Cold Water Operating Temps

[TyeeMan]

Good day everyone,
New to this forum, although I've been reading it for about a year, and now I have my first io. Let me first say many thanks to the people that contribute to this forum, it is truely a wealth of information, especially for the do it yourselfers.
My question is regarding engine operating temps in cold water. I have 1990 Lund Tyee with a 3.0L RWC, and a new SEI outdrive. I've owned this boat for approx. a year, before this boat I've owned outbaords. What happens is in cold water, 40 to 55 degrees, when I'm under way and the engine is at idle, my temp gage slowly gets up to 170 degrees and stays there. As soon as I increase engine speed the temp drops right down to 140 - 145 and stays there until I return to idle again. As the water temps warm into the 60s and up, the temp is much more stable, it might top out at 155 after troling for a while. I understand that "normal" operating temp for this engine is in the 140 deg area.
Is this normal for cold water operation? Looking at the way in which the water flows on the engine, it appears to me that perhaps the cold water that flows past the thermostat in the t-stat housing and into the exhaust manifold might be making the t-stat open a little later, until the water in the block gets warm enough to over come the cold water going to the manifold. Could this be possible? Aside from that, all functions are normal and might I say predictable.
I have insalled a new Merc 140 deg t-stat, I also took it back to the dealer and had them shorten the water supply hose as it looked to be kinked, no kinks any more. This boat has approx. 200 hours on it and has only been used in fresh water up here in Minnesota.
Any help on this would be greatly appreciated!! Thanks again everybody!

 

[Haut Medoc]

Re: Cold Water Operating Temps

Welcome to posting on iboats......
I think the temp should be more uniform....
You say you have a new drive so I would think that your impeller is OK.....
It does sound like you have a problem with water flow....
If you are not getting over 170* you have caught it in time......
When was the last time the risers were off & checked?
Especially at the 'dumps'....
Scale can clog the outlets & restrict water flow.....
It appears to me that you are not getting enough flow @ idle.....
The first thing to check would be the impeller....
Do you ever start it without a sufficient water flow or boat in muddy/sandy water?
In your case, I would check the risers first....
If thay are clean, check the impeller....
Third would be to test the therostat for proper operation, (even if new)..........JK

 

[TyeeMan]

Re: Cold Water Operating Temps

Being that I've only owned the boat for one year I really don't know when or if the riser has been off. If memory serves, the bolts on the risers give no evidence that they've been out.
Could you please explain the "dumps"?
I personally have never started the boat out of the water, that's not to say that the dealer did though. Incidentaly that dealer went out of business last summer, hmmm.
I just keep going back to the fact that in summer time lake water temps the engine temp is very stable. It's in the early or late season boating when the water temps drop into the 40s is when the engine temp really fluctuates, and again, it's only at idle or trolling speed.
I do know that the rubber connector (sorry don't know the correct name) between the down portion of the riser and the solid "pipe" where the flapper resides has been replaced. By the way, should the flapper valve rattle a little at idle or trolling speed?
Thanks,

 

[Haut Medoc]

Re: Cold Water Operating Temps

When you pull off the riser(elbow) there are two small holes(dumps) inside where the water from the engine is expelled.....
This is the only place water (coolant) gets out, if it is partially blocked it will interrupt flow.....

do know that the rubber connector (sorry don't know the correct name) between the down portion of the riser and the solid "pipe" where the flapper resides has been replaced.
Exhaust bellow

By the way, should the flapper valve rattle a little at idle or trolling speed?
They often do....
Another thing to check while the riser is off....
They are cheap to replace, btw....(flapper)

Again, 170* is not over heating, but a little warm....
Riser or impeller is my guess....
If you do not know the condition/age of the riser, it should be inspected....
If it fails, it will put water in your engine....
For the price of a gasket & undoing 4 bolts & 2 clamps it is well worth it, imho..........JK
Curious, does it get this warm on muffs?

 

[Bondo]

Re: Cold Water Operating Temps

impeller is my guess....

Me Too...........

If this is a freshwater run boat,.........
The Impeller is My 1st Guess.....

If it's a Saltwater boat,....... It could be Either 1...........

 

[ziggy]

Re: Cold Water Operating Temps

if the risers and manifold are 17 years old. i'd think i'd suspect them enough to inspect them at the very least if it was my boat. ya can check yer flappers then too. what these guys above have said seems to be the things to check. it seems that in any overheat condition the impeller is first suspect also. but a 1 year old drive that's never been started out of water just don't seem likely. least ya'd hope not. to me still would have to be suspect though.
in thinking about a t-stat. it 'starts to open at 140. and is full open at 160. so to me temp could vary inbetweenest them numbers and be ok. your only ten on the high side. ya say after throttelin up it drops to the 140-145 range. if 145. then ya'd only be 5 high, assumeing the gage is off by 5 on the high side. any chance the gage is not givein you the proper temp # but is deflecting proper? off by 5 or 10*. at least you've got numbers. my temp gage is in the green or in the red, no numbers.... just a thought on the gage....

out of couristy, why did yer boat with only 200 engine hrs get a new drive?

 

[TyeeMan]

Re: Cold Water Operating Temps

She runs just fine on the muffs, all kinds of water being expelled from the transom as well.
The boat has been run in nothing but fresh water.
The reason for the new drive is that the previouse owner used it most of the time on Lake of the Woods on the border of Canada and Minnesota. He hit one of the many hidden rocks. For those not familiar, Lake of the Woods is a large glacial shield body of water. Awsome fishing but pretty tuff on lower units and the like if one gets off course.
As for the gage, personally I tend to look at it as a point of reference as appose to a caibrated type gage. If the gage hits the same numbers more than a few times I make note of the highs and lows and go off of that. I agree though, it would be good to know how accurate it is.
Haut, I'll take your advice and pull the riser and give it a look over, I guess I've been curious what's in there any way.
So, from what I'm getting here, the temp gage should read in the 140 area no matter what the lake water temp is??
I'ts colder than the berjeebers here so I probably won't get to this for a month or two, but the boat comes out, and we hit the Mississippi for walleye fishing as soon as we get some temps in the mid 40s.
Any other thoughts or input on the matter is well appreciated.

Thanks again everybody!!

 

[Haut Medoc]

Re: Cold Water Operating Temps

If it runs fine on the mufs, I suspect the impeller even more.....
The added pressure from the hose.keeps good flow at low RPM....
Check the riser, then the impeller.....JK

 

[rogerwa]

Re: Cold Water Operating Temps

I would second the Impeller. Your T-stat on that should be a 145 deg thermostat so if you are seeing 170 in that cold water, you will certainly see higher temps with warmer water.

i had the same behavior where the temp would spike when under 1000RPM and then bumping it up would cool it down. After the impeller change it was rock solid in the 140-150 range. It had been going for a littel while as I would see minor flucutations after high speed runs. Again after the change it was rock solid.

 

[TyeeMan]

Re: Cold Water Operating Temps

Not to beat a dead horse or any thing, , , but again, during the summer months when lake water temps are in the 70s + I could do a wide open run for miles, and follow that up by idling/trolling for hours on end and never see the temp gage go above 150*.
On the contrary, very early in the season or very late in the season when lake water is in the 40s, this is the only time of year I have "trouble". Temp is fine running wide open, then at idle is slowly creeps up to 170* and stays there until engine speed is increased. Only in cold water.
At any rate, I'll go ahead and check all afore mentioned items.
Thanks

 

[Bondo]

Re: Cold Water Operating Temps

Not to beat a dead horse or any thing, , , but again, during the summer months when lake water temps are in the 70s + I could do a wide open run for miles, and follow that up by idling/trolling for hours on end and never see the temp gage go above 150*.
On the contrary, very early in the season or very late in the season when lake water is in the 40s, this is the only time of year I have "trouble". Temp is fine running wide open, then at idle is slowly creeps up to 170* and stays there until engine speed is increased. Only in cold water.

Basically,....... It's Irrevelant.........

If Anything,..... It Should be running Colder,...... Not Hotter.........

 

[Boatist]

Re: Cold Water Operating Temps

I also think the impeller most likely problem.
When the riser plug up usually get hot at high speeds because it can not get enough water thru to keep it cool

Impeller operates two ways at LOW rpms it is a displacement pump and actually moves water from input to output by the vanes being wide at the input then squeesing the vane together and forceing water out at the output. Vanes actually ride against the walls around the inpeller.

At Higher rpms the impeller becomes a cintrifical pump. The vanes colapase and do not actually touch the walls at all.

As impellers get older the vanes that start out straight begin to have a curve in them as they are bent some all the time and at the output side are bent are bent alot. Older impellers will no longer go straight so with the curve they no longer hit the wall in the input area and rather than moving water the water run around the impeller. It will still work at higher rpms when it is a cintrifitcal pump.

In cold water maybe the rubber impeller is even less likely to straighten out and pump water.

Another thing that happends is the walls wear and corode some alowing more water to run around the impeller so at low speeds again water runs around the impeller.

On muff garden hose water pressure will aid the impeller and force water into the engine covering up the bad impeller.

Bottom line in fresh water your engine will get more efficent and run better up to about 190 degrees, and since you do not have to worry about SaltWater deposits from higher temperatures should not hurt a thing.

However if the one of the old vanes break off and clogs a water passage you will not make it back to the dock with out over heating.

So you just have to ask youself one question?

Do you Feel Lucky?? Well Do You?