Running too cold, now too hot

schoolsOut · **Posted:** Sat Jun 08, 2013 2:47 pm

My 2005 210 Horizon was running pretty cold this season. Probably around 135-140 degrees according to the gauge. I don't remember it running that cold last season. I pulled the thermostat and tested it in warm water and it appeared to open and close as it should. I put the thermostat back in and replaced the impeller while I was working on it. Then when I ran the boat on the hose, it wanted to get too hot. It got up above 175 degrees and eventually the alarm sounded, so I shut it down. The large water hose running into the thermostat was hot and had a decent amount of water pressure. This seems to indicate that the thermostat would not open. Just a bad thermostat, or something else?

NiagaraChillin · **Posted:** Sat Jun 08, 2013 8:36 pm

schoolsOut wrote:

This seems to indicate that the thermostat would not open. Just a bad thermostat, or something else?

Sounds like it. Pull the T-Stat out, run it on the muffs and see where the temp is at. Should be low again. If it doesn't overheat, then it is the T-Stat. If it does, then maybe some kinda blockage?

schoolsOut · **Posted:** Sat Jun 08, 2013 9:00 pm

NiagaraChillin wrote:

schoolsOut wrote:

This seems to indicate that the thermostat would not open. Just a bad thermostat, or something else?

Pull the T-Stat out, run it on the muffs and see where the temp is at.

I will give that a try tomorrow. I was going to wait until my new t-stat arrives; I have one on order. Should be arriving early next week. Running it without one will give me some piece of mind that it is not anything else. I was hoping to get to the lake tomorrow which is why I threw the old one back in after testing it.

Just to clarify...when I run the boat on the hose, I use the blue-capped water hook-up (Volvo-penta) instead of muffs. That is just as good right?

ric · **Posted:** Sat Jun 08, 2013 9:14 pm

Sounds like t stat. They're supposed to stick open when broke. In my 17 years of working on cars I've never seen that

230 Mike · **Posted:** Sat Jun 08, 2013 11:49 pm

I'll ask the dumb question - are you sure you didn't put the 'stat back in upside down? The "blue port" is supposed to be OK, but be sure you get the cap back on tight, otherwise your impeller will suck air into the system along with raw water, which will cause overheating. That cap needs to be airtight.

schoolsOut · **Posted:** Sun Jun 09, 2013 9:21 am

230 Mike wrote:

I'll ask the dumb question - are you sure you didn't put the 'stat back in upside down? T

Definitely a reasonable question. I put the thermostat in with the spring-side up. The water hose runs from the pump up to the top of the t-stat housing. So the spring, side was on the side of the water inlet. That is the way the other came out, and it makes sense that it would be that way.

230 Mike · **Posted:** Sun Jun 09, 2013 4:28 pm

I haven't had mine out, but I thought the spring side always went down.

http://www.volvopentastore.com/Circulat ... _id.790785

schoolsOut · **Posted:** Sun Jun 09, 2013 5:22 pm

230 Mike wrote:

I haven't had mine out, but I thought the spring side always went down.

http://www.volvopentastore.com/Circulat ... _id.790785

Hmmm...I am nearly certain that my spring was facing upward into the housing when I took it out. My dad was with me when we took it out and he thought so too. In what direction does the water flow? Does it flow through the big hose up to the thermostat? If so, wouldn't the spring have to be up there? The diagram that you linked, sure looks like the spring faces down. I will do some experimenting tomorrow. Thanks, Mike!

LouC · **Posted:** Sun Jun 09, 2013 6:33 pm

http://www.crowleymarine.com/johnson-ev ... /57011.cfm

Closest diagram I could find, I can't look up Volvo diagrams but this is the joint venture model shared with OMC and Volvo. As you can see the spring goes DOWN pointing toward the intake manifold. The stat is held in the thermo housing by a rubber O ring.
The water flow is as follows: cold engine, the water flows in from the impeller and when the 'stat is closed, the water goes into the bypass passage in the thermo housing and then out to the manifolds and risers. The water in the block/heads stay in there and is recirculated till the temp gets hot enough to open the stat. Then the stat opens and the hot water in the engine, gets pulled out by the circ pump and mixes in with the cool water from the impeller. So at this point some of the cool water from the impeller gets sucked into the engine and the warm water coming out of the engine exits the ports that feed the manifolds. So you see the thermostat when it opens lets hot water OUT of the engine, replaced by cool water from the impeller.

The spring end has the temperature sensing pellet to open the stat, it has to be in the HOT water for it to open. If it was in the cold water supply end it would never open.

schoolsOut · **Posted:** Sun Jun 09, 2013 9:36 pm

Just did some extensive reading in my Seloc repair manual. I now have a better understanding of the cooling flow on my motor. This is my first boat and I bought it near the end of last season. I grew up on boats, but never had to be concerned about the inner workings in the past. Thanks for pointing out my incorrect thermostat installation! I will correct that tomorrow.

I'm a bit of an obsessive wacko when it comes to my boat and I have been losing sleep over one other thing that I noticed after running the boat on the hose on Saturday. After it began to overheat and I was looking closely at the front of the motor. A drip appeared to fall from the impeller housing into the bilge a couple of times. The housing was pretty wet with condensation from running on cold water from the garden hose for so long while waiting for the engine to warm up. I had just changed the impeller and o-ring. Impeller housing bolts were tight. Should I be concerned about the drips or do we assume it was just the condensation?

Thanks for all of your help. Wish I could buy you all a beer!

LouC · **Posted:** Sun Jun 09, 2013 9:40 pm

Hard to say but if you can run it on a nice warm dry day then you should not get condensation. Those Volvo impeller housings can leak sometimes and if you have a water leak you can have air being pulled in which will reduce the volume of water to the engine.

When I change the impeller on my OMC Cobra I always check for water leaks from the impeller housing when running it on the water hose.

Graham R · **Posted:** Mon Jun 10, 2013 4:26 am

There is a replaceable seal on the water pump shaft, it's not expensive.. The one on mine failed at the tail end of last year. When they fail, it results in a drip of water out of the "weep hole" in the pump body. At idle it just drips out, but at higher RPM water will be sprayed by the water pump pulley all over the front of the engine.

Not so bad with fresh water, but in my case it was saltwater. I was lucky that I caught mine fairly sharpish, it was only the pump pulley and body that had suffered ( all the paint fell off). In theory, the seal can be changed without removing the pump. It practice it's easier to remove the pump and repair it on the bench. That way you can be sure the new seal has gone in square.

230 Mike · **Posted:** Mon Jun 10, 2013 7:08 am

schoolsOut wrote:

I grew up on boats, but never had to be concerned about the inner workings in the past.

Kind of ups your appreciation of your dad, doesn't it?

pet575 · **Posted:** Mon Jun 10, 2013 12:14 pm

I know you are pretty confident you have this licked but did you inspect that old impeller closely to make sure none of the vanes had come off or chipped?

Just trying to eliminate blockage as an alternate cause in case this one doesn't end up being the thermostat.

schoolsOut · **Posted:** Mon Jun 10, 2013 2:01 pm

pet575 wrote:

I know you are pretty confident you have this licked but did you inspect that old impeller closely to make sure none of the vanes had come off or chipped?

Just trying to eliminate blockage as an alternate cause in case this one doesn't end up being the thermostat.

Here is the impeller:

One vane is missing. Not sure where it went. Unfortunately with the monsoon here in the northeast, I was not able to do any troubleshooting today. Hoping to reinstall the t-stat tomorrow. I will let you know how it works out. Hoping for no blockages.

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Running too cold, now too hot

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