Acceptable engine water temp at 5knots

jviss · Jul 24, 2013

mmeechan said:
I have a question I've searched for but while I found a bunch of interesting articles I didn't find the answer to my question.

I have a 1988 Catalina 27 with a Universal 18 engine.
When motoring at 4 knots or less the engine runs at around 1700 RPMs and has an engine temp of about 160F
If I push the engine up to 5.5 knots the engine water temp goes up to 180F

I'm wondering what is "acceptable" for that speed and engine temp. Since it usually sits at 160F I was wondering if 180 at that speed was ok. Honestly I may not have even noticed, but I just replaced my water heater and was concerned that I might get an airlock that I had read about in some threads. But since it isn't overheating and the temp stabilizes I think that is ok.

Thanks for any comments
Mike

What's the temperature of the thermostat? My understanding is that the engine should warm up to the thermostat setting, and then regulate at that point. I'm no diesel expert but 160º F seems a bit cool to me.

jviss · Jul 24, 2013

I see; I tried to find a spec online but no luck so far, but I did find the spec for your engine and it says operating temp is 165º to 195º F. So, I guess not to worry!

http://www.marinedieseldirect.com/universal/200157/universal-owners-manual-m-18-specifications.html

Alan Gomes · Jul 24, 2013

mmeechan said:
I have a question I've searched for but while I found a bunch of interesting articles I didn't find the answer to my question.

I have a 1988 Catalina 27 with a Universal 18 engine.
When motoring at 4 knots or less the engine runs at around 1700 RPMs and has an engine temp of about 160F
If I push the engine up to 5.5 knots the engine water temp goes up to 180F

I'm wondering what is "acceptable" for that speed and engine temp. Since it usually sits at 160F I was wondering if 180 at that speed was ok. Honestly I may not have even noticed, but I just replaced my water heater and was concerned that I might get an airlock that I had read about in some threads. But since it isn't overheating and the temp stabilizes I think that is ok.

Thanks for any comments
Mike

The thermostat for that engine is 160 or 165. They don't run it higher to avoid having salt precipitate out and clog the heat exchanger.

Once warmed up, the temperature should sit at the thermostat temperature (i.e., 160 or 165 as the case may be) and should * not* increase with additional engine RPM. That is not normal. You probably have some kind of partial blockage in your cooling circuit--quite possibly in the heat exchanger. If you have a 2" heat exchanger you might find that the cooling it provides is marginal, such that if there is even a slight amount of restriction you'll get the issue you are describing. Upgrading to a 3" diameter exchanger will give you some reserve capacity and eliminate this problem--again, assuming that is what is happening here.

jviss · Jul 24, 2013

Alan Gomes said:
They don't run it higher to avoid having salt precipitate out and clog the heat exchanger.

Gee, I've never heard of that, and I can't imagine how it would happen. I think I'm running a 170º thermostat in my M25, but even so I would imagine being able to go even higher than that. Unless you were actually boiling the water in the exchanger I can't see how this would happen. Note that seawater has a higher boiling temperature than fresh water, too.

Can you please elaborate?

jviss · Jul 24, 2013

more...

Just found this, wherein it is stated:

"Therefore, the raw water should never be heated anywhere near its salt precipitation point as it passes through a heat exchanger."

http://www.oceannavigator.com/October-2005/Saltwater-cooling-and-clogging/

Precipitation a concern with raw-water cooled engines, not in heat exchangers.

I'm interested to hear more on this topic, though.

Alan Gomes · Jul 24, 2013

jviss said:
Gee, I've never heard of that, and I can't imagine how it would happen. I think I'm running a 170º thermostat in my M25, but even so I would imagine being able to go even higher than that. Unless you were actually boiling the water in the exchanger I can't see how this would happen. Note that seawater has a higher boiling temperature than fresh water, too.

Can you please elaborate?

I'm no expert but here is the way I understand it:

The salt begins to preciptate out of solution at around 145 degrees or thereabouts. This is why raw water cooled engines have thermostats at about 140 degrees or less.

With a heat exchanger the engine can be run at a hotter temperature since the raw water flowing through it is not heated up as much as it would be running through a raw water cooled engine.

Actually, it might be that the Universal diesel, being fresh water cooled, could get away with a hotter thermostat--perhaps up to 190-deg. or so. Typically, though, the thermostat specified for this engine is 160. I've owned both the M-18 and the M25XP on previous boats and that was true for both of them, according to the Universal documentation, and that was what was in both of my engines.

As to the original query of this thread: whatever the thermostat, the engine should *not* be getting hotter with additional RPM, assuming it has adequate cooling capacity. If there is no restriction then the engine should run at the thermostat temperature regardless of whether the engine is run flat out or at partial throttle. I mentioned the issue of the 2" exchanger becuase this is a commonly cited problem with the Universal engines as they came equipped from Catalina. On the Catalina 30 forum the topic has come up a number of times and more than a few of the folks on there have upgraded to a 3" exchanger and eliminated this problem. Also, a quick Google search brought up this hit, which pretty well fills in the details: http://realitycheck.me/motoring-without-overheating-the-heat-exchanger-upgrade.htm

Also, Westerbeke has issued a bulletin on exactly this subject: http://realitycheck.me/docs/Universal_service_bulletin_195_heat_exchanger.pdf

jviss · Jul 24, 2013

Alan Gomes said:
whatever the thermostat, the engine should *not* be getting hotter with additional RPM, assuming it has adequate cooling capacity. If there is no restriction then the engine should run at the thermostat temperature regardless of whether the engine is run flat out or at partial throttle.

I completely agree with this. In fact, one wants it to heat up to thermostat temp where it will run more efficiently, I think.

Unfortunately, in most of these installations there's not enough cooling capacity, because of 2" heat exchangers, or inadequate raw water pumps or plumbing, and so forth. But at 2,000 rpm or so you should be fine.

jviss · Jul 24, 2013

Is it full of coolant? Do you have a coolant recovery tank?

jviss · Jul 25, 2013

mmeechan said:
I'm not sure if there is a recovery tank. I'll have to check that.
I believe it may be a little low on coolant. Perhaps 1/2 a cup to a cup based on what spilt out when I replaced the water heater.

I'm a little confused about that. Did you pre-fill the water heater coil with coolant when you replaced it? The coolant side capacity of a water heater is probably a lot more than a 1/2 cup.

Donnybrook · Jul 25, 2013

My M-18 does the exact same thing. Don't worry about it unless it goes above 195.

jviss · Jul 25, 2013

mmeechan said:
I'll be honest, I do lots of DIY stuff around the house, cottage etc, so I'm trying to delve into this new area called "the boat", but I'm basing the amount of coolant lost based on what came out when I made the swap and came out of the old HW unit when I tipped it back and forth to "empty it". I'll check levels tomorrow, but I didn't have any coolant when I did the switch, but I also didn't think I lost much in the swap. Perhaps I was wrong.
I appreciate the advice and comments

Mike

I think everyone has, at one time or another, had issues "burping" their marine diesel's cooling system; except the raw-water cooled guys. One method I've found virtually foolproof is to refill by pumping the coolant back in via the block drain petcock. I open the thermostat vent valve on top of the thermostat housing and pump it up. I think I may have loosened the thermostat housing bolts to let air bleed out of there, too, I don't remember.

Stu Jackson · Jul 25, 2013

Thermostats are either 160 or 180.

Burping: been discussed here many, many times.

Here's how to do it:

Engine Overheating 101 - How to Burp Your Engine (Reply #6) http://c34.org/bbs/index.php/topic,4518.msg26462.html#msg26462

jviss · Jul 25, 2013

Mine's 170º. That's what was in it, and that's the temp of the spare that was in the Universal parts kit that came with the boat.