tachometer settings

[mstng]

My 3.0 volvo has been running at WOT max of 3400 RPM's where I was expecting 4400. Would the fact that the back of the tachometer is set to the 6 cylinder setting instead of 4 account for this much difference?

Need to troubleshoot a overheating issue before taking it out, but was just curious about what I can expect when I run it at the correct setting.

Thanks

 

[HT32BSX115]

Re: tachometer settings

My 3.0 volvo has been running at WOT max of 3400 RPM's where I was expecting 4400. Would the fact that the back of the tachometer is set to the 6 cylinder setting instead of 4 account for this much difference?

Need to troubleshoot a overheating issue before taking it out, but was just curious about what I can expect when I run it at the correct setting.

Thanks

You're not getting accurate rpm with the tach set wrong. don't believe what you have on the tach until it's set right. (and even then if you don't verify it with a known tach it may STILL be wrong)


Regards,


Rick

 

[Silvertip]

Re: tachometer settings

Ahhhh -- yes, the tach setting does make a difference. A 6 cylinder engine produces 3 ignition pulses for every revolution of the engine. A 4 cylinder engine produces 2 ignitions pulses for every revolution of the engine. Therefore, on the 6 cylinder setting, the tach has a 33% error on the slow side so adding 33% to your 3400 rpm reading produces 4520 RPM which is about right for that engine.

 

[mstng]

Re: tachometer settings

Ahhhh -- yes, the tach setting does make a difference. A 6 cylinder engine produces 3 ignition pulses for every revolution of the engine. A 4 cylinder engine produces 2 ignitions pulses for every revolution of the engine. Therefore, on the 6 cylinder setting, the tach has a 33% error on the slow side so adding 33% to your 3400 rpm reading produces 4520 RPM which is about right for that engine.

Bingo.....

Thank you very much Silvertip. Without the speedometer I wasn't sure, but it seemed I was moving along pretty good. Had to be max speed for this boat. I hope this proves true when I get it in the water. Taking it to a mech next week. This overheating problem has me stumped. I'll have him verify with a shop tach.

 

[chiefalen]

Re: tachometer settings

Whats the over heat condition?

 

[mstng]

Re: tachometer settings

Whats the over heat condition?

2003 Volvo 3.0 GLP-B chaparral 180 with 49 hours bought a couple weeks ago from a trusted friend. Had been run once the last year and supposedly flushed adequately (salt water use).

Test run while on muffs saw temp while flushing go to 180 and immediately drop to 160's then steady at 175. Thermostat seemed to work fine.

Tested while underway, could not get RPM's above 2200 and speed was obviously slower than expected (because of incorrect tach settings was in reality probably in the 3000 or above range). Temp remained stable though at 178.

Changed impeller that looked brand new, and while changing plugs I found one that broke off while removing the boot. I found that I had been running on 3 cylinders. A huge difference the next time it was run with Rpm's now up to 3400 (in reality, probably at spec of around 4400).

Temp however began climbing whenever I got above 3400. Seemed steady at 180 yet up to 210 when WOT. Never let it get above that, and never let it stay there for more than a few seconds. Reduced throttle and back to 180.

Did complete tuneup-cap, rotor, plugs, pump fuel filter, inline fuel filter, drive oil, engine oil and filter, thermostat.

Checked thermostat in the kitchen and it opened and closed at specs. Thermostat housing had some less than pea sized gunk that cleaned out. Changed it anyway.

While running on flush adapter yesterday it overheated to 210 again and I gave up. The heat issue doesn't seem related to whether or not I am on plane, or related to the thermostat. I also ensure that my flushing cap is tight so as not to draw air. I am guessing that since it ran fine earlier at low rpm's without overheating, yet now even with just a flush and idle it overheats that while I was running at WOT I may have broken some gunk loose and have an obstruction somewhere.

I have tried a bit of half-assed flushing, and may give that another shot today as I haven't flushed the power steering hose. I may also have another look at the impeller housing and tighten the 4 screws more. Would no overheating with the thermostat removed tell me anything even though we know that we have a good thermostat? I can easily take it out. I have read Don's link to the overheating article and am starting to feel this is better left to the professionals. I do anesthesia for a living and try to know my limitations before causing permanent damage. I hope I haven't already done so with the 210 temp.

Anything simple you can suggest short of checking the riser and manifold or running clear hose testing?

An unrelated question: I remember that on outboards it seemed that a spin of the propeller with a finger would cause several revolutions. Should I expect this with and IO? It takes effort to spin this one.

 

[kkr26]

Re: tachometer settings

I got my new boat V8 VP5.0. Tach was maxing at 3k adn the switch on the back was set to 12 pole. I switched it to v8 and no probelm since.

 

[captmello]

Re: tachometer settings

Sounds like you have a flow problem in the system. Salt water eats those mainfolds. You may be at the end of life expectancy. If they're not shot now, maybe in a year or two. You may pay a mechanic $100 to say the same thing. I don't think you can test for corrosion. As long as you've checked all the lines you can for blockage, you may want to just change the mani and riser.

Good Luck!!

 

[chiefalen]

Re: tachometer settings

The impeller did not break apart before you changed it?

If it did then might be pieces in the system.

You have a heat exchanger? If yes that has to be cleaned out, they always get gunked up.

You have a engine mounted water pump? If yes, than maybe the vanes are gone.

Then finally the riser.

If all else fails and the condition still there than the riser got to be pulled.

I don't know if you have a flapper on the exhaust tube.

If yes those break off and clog the exhaust.

5 years in salt water for risers, just is what it is.

My money is on the exchanger clogged first, but even bets it's the riser.

Or both.

 

[mstng]

Re: tachometer settings

Just for reference in case someone searches for tachometer settings. My setting on the tach was for 6 cyl. When running at WOT after changing to 4 cyl I ran at 4600 and matched specs instead of the 3200-3400.