Overheat after impeller change

[77_starcraft]

1998 Mercusier 7.4 MPI / Bravo I, standard cooling

1) noticed no water out of exhaust, shut down engine before temp got to 190 on dash gauge. No alarm.
2) removed sea pump, impeller missing all blades.

1) replaced impeller, flushed all cooling hoses.
2) removed thermostat housing to inspect for debris. none found, (160 *F t-stat) reinstalled with new gasket.
3) Ran motor on muffs, acceptable flow out of transom exhaust/exhaust boot.
4) continued to run until thermostat temp reached. temp kept climbing, ran until 190 F. shut down.
5) cursed. drank a beer. went to bed

So, the block was partially drained when the circulatar pump hose and t-stat were off, not sure if there is vapor trapped under the t-stat, but each year I drain block and have no problems. The circulator pump bearings seem ok. no leaks.

my plan is to:
1) run it on muff again tonight. prehaps try to loosen bypass hose (manifold to pump) and see if it is full of air.
2) removed t-stat housing and put the whole thing in a pan of hot water. I think the t-stat will be destroyed if removal attempted.

Any ideas? thoughts?
Thanks

 

[HT32BSX115]

Re: Overheat after impeller change

1998 Mercusier 7.4 MPI / Bravo I, standard cooling


2) removed sea pump, impeller missing all blades.

1) replaced impeller, flushed all cooling hoses.

Any ideas? thoughts?
Thanks

Howdy,


You didn't mention the oil /power-steering cooler.

Your missing blades from the last (and possibly previous impeller failures are crammed in the oil cooler and/or associated hoses. Flushing usually will not remove the blockage. I had to remove my oil cooler and extract the pieces from the oil cooler with needle-nose pliers.



Cheers,


Rick

 

[77_starcraft]

Re: Overheat after impeller change

Thanks for the info.

I got 2 large blades out with the backward flush of the steering/fuel/oil cooler circuit. I will look into each one to verify no blockage.
When running the t-stat housing is nice and cold as well as the exhaust risers. the largest hose leading to the inlet of the circulating pump is hot and feels like it has no flow thru it.

 

[HT32BSX115]

Re: Overheat after impeller change

Thanks for the info.

I got 2 large blades out with the backward flush of the steering/fuel/oil cooler circuit. I will look into each one to verify no blockage.
When running the t-stat housing is nice and cold as well as the exhaust risers. the largest hose leading to the inlet of the circulating pump is hot and feels like it has no flow thru it.

I tried to back flush my oil cooler when I removed it and none of the pieces would come out. I had to pull them out literally one by one.

 

[ktbarrentine]

Re: Overheat after impeller change

2) removed t-stat housing and put the whole thing in a pan of hot water. I think the t-stat will be destroyed if removal attempted.

Any ideas? thoughts?
Thanks

Sounds like good time to replace the t-stat. They're cheap.... I had a good bit of work to get my old one out and thought I would destroy it like you said, but it ended up coming out ok (after a good dose of PB blaster and a bit of elbow grease) and actually tested out ok. replaced anyway and feel better about it.

 

[77_starcraft]

Re: Overheat after impeller change

I ran the boat again on the muffs and let it get up to operating temp, without problems. I used a cheap infrared thermometer to measure the temps at various places. The t-stat is working as expected with manifold outlet temp right at 160 F.

I removed both hoses to the oil cooler to inspect and found 1 large impeller fin lodged in the inlet. for those who have not looked inside one it is an array of small (1/4") tubes so it will trap anything larger. one piece melted and clogged one tube so I cleared the clog with a piece if wire.

I also checked the steering cooler since it is 'semi-accessable' and didn't see anything in it.

After re-assembly I started the motor and let it run. the temp gauge went up to 190 again but settled back to 175. I measured hose and manifold temps and all were ok and same as before.

The dash gauge is off by 15 deg. I have already corrected a ground offset problem with a heavy gauge instrument ground wire. before that it was off by 30 deg or more depending on how many accesories were turned on.

Thanks HT32BSX115 for the oil cooler info.

I am going to order all the parts to install a new t-stat as preventitive maintience.

 

[Glass Seeker]

Re: Overheat after impeller change

impeller lost all blades and you only accounted for 3? there are about 8 more stuck somewhere in there

 

[77_starcraft]

Re: Overheat after impeller change

impeller lost all blades and you only accounted for 3? there are about 8 more stuck somewhere in there

I think I got all if not most of the pieces out. there were some in the housing itself. I think there are 8 total. I found an extra pump housing with an intact impeller in a box-o-crap I got from the previous owner, so someone had been in there before.

I took the boat out this weekend and it ran fine, no issues with temps or otherwise.