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Question about 740 cooling fan circuit

Re: 92 740 turbo wagon:

Got temp fix on the overheat problem. The fan Autozone sold me as a replacement for the cooling fan was really not strong enough, not enough CFMs, to adequately cool the engine. I did a temp fix on the cracked recovery tank with automotive goop, and pulled the second fan from my (down for a while) Camry. Installed this fan in the

740....its maintaining mid-scale now with AC on and in hot part of the day.

I am going to buy a stronger cooling fan for the 740...actually two of them, on separate fuses. I don't like the stock two-speed fan...its better for reliability to have two separate ones. The camry fan and autozone fan draw 8 amps. THe second fan I could wire up so its switched through a temp switch....there is already some unused temp switch screwed into the RH side of the fadiator, but its contacts are open when the engine is up to operating temp. It might be bad, or might be a N.C. type switch. Anyway I need to know if the coolant is regulated at 180 deg. on this car or what, (it runs at mid-scale on temp gauge) and then I can get some sort of temp switch that closes maybe 5 degrees higher. I won't be red-lining the alternator in this car just adding another 8 amps will I? There are no aftermarket accessories installed that would be pulling more amps that the stock 740 . Thanks Geronimo

Reply to
geronimo
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What rating is the alternator? If need be, you can always pop in a 100A unit from a 740 Turbo but you should have plenty of headroom normally.

Reply to
James Sweet

No, you have lots of spare current available in the alternator. That switch in the side of the rad should close when the coolant gets above a certain temperature, 95 C IIRC, which is above normal operating temperature.

Reply to
Mike F

We got this Volvo from some motorheards who dropped a spare/good engine into it. No telling if the alternator is even a stock one. Unless there is some P/N or info stamped on it, I can't really determine if its 70 amp, 100 amp or what.

If I could be sure that the computer controlled relay can handle 16 amps, I would just wire both 8 amp fans in parallel and let them run together. There is an initial surge of about 12 amps for 24 amps total, so its got to be able to handle that as well. That temp switch is an unknown, it was definitely still open at mid-scale (normal) operating temp. Its got male spade terminals on it, its unused because these motorheads put in a radiator from some other vehicle, and wasn't needed on this car. I guess I could buy an adjustable temp switch, stick the bulb sensor into the radiator fins, and set it so it activates the second fan when the temp starts going a little higher than mid-scale. I guess this might save a little on gas, by decreasing the electrical load on the engine, right?

Geronimo

Reply to
geronimo

Usually there's a big sticker right on it, it'll say something like Bosch 100A in bold letters.

Reply to
James Sweet

Relays usually have a voltage and current rating marked on them. If you have the original relay, it'll have no problem with the 24 amp startup current.

If there's no sticker on the alternator, then run the A/C and the 2 fans and whatever else you'll have on, run the engine at 2000-2500 rpm and see what the battery voltage stabilizes at.

Reply to
Mike F

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