View Full Version: How to reduce engine temperature

Citroen > Trouble Shooting > How to reduce engine temperature

Title: How to reduce engine temperature
Description: A DIY solution to reduce operating temp

silver16v - September 20, 2004 05:20 AM (GMT)

You'll need to get the followings;
1. Thermostat rated 76.5oC or 78oC
2. Citroen BX fan switch available at Asli Auto (Or FIAT fan switch with suitable temp rating)
3. Some wires with a pair of cable lugs


Basically, the thermostat retain cooled water until specified temp for eg. original thermostat is 89oC so the coolant will only flow to engine only when temp reaches 89oC. By changing to lower rating thermostat, it lets the coolant flow before goes higher than 76.5oC.

However it is pointless to have the lower rating thermostat when the car is idling or running at low speed say stuck at traffic jams. This is b'coz the fan will not spin at the right time i.e. electronically controlled by the 'Bitron' box. Unlike when you are on highway doing 110km/h the radiator will be cooled naturally and the low rating thermostat will result to lower temp reading.


In order to get the radiator fans spinning at the right time, here is where we need to use the fan switch. Fan switch has been used for many2 years to control radiator fans but with new technology the radiator fan control has been replaced by electronic control box like 'Bitron', it is more advance as it also control air-cond compressor to stop during high rev & etc.

Depending on the each PSA car models, most radiator have a spare hole for the fan switch, normally sharing the same diameter/tread/size with FIAT cars. The fan switch is a mechanical switch which on/off depending on the rated temp. The BX fan switch is double rated type if i'm not mistaken 92/88 & 88/82. It is good to have something lower as Japanese cars normally using fan switch rated <80oC.

How can the radiator fans work with the fan switch?

The 'Bitron' system will force fan to run second speed if the aircond is not cold enough (A/C refrigerant high pressure threshold is reached) and the signal is connected from the A/C pressure switch @ air-cond drier unit. If you inspect carefully the drier unit is connected with 4 wires, 2 of which is connected to Bitron box for the fan 2nd speed. If these 2 wires is short to each other, the fan will automatically run in 2nd speed. Therefore if we tap from these two wires and connect wiring to the new fan switch, if radiator temp reached the specified temp it will be in contact and and same time shorting the two wires and the fan will run at 2nd speed until the fan switch discontact after temp lowers down to the rated temp. So now the fan will spin at the right time even if you switch off you air-cond & stuck at traffic jams.


silver16v - September 20, 2004 07:14 AM (GMT)
Do not buy Tiara fan switch although it fits in the radiator (and cheaper $ too), the rating is high and not suitable. Make sure check the rating before buying both fan switch & thermostat.

silver16v - September 28, 2004 04:27 AM (GMT)
To understand the radiator fan operation & bitron, chk out the website below (by PEUGEOTLOGIC :thumbs: );

samlsc - September 28, 2004 05:44 AM (GMT)
Silver 16v, But since our engine optimum operating temperature is around 92C, would it be better if we use a higher rating thermostat?

I was thinking of Senthil's mod whereby the temperature sensor is variable. Normally when I drive around town, the temperature's good whereby it's around 80-90 even during jams. But once you start attacking the hills, it lurks up to 100C. Still acceptable, but I thought it would only give me 10 seconds to react if anything goes wrong before my engine goes up in smoke! Maybe i'll rate it lower when I plan to climb hills and put it back to normal mode during normal days?

silver16v - September 28, 2004 06:12 AM (GMT)
try reading the temp gauge when cruising in heavy rainy day (imagine how would it be when driving in cold weather in Europe where the car was designed). You will notice that the oil temp gauge is very low and the engine temp lower than normal. I'm not too sure about the optimum operating temp vs. engine performance, but i guess a slightly higher engine temp makes the engine smoother.

This is based on my own experience just before my car being towed away due to overheating. Once because of the heater hose burst (my previous car zx 2.0 8v) and the other time when i forgot to put on the radiator cap after inspecting coolant (my prevous car wira 1.6). Both incidents i didn't realised the temp coz enjoying the extra ummp due to over heating.

I wish someone can help me install some buzzer or alarm when temp reaches certain temp say 105oC.

My common sense says lower engine temp will prolong engine component lifespan especially rubber & plastic components. You must see what causes engine leakages rubber bushes/seals. It became hard and brittle due to high temp.

oldtimer1035 - September 28, 2004 06:53 AM (GMT)
very easy to install alarm/buzzer if u really want to...a lot of marine engines hv buzzer for water temp & oil pressure...source frm potong shop will be cheaper..must find a place though to install the sensor.
too low a temp an engine will be lethargic,sludge formattion increased and worst of all increase in wear of moving parts...too hot a temp will also hv adverse effects..oil breakdown(so no more protection),cylinder head deformed or warped,burnt gasket....> no more compression so engine konk so tow truck...kekeke
fyi,,,important one here..
if ur engine konks due to overheating pls hv the mechanic check ur compression ratio after being repaired(must be done at normal operating temp)..i once repaired a high power outboard engine that kaput after overheating.once put into water everything seem ok except it died after 20 mins or so of operation..after waiting half an hour or so it start again then after sometimes it died again... stripped back the engine but found nothing wrong..
so the next day called the manufacturer & explain the prob to them.. the remedy was to install a new set of piston seems tht overheating can cause the rings to lose its elasticity,hence the loss of compression...
so overheating can cause structure of metals tochange..for the worse of course

Timothy - December 1, 2004 11:15 AM (GMT)
Great amount of info especially from Silver 16V.
My 16v came with a 91 degree thermostat that I managed to change to a 86 degree one.Can anyone tell me where I can find a lower rated one? Also the Switch modification mentioned is great but I did do it and had a lot of inconsistencies,can someone tell me where I can get it done better as even with the lowered thermostat the engine runs a little hotter than I like when stationary and even worse if the aircon is off as the second fan speed comes in real late. On fans can someone tell me where to find a good replacement motor as one of mine has busted the bearing(can't change because of design) and makes a right racket at high speed.Price at Directional where i mantain the car is about 800 ringgit.Thanks.

Hosted for free by zIFBoards