355 Radiator Fan Fuse Values

I've found that the correct 30 Amp radiator fan fuses in my 355 have been replaced with 40 Amp fuses. Have any other people done this? Do dealers or independent F-car mechanics do this/feel this is okay?

Any owners, with functional radiator fans, using the 30 Amp fuses have problems with them blowing?

I understand it's never a good idea to over-fuse and I know that the fan current can increase with age due to increased mechanical drag etc. I'm sort of thinking I'd rather have a fuse 25% over rating than have one blow, maybe miss the engine temp. warning and damage the engine. I realize a possible consequence of over-fusing is an electrical fire which could be even more catastrophic but I think the chance is really tiny this would cause an electrical fire in this situation (increase from 30A to 40A).

Thoughts/experiences?

 

Mine blew and I replaced it with the same rating fuse. I sorta figured it would blow again, but it hasn't. I cannot comment on the risk of 40 vs 30, but you could put it back and see what happened. Someone may have done it as a "preventive" measure based on some odd intel. Who knows.

 

I have replaced the fuse with 40A and I see no problems. It has been about 6 month now. My mechanic says it's ok.

 

Why did you decide to replace them with 40A?

You can put in 100 amp fuses and you will not see problems.... until that day that something shorts out. Granted it's a big stretch from 40A to 100A!

 

Quite possible, as you mention, that someone put them in as a preventive measure. A better option might be a 30 amp slow-blow automotive fuse (if they exist) since maximum current draw occurs at start-up. There are also circuit breaker replacements available for automotive fuses along with auto-resetting circuit breakers. Might go that route...

 

I have seen 40amp fuses before, on a friends 355 spider. He says they were in there when he bought the car, used. No problems so far. Another friend (aeroengineman) here on fchat had recurring 30 amp fuses blowing and went with 30 amp circuit breakers, the self reseting type, as there are no slow blow fuses available. It worked for a time, but he finally decided to replace the fan motors, which is the real fix, and found it not only fixed the fuses blowing and breakers self-resetting, but found it eliminated his idle drawing down each time the fans started up. (obviously the problem with the fan motors is they start drawing excessive current when they get old and worn, so they are putting extra work for the alternator too)

One risk with high amp fuses, is the fuse panel itself is not really designed for the higher current, so high amp fuses, even to just handle the starting current of the motors, is probably not the best solution. New fan motors is.

Regards,
Dave

 

There is a reason why 30amp fuses are there and there is a reason why they are blowing. You can replace them with 40amp but then that does not really solve the problem. Its like taking meds for something that ails you and never going to the doc to see what the problem is. Sooner or later something is going to let go. When the wires in the harness get too hot then you will be in for major electrical work. Ive seen people over fuse their homes. We usually find this out after the fire.

 

Thanks for the info.

I guess one problem with the self-resetting circuit breakers is you would probably never know if and when (and how often) they are tripping.

As far as idle dropping down when the fan(s) start I would assume it's only for an instant. The idle air control motor should compensate for the extra load from the alternator to get idle speed back to normal (if it's working properly).

Certainly I agree that the fuse panel could be an issue at some point just based on previous F-car fuse panel problems (seem to be marginal, at best).

 

Generally speaking I agree with you that 30 amp fuses are there for a reason. Having said that, Italian electrics and their design leave plenty of room for doubt that they were calculated/done correctly (kind of like their crappy schematics and error-prone workshop manuals). This coming from a fan of just about all Italian cars and owner of a number of different brands over the years (Fiat, Fiat-Abarth, Lancia, Ferrari, Seat (Spanish Fiat, back in the day)...

 

Actually the idle control motor cannot respond that quickly and according to aeroengineman it felt like the engine would die each time, if I remember correctly.

Ultimately new fan motors is the permanent solution. If you are not suffering from idle drop, then the circuit breakers could be a temporary solution...but the problem will not improve, you are only delaying the inevitable replacement.

 

BTW, you can simply put 30 amp fuses back in and monitor and see if they blow or not.

If 5 years of ownership, I have blown exactly one 30 amp fuse for the left (drivers) side fan. I put another 30 amp fuse in and never blown another. If or when it does, I plan to simply replace the fan motors...the are inexpensive: http://www.the-fan-man.com/shop/size-pull-part-2049-p-219.html?osCsid=c5b9027f5137ba744d1d40e666124cd1

 

I agree that the idle speed motor will not move super fast but it should be fairly quick since they're also used to increase idle when the A/C compressor kicks in (which is probably a lot more load than the radiator fan motor(s). Having said that, there may be an ECU anticipation type strategy in some cars that increases the idle and THEN sends juice to the A/C clutch.