New impellor not cooling at low trolling speed

[scottyt22]

I just had a new impellor installed in my mercruiser alpha one v8 1998 - thought this would fix the problem. When trolling at low speed for salmon the engine will heat up to over 170. Have to put in neutral to rev engine or go higher speed to cool engine to acceptable temperature level. What else is causing the temp guage to go way over 170 -- 190/200+ if it was not the impellor in the first place?

 

[JustJason]

Re: New impellor not cooling at low trolling speed

Welcome to Iboats scottyt22.

What V8 do you have? Big difference between a 5.0 and a 454. Better yet, what is your engine serial number?
Have you verified the temps with an IR temp gun, or are you relying on the gauge in the boat?

Did you install the new impellor? Was it just an impellor or was it was it a water pump kit? Did the old impellor come out in 1 piece or many pieced?

 

[crazy charlie]

Re: New impellor not cooling at low trolling speed

Could be risers or check balls.Charlie

 

[scottyt22]

Re: New impellor not cooling at low trolling speed

To answer JustJason's questions:

Question: What V8 do you have? Big difference between a 5.0 and a 454. Better yet, what is your engine serial number?

Answer: Serial Number OF153118 - the engine installation manual on the covers says 5.0L, 5.oLX, 5.7L, 350 Magnum

Question: Have you verified the temps with an IR temp gun, or are you relying on the gauge in the boat?

Answer: I am relying on the guage in the boat.

Did you install the new impellor? Was it just an impellor or was it was it a water pump kit? Did the old impellor come out in 1 piece or many pieced?

Answers: New impellor "kit"; came out in 1 piece.

 

[achris]

Re: New impellor not cooling at low trolling speed

One more question.... Did you use the alignment pins when you put the impeller housing back on?

If you didn't, that could easily account for the problem you have...

Chris...........

 

[scottyt22]

Re: New impellor not cooling at low trolling speed

Q: Did you use the alignment pins when you put the impeller housing back on?

A: I had the impellor installed by a mercury mechanic, so I am assuming he did this correctly and used the alignment pins.

 

[achris]

Re: New impellor not cooling at low trolling speed

Q: Did you use the alignment pins when you put the impeller housing back on?

A: I had the impellor installed by a mercury mechanic, so I am assuming he did this correctly and used the alignment pins.

I've seen plenty who don't use the pins. Usually old school who have been working on the older legs for years and didn't read the manual when the new legs came out (1992)... Most don't even know the pins exist.

One of the checks you could do is a flow test. You need to be pumping (at exactly 1000rpm) at least 3.8 litres in 15 seconds. This is the first test I'd be doing. Download the manual for your engine (#17 in the ADULTS ONLY section of this forum) and look at page 6A-6. Full procedure and expected results.

Chris.........

 

[scottyt22]

Re: New impellor not cooling at low trolling speed

I'm going to go ahead and replace the Risers and all the water hoses. I also learned from Mercuiser support that this engine does NOT have Poppet Balls, which someone said to replace.

 

[joeyr]

Re: New impellor not cooling at low trolling speed

I had the exact same problem with my merc inline 6, MR series outdrive. The problem with mine was the plastic water tube which connects the water pump body assmbly was not properly installed. (inside the lower outdrive)

Unfortunatly, after driving it like that for a month, I found the problem during the autopsy of a cooked engine.

 

[achris]

Re: New impellor not cooling at low trolling speed

I had the exact same problem with my merc inline 6, MR series outdrive. The problem with mine was the plastic water tube which connects the water pump body assmbly was not properly installed. (inside the lower outdrive)

Unfortunatly, after driving it like that for a month, I found the problem during the autopsy of a cooked engine.

Completely different drive, yours is a 'Gen I', Scotty's is a Gen II....

 

[scottyt22]

Re: New impellor not cooling at low trolling speed

I ended up doing the following:

- Replaced Thermostadt (old one didn't work at all when put in hot water)

- Replaced all the water hoses

- Did not replace the Risers, I pulled one of the Risers and it was clean, so I replaced the gasket and re-installed it

With the new thermostadt the boat still heats up more than I'd like, but I'm able to troll at slowest speed longer now, and it cools more quickly when I rev it or speed up.

Next going to replace the Temp Sending unit and check the wire for corrosion.