More questions '92 740 cooling system....

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- geronimo
  
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posted
17 years ago

Mon, Jul 17, 2006 5:17 PM

James (or anyone):

Re: '92 740 GLturbo overheating. replaced shorted electric cooling fan...still running hot. I am swapping in my spare 740 radiator, and have a new cooolant recovery tank coming from FCP Groton. I was just wondering if there is any way that you could overfill the system? The cap has an integral relief valve in it though doesn't it? An overheat or overpressure is supposed to vent out of the cap, saving the tank from cracking, isn't it?

When I have the new radiator installed, what is proper way to fill the system? With no fill cap on the radiator itself, how do you get the air out and ensure that the system is really full? What I have been doing is just addding water until mid-way on the reservoir; start car, and then add enough to bring it back to mid-level.

2nd question is... does your 740 have working AC, and do you switch in a second fan when the AC is on? Seems like the 89 Volvo sedan I used to have had an auxiliary fan that normally ran when the AC was on.... If yes is the answer, then I definitely need to get a second 12 in. fan and wire it up to come on with the AC....or just have two fans running all the time. With only one 12 in. fan alone, no mechanical fan, should it be sufficient in S.Texas summer climate...if you have a healthy cooling system, proper coolant mix, etc? (here in summer is the closest thing to hell imaginable) Geronimo

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- Perry Noid
  
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posted
17 years ago

Mon, Jul 17, 2006 7:00 PM

consider a leaking head gasket, allowing hot gases to escape from cylinder(s) into the coolant, causing the high temp and possibly rupturing the overflow tank....

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- Peter K L Milnes
  
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posted
17 years ago

Mon, Jul 17, 2006 11:57 PM

I am running my 945 with a 960 radiator fan having removed the mechanical item. So far I have not needed to switch it on to avoid overheating.

All the best, Peter.

700/900/90 Register Keeper, Volvo Owners Club (UK).

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- Mike F
  
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posted
17 years ago

Tue, Jul 18, 2006 12:16 PM

The rad from your '89 is not the same as on the '92. The one from the '89 is smaller, and had no heat exchanger for the engine oil. The filler cap on the expansion tank includes 2 valves - one to let excess pressure out, and another to break the vacuum that occurs upon cooling. I would suggest a new cap to make sure all that is working properly. The expansion tank is the highest point in the system, pressure changes and flow will ensure that the air ends up there. Just keep topping it up as necessary after any work on the cooling system that results in any loss of coolant. You'll probably see 3 nearly identical switches on the condenser (visible with the grille removed). These switches send pressure signals to turn on the standard 2 speed electric fan on low speed, then at a higher pressure, high speed, then at a higher pressure still, turn the compressor off. (Note that the fuel computer actually does the switching of the relay - so it can turn the fan on as needed based on coolant temperature as well.) Whether one 12 inch fan is enough, that depends on the fan. Since you don't seem to have the original fan, and have room for a second one, find the fan relay (or the wires to it) and use one fan as low speed, and the second as high speed.