/velocity isx not desirable.

And yes I've done much the same as you and it seems to be fine. A lot of these discussions aren't about things we need to know but things we find interesting and places the endless questions lead.
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Old 11-08-2013, 02:03 PM   #47
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SS,
Re running w/o a thermostat it's actually a bad thing to do. From what I've read the velocity of coolant in the engine water jackets is more than just flow. The design is in concert w the thermostat operating normally. Too much coolant flow/velocity isx not desirable.

And yes I've done much the same as you and it seems to be fine. A lot of these discussions aren't about things we need to know but things we find interesting and places the endless questions lead.
In old school jet boats, we ran washers in place of thermostats. A closed thermostat would let sand settle in the block, but you needed something to slow the coolant flow enough to let it take heat out of the steel. You tried different sized holes until you got the results you wanted. No thermostat is bad, worse when your cooling system is fed by the jet pump. I don't know if washers could be a temporary fix, or a way to test the cooling system.
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Old 11-08-2013, 02:04 PM   #48
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Re running w/o a thermostat it's actually a bad thing to do.
I completely agree. Thermostats keep engines warm. They like to be warm.

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A lot of these discussions aren't about things we need to know but things we find interesting and places the endless questions lead.
I agree there as well. There's a certain sense of satisfaction from stopping by after work and firing up the smoke generators (no glow plugs here) and listening to the rattle while you slip the lines for a quick jaunt over to the pump out or past the fuel docks.
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Old 11-08-2013, 02:12 PM   #49
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In old school jet boats, we ran washers in place of thermostats.
We did the same in dragsters when I was a kid. Just aluminum washers to restrict flow. We used electric pumps as well to preserve that extra bit of power that a reciprocating pump used.
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Old 11-08-2013, 02:14 PM   #50
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We did the same in dragsters when I was a kid. Just aluminum washers to restrict flow. We used electric pumps as well to preserve that extra bit of power that a reciprocating pump used.
Yup, same here. Or block fill, run methanol and just cool the heads with a couple quarts and an oil cooler.
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Old 11-08-2013, 02:29 PM   #51
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Who would do that? And what would the purpose be?

More to the point, why even ask such a question?
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Old 11-08-2013, 02:48 PM   #52
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The point was obviously to determine how much heat was being generated by the engine and completely a theoretical exercise of the mind and discussion. You speak as though I suggested somebody do that ... Hardly.

One should dismiss the notion that one's engine is warmed up when the coolant temp is up because it says almost exactly the same thing running hard ..... developing much much more heat.
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Old 11-08-2013, 02:58 PM   #53
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Speaking theoretically then;

If an engine is running, it is generating heat. (check)

If there is excess heat it is radiated through the block, into the oil, out the exhaust and into the coolant. (check)

It takes a certain amount of excess heat to warm the coolant and a certain amount to keep it at that temp (check).

My boat tied to the dock at 1000 RPMs is under the same load as if it were cruising at that RPM. Assuming your fears are founded, we should never operate for extended periods at those RPMs because our blocks will cool and damage the bores.

But following that logic; If I'm holding working coolant temp at a safe level, the oil will eventually get there as well. Yes?
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Old 11-08-2013, 03:13 PM   #54
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No because the oil isn't controlled by a thermostat. And you probably have a sizable oil cooler w flowing sea water in it.

And we don't cruise at 1000rpm.

And you said it ..... running slow will be too cool.

And I've lost most of my fears of under loading but I wouldn't do it unless I considered the engine disposable. Like I had a GB 32 and I was dy'in to repower it.
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Old 11-08-2013, 03:41 PM   #55
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the million dollar question is....too cool for what? My engine manuals never say don't run at 1/2 throttle or 3/4 or even 1/4.....they put a cooling system on that is designed to keep the temps reasonable and don't give a damn about anything but running with NO load...not a partial load.

So as long as my temps are up for a given amount of time every week...and the temps are going to vary with the load...I seriously doubt I am hurting anything.

Anyone thinks that's hurting an engine ought to tell mechanics troubleshooting an engine that they have to wait 30 minutes at 80% load every time they start the engine to test the starter, alternator or gauges....etc...

gimme a break....
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Old 11-08-2013, 04:32 PM   #56
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... gimme a break....


Someone must be having a bad day and needs to stir the pot for some reason. Too bad because that sort of voodoo engineering doesn't contribute much to the knowledge base that these forums are supposed to be for.

For those who are truly interested, maybe a reread of post #34 is in order.
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Old 11-08-2013, 07:13 PM   #57
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This was from warming my engines up today!!! A good IPA for a companion!
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Old 11-08-2013, 07:48 PM   #58
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Exercising one's engine(s) is a great excuse for going boating!

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Old 11-08-2013, 08:07 PM   #59
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Yes you're post 34 and John's post 32 have a lot in common.

It's interesting to observe that usually an engine's cooling system is controlled by keeping the engine hot enough and the lube oil system is controlled by a cooler to keep it from getting too hot. So the coolant is held artificially high and the lube oil is kept artificially low.

So if you took the thermostat out and the oil cooler you'd probably be able to tell a great deal about how hot or warm or cool or whatever. John would ideally do better by opening a valve to by-pass the oil cooler unless running the engine moderate to hard. I've often thought it may be good for all or most of the underloaders here to by-pass their oil cooler. Oil temp should probably be well within limits but considerably warmer than w the oil cooler hooked up while their running the Lehman's 14 to 1600rpm. Would need to be placarded of course.
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Old 11-08-2013, 09:04 PM   #60
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Lehmans run just fine at low rpms...forever....why make life more difficult with extra valves, etc.... when no one has shown where running a Lehman at 1600 rpm for 20000 hours is detrimental.

I keep wondering how we get into these "the sky is falling threads"????
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