HOT 16 Valve
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Thread: HOT 16 Valve

  1. #1
    Join Date
    Jan 2006

    Default HOT 16 Valve

    Yesterday while crawling in the city link carpark the temp gauge of my 16V got to 100 or so without the radiator fans cutting in. Faulty temp sending gauge or is it managed by the Engine Management System. Can system be bypassed? Any other ideas or suggestions.


  2. #2
    Member ozziediver's Avatar
    Join Date
    Aug 2003


    Check your fan thermoswitch in lower right corner of the rad - has a plug with 3 wires on it. With ignition on, heat it up with a small torch and see if both fans kick in on low speed, keep heating and they should both then switch to high. Mine went this week as well, fans only cut in on high at high temp and by that time engine was at 100C - lucky I had a spare new one to swap. There's a way to put a relay in the circuit as well to take the load off the switch - should be in a recent post from Jack Z.
    1991 BX TZD
    1990 BX 16V (x 2)
    2004 307 Touring
    1990 Mitsubishi Express Van: Alpaca Transport:

  3. #3
    1000+ Posts Ken W's Avatar
    Join Date
    Sep 2002
    North Brisbane


    Unlike a BX 8 valve, the BX 16 Valve seems to have a few larger parallel pathways for the coolant to flow from the head outlet back to the water pump other than through the radiator. I think this serves two purposes, to reduce the pressure head on the water pump so you get more power to the wheels, and to even up the temperature in the engine thereby reducing temperature stress. However, the downside is that if the radiator gets a little blocked, much less coolant goes through it and more goes via the alternate paths.

    Another quirk of the BX is that the temperature sensors are situated on the outlet of the radiator measuring the cooled temperature not the engine exit temperature. Also the 16 Valve temp sensors are set higher than an 8 valve. So if the radiator is a bit blocked, the engine temperature can get get quite a bit higher than the radiator exit temperature. This is also exacerbated by overall reduced coolant flow during idleing or slow carpark driving.

    Dave was having these issues with his 16Valve and we found that as well as the main radiator bypass, his heater had also been bypassed so we blocked that off. We also fitted a standard 8 valve temperature sensor and that improved temps in normal driving. However, there were still problems when driving in heavy traffic. His radiator has just been cleaned and it was only 35% blocked.

    I would suggest that BX 16Valves need very clean radiators, and should use no lower than 33% mix of coolant so that the boiling point is above 127 degrees C and make sure the system is well bled to keep the pressure under control. Also, I wouldn't use any bars leaks or other similar products on a 16 Valve, as these have suspended solids which will reduce radiator flow.

    So that's my

    Good Luck,

    Ken W

  4. #4
    Join Date
    Sep 2005

    Default hot bx

    I was recently also suffering from a hot bx. The fan switch as mentioned earlier wasn't working so that needed to be replaced. The car was still far too hot in slow traffic. On the open road the temp was fine, but as soon as you stopped at lights the temp would go up and stay up. On a 35 deg C day I had the car running in the drive way with the bonnet up. The fan would cycle on and off and temp continued to rise until the pressure was enough to overflow the coolant expansion tank.

    Recently I have replaced the radiator. The old one was stuffed. It was leaking in one spot, rotten in others and most of the rest seemed blocked. Now it seems to run much cooler. On the open road it sits on about 80 deg c. At lights the temp rises to about 90 deg c then soons drops down as soon as the traffic moves again.

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