AlanM Posted March 24, 2007 Share Posted March 24, 2007 What is the optimum water temperature for the fans to cut in, Options are:- Part No. Temp °C Fan 1 Fan 2 50091 88-83 92-87 50101 84-79 88-83 50296 88-79 110-102 50217 88-83 92-87 50113 92-82 95-80 50215 92-87 97-92 50102 93-88 97-92 50035 95-85 102-92 50092 95-90 100-95 50103 97-92 101-96 50214 97-92 102-97 50198 100-95 110-105 These are the only switch combinations I can get to operate the fans independantly. Which one is best? Thanks Quote Link to comment Share on other sites More sharing options...
Kranz Posted March 24, 2007 Share Posted March 24, 2007 Depends if you put the thermoswitch in the top hose or bottom hose Quote Link to comment Share on other sites More sharing options...
Kranz Posted March 24, 2007 Share Posted March 24, 2007 The stock thremostat opens at 82 degrees C (TRD at 71 degrees). Lets work with the std one. Typical operating temperature is 85 degrees C, and is best kept around the for best power. Assuming that the coolant loses not a lot of heat between the stat and the middle of the top hose (where the thermoswitch will be), you should aim for 85 at the thermoswitch. If you get one thats too low, the fans will be constantly on & off. Also above 30mph fans shouldn't really be needed most of the time (unless spirited driving is called for) as air flow through the rad is sufficient for normal cooling (if rad is ducted properly). So I'd suggest 50215 92-87 97-92 as a starting point. If the fans run too much or over cool then move up one or two. And if you have aircon you may want to run a wire to the first fan relay to activate it when aircon is on. Edit - I have a 91-84 102-95.... not tried it yet! Quote Link to comment Share on other sites More sharing options...
AlanM Posted March 24, 2007 Author Share Posted March 24, 2007 Thanks once again, appreciated Quote Link to comment Share on other sites More sharing options...
AlanM Posted March 24, 2007 Author Share Posted March 24, 2007 Does it have to be the top hose, mine is shiney stainless Quote Link to comment Share on other sites More sharing options...
SimonB Posted March 24, 2007 Share Posted March 24, 2007 It ought to be the bottom hose really, as that's after the rad, so the fan will activate if the rad is not cooling enough. Quote Link to comment Share on other sites More sharing options...
JustGav Posted March 24, 2007 Share Posted March 24, 2007 It ought to be the bottom hose really, as that's after the rad, so the fan will activate if the rad is not cooling enough. Indeed, being on the top hose, it will always see the engine tempreature.. and could end up running the engine cold causing enrichment to take place at very cold temps.. As Simon said, you want it after the rad, once the cooling effect of the radiator has done its job. The theory behind the fans is to provide air movement for the cooling function of the rad, this air should normally be supplied by the flow of air due to the car moving. Therefore if the air is cold enough and you are only stationary for a short period of time the rad will still be within its operating efficiency, and you don't want the fan to cut in. If you have something like a Greddy hardpipe on the top, that little threaded section is for a temp gauge, not a thermostat, and using the exact opposite of above, for a tempreature gauge you want to take it at its hottest poing, ie just before going into the rad. Gav Quote Link to comment Share on other sites More sharing options...
Kranz Posted March 24, 2007 Share Posted March 24, 2007 Indeed, being on the top hose, it will always see the engine tempreature.. I thought we were trying to control engine temperature, not rad output temperature?? Top hose temp is controlled by the thermostat, so that is (ideally) where we should try to control to eliminate system lag. Bottom hose temperature is a function of top hose temp and also rad efficiency, but lags way behind. Manufacturers control to top hose temp, and so should we IMHO in the interests of a stable system. Oh, just a bit more info... if anyone wants an adaptor for a thermoswitch to go into a hose I believe the Saab 900's have them in a nice adaptor in the .... top hose Should be cheap from a breakers! Details here http://www.vsaab.com/html/Articles/Cooling.htm near the bottom of the page. Quote Link to comment Share on other sites More sharing options...
JustGav Posted March 24, 2007 Share Posted March 24, 2007 I thought we were trying to control engine temperature, not rad output temperature?? Top hose temp is controlled by the thermostat, so that is (ideally) where we should try to control to eliminate system lag. Bottom hose temperature is a function of top hose temp and also rad efficiency, but lags way behind. Manufacturers control to top hose temp, and so should we IMHO in the interests of a stable system. Ah yes, I see what you are saying... but since the fan is meant to suppliment the air movement, do we not want to monitor when it is outside of its operating range, ie, it is not cooling the water down to the operating temp of 85 (or what ever is selected). PS : Not disagreeing for the sake of an arguement, but rather being genuinely interested in what would be the best way to control it.. Quote Link to comment Share on other sites More sharing options...
JustGav Posted March 25, 2007 Share Posted March 25, 2007 Part of my thinking for my logic, is on VW golfs, the fan thermo-switch is located mid way down on the rad itself, and this is fairly common on most cars. Quote Link to comment Share on other sites More sharing options...
Kranz Posted March 25, 2007 Share Posted March 25, 2007 Ah yes, I see what you are saying... but since the fan is meant to suppliment the air movement, do we not want to monitor when it is outside of its operating range, ie, it is not cooling the water down to the operating temp of 85 (or what ever is selected). Well, it can get into a chicken & egg situation if you know what I mean Consider an engine running at a steady state warming up from cold. As soon as the coolant in the head is up to temp the stat opens, but as the rad is cold the coolant flowing through the rad goes into the bottom of the engine cold, and cools the engine down. The stat shuts again, then opens when the engine gets up to temp again. This pulsation continues, eventually warming the radiator up to operating temp & the stat's work is done (for now). If the airflow throught the radiator is too great, the coolant into the engine cools too much and the coolant into the bottom of the engine drops the temperature of all the engine, causing the coolant through the stat to drop and possibly partially closing the stat. In this way the engine self regulates for too low temperatures. However if the flow through the rad is too low, the coolant coming out of the bottom of the rad is still hot. This passes throught the engine and heats up further. The stat is already fully open, and so it can do no more. The overheated coolant passes into the top of the rad, and still there is not enough airflow to dissipate the extra heat. This is when the rad needs more flow, so a switch in the top hose will cut in and drop the temp of the coolant going back into the engine. The reason the top hose is the place to control & measure all tempeartures is because: 1) its the most stable and is not influenced directly by radiator efficiency 2) head temperature is the most critical & is the hottest coolant cooled part of the engine. It is the most critical as it is directly proportional to the block temperature, and a combination of block and head temperatures in effect 'control' piston crown temperatures (extremely critical). 3) Controling the bottom hose temperature won't necessarily give you the top hose (and engine) temp you want, therefore temperature compensation for timing and fuelling may be up and down with engine temp 4) it is more responsive to thermostat operation so both can work together... in harmony Or if you want just stick it in the bottom hose Quote Link to comment Share on other sites More sharing options...
JustGav Posted March 25, 2007 Share Posted March 25, 2007 Okay, I understand now, what you mean. Cheers for that. Quote Link to comment Share on other sites More sharing options...
Kranz Posted March 25, 2007 Share Posted March 25, 2007 I've had enough of waffling on now. I'll shut up Quote Link to comment Share on other sites More sharing options...
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