BB512 radiator fans

on my BB ( 1977 ) I once also had 3 fans in the front of the radiators. I removed thembecause when it was warm outside I had problems with the temperature when I was standing in traffic or shortly after uphill drivinglonger time. so I put in 1 big and one medium fan at the back of the radiators and no problem any more.
originally when the thermoswitch comes to on all 3 fans have been running. but also when I switched on the AC and the water temperature was not as high that the thermoswitch goes to on then the center fan was running only.
so it was when I baught the car, but I can not say f this as I describe has been original.

you cheked already about air in the system? this also let the engine get warmer than normal

 

The schematic in your 512BB OM indicates that all three fans should run whenever the coolant is hot (i.e., whenever the coolant thermoswitch is closed), as romano indicated, and that only the RH fan should run if the coolant is cold (coolant thermoswitch open) but the AC is "on". There is also a relay for each fan so by swapping those around you can determine if one is bad. And finally, the LH fan and the Center fan get their power from the same fuse (#18) -- obviously the fuse itself is OK if the LH fan is running when it should, but the bottom area of the fuseblock where the wire terminals are riveted to the bottom fuse clip could be fried/burned (they cheated a little here by having just the RH fan use fuse #17; whereas, fuse #18 has twice the current since it runs both the LH fan and Center fan at the same time). Good Hunting!

 

I had a problem with the center fan coming on after the temp was already high, so re-wired it to come on with the other two fans, but on a different fuse.

End of possible overheating!

John

 

that would be not bad, but only for the AC you need 1 fan, not more

 

Good day John,

Before rewring... I would check the following:

a. Ensure that the fan rotation is correct... Although the fan(s) may be working they may not be pushing the air in the right direction.

b. Check the voltages at the fan's themselves. If you have OEM fuses blocks they could be old and have the known oxidation/resistance issues with the rivets, etc... thus causing a voltage drop across the blocks and thus delivering less voltage to the fans... Secondly, depending on the load (i.e. current draw) and the the voltage across the block fuse, this can cause a lot of heat at the block leading to some serious block issues (see pic). If you are interested in more info/analysis about the OEM block's design, check out my Boxer Fuse block thread.

c. Check the fan currents. It is possible that the fans are original and so they may have old perhaps worn bearings, dry grease, worn brushes, dirty/worn commutator, etc ... all of which can reduce the rotational speed, but also increases current draw, etc which may cause fuse block issues.

Lastly, if you do decide to hard wire the 3rd fan and do not use a bypass relay, then ensure that the circuit you are reconnecting the fan to has sufficient current capability, as otherwise you could be loading the circuit and cause the fuse to blow... or possibly contribute fuse block problems.

As a frame of reference, my 1977 512BB is wired as per factory and has none of the higher temp issues you have stated. In fact, in the hottest of weather (say 100+F... happens rarely here), the car's temp stay's pegged at midpoint.

Cheers,

Sam
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If you do this rewiring locally at the motors themselves, this will put all of the current thru a single fuse (and will increase the current in one of the relays) = might be some trouble long-term...

PS The photo that Sam posted shows the fuseblock melting at the top +12V input side = that would kill all the fans. If your trouble is at the fuseblock, it would be at the riveted connection in the lower right corner of Sam's photo (but anyone running the stock fuseblocks of this era, on any model, should add some form of soldering to the interconnected metal parts of the fuseblock to not rely just on the mechanical connections to provide good electrical connections - JMO).

 

The fuse block melting wasn't as obvious as shown in the picture on my car. The rivet had gotten hot enough that it was loose. This made the fan operate poorly or not at all.

You have to take the fuse block off to see if it is an issue. Easy to do.

 

Good day Steve,

Since mine were too far gone ...(the picture I posted was from my car when I received it) ... I decided to do something a bit more extreme... The result was I decided to design my own and so I abandoned the OEM fuse style and went with modern ATC fuses, but maintained the same look and original fuse cover, etc.

Cheers,

Sam
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that was a good idea sam
also looks nearly original

 

Always admired your modification Sam (as it uses the original covers) -- IMO it's very, very difficult to do a modification that is a functional upgrade and adds value, but you've done one there. IIRC, didn't you also do the little "satellite" fuseblock for the BBi CIS fuel pump fuses? -- every BBi on the planet should have, and will eventually need , one of those...

 

That's pretty sweet!

Well done.

 

Good day Romano, BT, and Steve,

I am glad that you liked them!

As for the BBi little 2-fuse (fuel pump) block... yup... did those too. Paul (Newman) convinced me to make some, as his were done and few other BBis needed them too. Here is how the design turned out... overall nice and tidy... The fuse cover was previously damaged/distorted and so I hope you will forgive how it looks.

I may design up some replacements for my old 365 Gt4 2+2, as the old bullet style of fuses tend to get cranky over time...

Cheers,

Sam
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Good day John,

One more thing... Take a good look at the radiator and check the fins and/or any fine debris embedded within them. It could also be possible that the rad is not as efficient as it needs to be... either because it is internally corroded or perhaps the air is being restricted from moving through it.

Thanks for the compliment about my blocks! When I first discovered the "high quality", ahem, repair done on my original blocks (the three knackered fuses were bypassed with individual inline fuses) I knew I had to do something... However, what pushed me over the edge was when my car started to cut out and back fire while driving... my instinct told me that all was fine and that something simple was causing the issue. As a consequence I immediately pulled over and checked my fuel pump fuse and low and behold the fuse "clips" were not clamping the fuel pump fuse very well... which was the problem... I was so annoyed at this that after my drive, I went back to my office and started work on a suitable replacement.

Cheers,

Sam