Tachometer on fan/clutch

[jcolegrove]

Well, have noticed after the RT temp guage mod the needle moving a bit, so with 112k suspecting the fan clutch. bought a 30 dollar optical tach and here are the results on a completely warm engine: (190 deg. coolant)

idle- 700 or so rpm fan speed
2000 rpm engine speed- it drops! to 450 or so...
back to idle, back to 700 rpm or so..

checked the tach w/ the other car and seems spot on. also, just visually watching the belt go by, it 'looks' as if it slows down...

now, with coolant temp at 190 deg., shut off engine and one can turn the fan easily.

so..... seems the clutch is gone? or is conceivable that this is normal at this temp? was the engine not hot enough? interesting at the very least, and i'll say that these tachs are great fun! and apparently very useful... will be checking other cars, etc...

thoughts?

 

[John E Davies]

It's not the temperature of the coolant in the engine block that triggers the clutch, but the hot air flowing out of the radiator core. Unless you are driving around you won't get the fan clutch to do very much - you have to load down the engine and get the coolant completely heat soaked.

John Davies
Spokane WA

 

[alkaline747trio]

Go drive, get the engine hot, bring it back and let it idle. If the fan clutch is already engaged, then you will hear the fan slow as it cools. With my 3F-E, it is very obvious when the fan engages and disengages.

OR

On a COLD engine, start and let idle. When it gets up closer to opp. temp., then you will hear the fan engage.
EDIT: after it has idle'd closer to 200*, then rev a few times untill fan speed changes at idle speed (check fan speed, rev a few times, check again).

 

[landtank]

at 190* i'd expect your fan to turn easy. Your close to ideal temps so no need for cooling.

 

[bigbrowndog]

This tach would be great to get some standardised readings at certain revs and temperatures for comparisons to judge how efficient fans are working.cheers