Viscous/Clutch Fan replacement

[Roscobbc]

My '68 big block C3 has always been 'on the edge' relating to overheating in certain summer conditions. Nothing new - anyone with a C2 or C3 Vette will know the scenario of continually keeping an eye on the temperature gauge whilst you gradually 'cook' in summer temperatures. OK so I replaced the water pump some years ago with a high performance Weiand unit. Added-in a new DeWitt OEM pattern aluminium radiator. I've made sure that all rubber seals around the radiator mounting are in place. The is additional stuff making sure the fan shroud is sealed to the front end. I've dropped the front license plate down 6 inches to 'unmask' air flow. Bottom line is that ALL cooling air that comes through the front end ONLY passed through the radiator. And it works - I may still be 'spit roasted' in heavy traffic but the 'sweet spot' cruising in 33 temperaturea is 65 mph at 185 degrees. Yeah, in heavy traffic, major hold-ups etc it'll hit 190/195 but thats about it. TBH winter is more of an issue in keeping it over 150. Last few days in the 30-32 temperature its been running at 200-210. Still running OK but IMHO 'on the edge' on boiling over. Which is exactly what happened - guage went off the scale and off it went.
The one thing I had never replaced was the viscous fan coupling. Obviously the original item and whilst the fan bearing seemed fine you'll see in the images a small amount of greasy crud around it which could be indicitive of the silicon fluid leaking. A proper test is when the engine is fully warmed up (and fan engaged) to stop the engine and attempt to rotate the fan blades. There should be significant resistance to rotating...........mine, same as when cold.
Anyway I sourced a new one and we're now back to 175 - 185 summer running urban temperatures once more.........seemingly.

 

[Chuffer]

I think it`s time to check my fan out too . Never over heated yet and usually cruise at 190 ish and often less in colder weather . It was running 200 and occasionally 210 on the way home from the blisteringly hot Nationals but was at least running ok with no clouds of steam to spoil the view .

 

[Roscobbc]

I think it`s time to check my fan out too . Never over heated yet and usually cruise at 190 ish and often less in colder weather . It was running 200 and occasionally 210 on the way home from the blisteringly hot Nationals but was at least running ok with no clouds of steam to spoil the view .

The last CCCUK nats I took the Vette to had temperatures on the day of 33 degrees. Logic said that a lower cruising speed (like 50 - 55 mph) would see lower running temperatures - plus the advantage of keeping convoy with HGV's on 56 mph speed limiters. No so, in fact it ran cooler at 65 mph and about 2400 or so rpm. Thinking that airflow through the front end obviously must have something to do with it all I tried 70 mph, 75 mph etc but running at these speeds simply raised the running temperature. I'm guessing that each C3 variant will in fact have its own 'sweet spot' speed for minimal temperatures, with the later cars no doubt running coolest of all.

 

[Chuffer]

The last CCCUK nats I took the Vette to had temperatures on the day of 33 degrees. Logic said that a lower cruising speed (like 50 - 55 mph) would see lower running temperatures - plus the advantage of keeping convoy with HGV's on 56 mph speed limiters. No so, in fact it ran cooler at 65 mph and about 2400 or so rpm. Thinking that airflow through the front end obviously must have something to do with it all I tried 70 mph, 75 mph etc but running at these speeds simply raised the running temperature. I'm guessing that each C3 variant will in fact have its own 'sweet spot' speed for minimal temperatures, with the later cars no doubt running coolest of all.

Yeah , I found that temp crept up a bit more once I cruised at about 70mph but ease off a bit and would slowly come down a bit .

 

[HJG]

My big block runs bang on 210 90% of the time. Sometimes a tad under if it's cool outside and sometimes a tad over when at 70mph. Viscous fan is good.

 

[Roscobbc]

I suspect a later BB (like SBC's) will be optimised to run at the temperatures you mention - on mine at these temperatures, whilst not in the true sense overheating the fuel system, carb etc is 'on the edge' and will certainly exhibit signs of percolation and lumpy running.

 

[Oneball]

There’s a second test for viscous fans as well as the hot test.

With the engine cold and off there should be significant resistance to turning the fan. You should notice this when you start the engine from cold. The fan will turn quick for 20 seconds or so and then slow down as the coupling becomes free. You should then be able to stop it with a rolled up newspaper while it’s still cold.

 

[HJG]

Ah the good old newspaper test...remember it from my BMW E30 days!

 

[Oneball]

Ah the good old newspaper test...remember it from my BMW E30 days!

E34 for me.

 

[Chuffer]

I suspect a later BB (like SBC's) will be optimised to run at the temperatures you mention - on mine at these temperatures, whilst not in the true sense overheating the fuel system, carb etc is 'on the edge' and will certainly exhibit signs of percolation and lumpy running.

According to my 1980 C3 owners handbook , a 200 degrees reading on the temp gauge is " engine overheating " . I would have expected the needle getting on or near the orange zone approaching 260 degrees to be " overheating" . How did these cars cope back in their day in down town California on a hot day ?

 

[HJG]

Interesting Chuffer. This is from the 1969 manual:

 

[Chuffer]

How bizarre ! I have to say , your handbook sounds much more plausible to me . My handbook is a repro so maybe somebody made it up as they went along !

 

[Adtheman]

My '68 big block C3 has always been 'on the edge' relating to overheating in certain summer conditions. Nothing new - anyone with a C2 or C3 Vette will know the scenario of continually keeping an eye on the temperature gauge whilst you gradually 'cook' in summer temperatures. OK so I replaced the water pump some years ago with a high performance Weiand unit. Added-in a new DeWitt OEM pattern aluminium radiator. I've made sure that all rubber seals around the radiator mounting are in place. The is additional stuff making sure the fan shroud is sealed to the front end. I've dropped the front license plate down 6 inches to 'unmask' air flow. Bottom line is that ALL cooling air that comes through the front end ONLY passed through the radiator. And it works - I may still be 'spit roasted' in heavy traffic but the 'sweet spot' cruising in 33 temperaturea is 65 mph at 185 degrees. Yeah, in heavy traffic, major hold-ups etc it'll hit 190/195 but thats about it. TBH winter is more of an issue in keeping it over 150. Last few days in the 30-32 temperature its been running at 200-210. Still running OK but IMHO 'on the edge' on boiling over. Which is exactly what happened - guage went off the scale and off it went.
The one thing I had never replaced was the viscous fan coupling. Obviously the original item and whilst the fan bearing seemed fine you'll see in the images a small amount of greasy crud around it which could be indicitive of the silicon fluid leaking. A proper test is when the engine is fully warmed up (and fan engaged) to stop the engine and attempt to rotate the fan blades. There should be significant resistance to rotating...........mine, same as when cold.
Anyway I sourced a new one and we're now back to 175 - 185 summer running urban temperatures once more.........seemingly.


View attachment 12602View attachment 12603View attachment 12604View attachment 12605

i only run a 350 sb but i changed to a dewitt with a dual electric spal set up. with a 195 thermostat works a treat, also have a toggle switch under the steering column which i switch on if in heavy traffic.

 

[CaptainK]

My 327 seems to run pretty much exactly like HJG's picture above from the manual all the time. When in hot slow traffic then it goes up a tad, closer to 210, but not much.

The only time its read higher than that is when my Vette decided to do a steam train impression - the water pump bearing had died and it just tore itself apart on the motorway and thus gushed hot water everywhere and clouds of steam were pouring out. Car was ok as I stopped immediately, just needing a new water pump. Amusingly, I was taking the Vette to my "local" Yank specialist for a checkover and service. I had maybe 15 more miles to go to get there.... and that was covered on the back of an AA truck.

 

[Chuffer]

I have just checked the viscous coupled fan on my 1980 C3 and it has very little resistance to being turned by hand when engine is off . It rotates well enough with engine running but obviously I have no idea how much it slows down once motoring along . Oddly , I tried the rolled up newspaper trick whilst engine was running from a cold start up and ended up with confetti ! The fan did not stop rotating .

 

[Roscobbc]

I have just checked the viscous coupled fan on my 1980 C3 and it has very little resistance to being turned by hand when engine is off . It rotates well enough with engine running but obviously I have no idea how much it slows down once motoring along . Oddly , I tried the rolled up newspaper trick whilst engine was running from a cold start up and ended up with confetti ! The fan did not stop rotating .

Viscous fan operating parameters are much like they are for PCV valves - everyone uses them as a matter of course but there is relatively limited understanding and even less technical information out there.

 

[Chuffer]

Viscous fan operating parameters are much like they are for PCV valves - everyone uses them as a matter of course but there is relatively limited understanding and even less technical information out there.

So it is yet another `Dark Art ` then Ross ????

 

[Roscobbc]

Not really so much of a 'Dark Art' Chuffer more like one that is likely to be forgotten soon (much like thermostat replacement) - the Hayden 2711 seems to be a generic replacment. The Bi-metal themostat spring (helical) on the 2711 differs from the 'flat metal' one on the old OEM unit - known as the Schwitzer unit. This is about 3 or 4 times the cost of the 2711 and supposedly 'heavy duty'...........anyway 170 degree operating temperature is exactly what I need so will see where it all goes. Further info on couplings can be seen here and makes interesting reading - https://www.rockauto.com/genImages/93/haydenSD-HD-SVRD.pdf - Have to say that some of the HD and Super HD units are difficult to source and seriously pricey.

 

[Chuffer]

Thanks for the info Ross .

 

[Vetman]

My understanding is that ideal engine temperature is about 212 deg F so that water in the oil caused by combustion blow by is boiled off.

Also C3 gauges have the pointers in the vertical position generally so that you can just scan the set to see all is well.