Water Temp Question - Is this normal?

[MercMonster]

While out on the lake, I was operating about 5 - 10 minutes at around 2500 RPMs. Came down pretty slowly {10 - 15 seconds} to idle and noticed the temp was close to 180 degrees so I shut it down temporarily and sat until it got back down to 165. The trim is not working as of yet on this boat, but it still seems to be planing out pretty well on its own (take that for what its worth). When I started it back up, I could feel the cool water rushing through the intake hose to the engine and noticed the temperature on the gauge showed an immediate return to around 150 degrees. Both the impeller and the temp gauge and sender are new. What I noticed was that if I slowly, 500 RPMs at a time came down to idle over a small period of time, the temp would hang right around 150, but if I came down from 2500 to idle over about 10 - 15 seconds, the needle would start heading up to 175 - 180 degrees again. I'm not sure the temp rating of the thermostat off-hand, but it is Merc as that is the only type that will fit the housing (its a little-small thermostat). What I'm wondering is if the no-trim situation is causing too much of a load on the engine or can I suspect a water pump or something else? I didn't change the water pump when the engine was out as it looked OK and I knew I could change it without pulling the engine again should it need it. I'm aware of the engine RPMs controlling the speed of the impeller, but 180 seems a little high and I don't feel this is really something normal even though this is my first boat. Idling around keeps the engine around the 150 mark. Any suggestions?

 

[rodbolt]

Re: Water Temp Question - Is this normal?

heat soak is rather normal. however in your case I think its indicating either a failing seawater pump or a restriction someplace.
the pumps in the older R/MR units and most mercs are rather weak anyway and do require attention.
luckily the pump kits are cheap.

 

[ziggy]

Re: Water Temp Question - Is this normal?

my 165 gets the heat soak thing that rodbolt is talking about. but it don't act like yers. my gage stays just under the 4 lines on the temp gage, in the green. sorry, i aint got no numbers, nor a temp gun, only red and green, with 4 hash marks. anyways, my gage stays at just under the hash marks at all but the highest rpm, then it'll only raise a little bit. if i stop. thats when it'll go up. may get up to the 2nd or 3rd line, still in the green. as soon as i start it up. it goes right back to below the 1st line and stays there....so i think there may be something up too.
guess i wouldn't suspect a circulation pump as there's nothing to go wrong with it short of the bush that'll wear, then it leaks.
rodbolts idea of a restriction seems like a good one. where's yer flappers? i've also read that if the waterpocket cover leaks, it could leak exhust gases back into the cooling system and create over heat conditions. did ya do the waterpump houseing along with yer impeller? did ya use a torque wrench to put the waterpump houseing on? those bolts don't take very much torque, specially the back one.....

ya say ya don't know what degree t-stat ya got too. it may be a merc one, but i would guess there'd be two available, a 140 for rwc and 160 for fwc....maybe ya do got the wrong one. temp range for either would be stamped # + 20*....yer almost in the range of the higher tstat. easy test for the tstat is remove it and cook it with a thermometer in the pan and see what it does.

 

[MercMonster]

Re: Water Temp Question - Is this normal?

The impeller, pump base and cover are new and were installed by the shop that serviced the drive. There was just a little wear on the edges of the old impeller, no pieces missing. I just didn't know how long that thing had been in there and was having it all replaced to avoid this sort of thing happening. The flapper is also new, was installed by myself, by the book. There was no evidence of the old flapper hanging around anywhere in the drive, even though it was totally gone save for the metal bracket. I don't boat, nor plan to, in salt water. Even if this does occur, am I looking at hurting anything with the engine temp getting up to 180? I've read here, some say that they operate more efficiently at higher temps, but I don't want to see it get too high. BTW, what is too high of a temp for these old horses?? In the mean time, I'll keep searching for what could be causing the problem and see if I can find a temp. rating on that thermostat.

 

[MikDee]

Re: Water Temp Question - Is this normal?

The standard Mercruiser I/O thermostat is 140 degrees, been using them for years. The hot rodders uaually seek them for their vehicles as required when you put a racing computer chip in, been there, done that.

 

[Don S]

Re: Water Temp Question - Is this normal?

Even if this does occur, am I looking at hurting anything with the engine temp getting up to 180? I've read here, some say that they operate more efficiently at higher temps, but I don't want to see it get too high. BTW, what is too high of a temp for these old horses?? In

While 180? isn't going to hurt the engine at all (the close cooled ones run 175 to 180) the fact that yours is now started going that high is your first WARNING of an impending problem that will probably get worse.
If it has aways run at 160? and now has decided to go up to 180 when slowing down, then something has changed.
As robolt says, a restriction could do it. Exhaust riser, manifold, block full of crap, hose kinked or inside delaminated on hose between drive and transom shield, faulty thermostat.

 

[MikDee]

Re: Water Temp Question - Is this normal?

I Agree, Good Info here ^^^

 

[MercMonster]

Re: Water Temp Question - Is this normal?

This was the first time I ever had the boat in the water. I don't know what is "normal" for this engine or boat itself. It looks like I could run all day at 2500 - 3000 RPMs and the engine temp would stay at 150 or so. It's just when coming back down to idle that it comes back to 180 for a bit. It could be a 160 thermostat and be a normal occurence. I really don't know what is normal here. I'm just asking because I don't know what is normal. Manifold is brand new, Riser is brand new, Thermostat is brand new, Block full of crap is a remote possibility - so how would you test that? All of the hoses, bellows, everything back there brand spanking new. Should I just consider this normal since I don't yet know what normal is and keep an eye out for anything suspicious?

 

[MercMonster]

Re: Water Temp Question - Is this normal?

Well, I just found the box for the new thermostat and it is a sierra 18-3650 and reads Thermostat Kit - 140 Degree. I've yet to find anything that could be causing this. I'm currently running a little rich and plan to correct this here in the next day or so while on the water, but I thought running lean could cause overheat, not running rich. I'm not seeing any sign of a kinked inlet hose. How can I check for block full of crap as Don so eloquently put it?

 

[HT32BSX115]

Re: Water Temp Question - Is this normal?

Well, you could do it the way I did it.

I removed all the round soft plugs on both sides of my 454 and I flushed it out completely... several times. I also allowed the block to completely dry up and used a small piece of clear hose connected to a shop vac and I sucked out a lot more small chips of rust and sand that was in the bottom of the blocks cooling jacket. I could even see inside there and could see the sand and rust that was lying in the water jacket areas. I got a lot out..... just about all of it in fact. I had the engine on a stand out of the boat so it was pretty easy.

I flushed water thru the holes where the circulating pump outputs and back thru the soft plug holes too, several times. This engine is about 10 years old with 122 hrs on it. If was run (raw water) in fresh water only. It also had remnants of a previous raw water impeller failure crammed up into the oil cooler heat exchanger too.

I can't remember if the 250cu-in I6 has plugs on both sides of the block or not. ...

Your results may vary.



Regards,

Rick

How can I check for block full of crap as Don so eloquently put it?