AO Platinum Member
Join Date: Feb 2002
Location: The land that Time forgot
Re: Alfa 155 V6 - Severe Overheating
The first thing is to check that the radiator fan is working.
It should come on at 92C and then stay on until the engine cools down to 90C.
If the fan doesn't work then that's the problem. Any car will heat up in traffic etc, only you never notice it because the fan cuts in and cools it down continually.
If the fan doesn't come on, it could be shagged or it could not be being "told" to kick in..
The temperature gauge you see in the car reads the temperature off the engine block (those wires connected to the thimble shaped protruberance next to the thermostat) whereas the fan only comes on if the water in the radiator hits 92C.
The temperature sender/switch in the rad' is the big brass nut thing on the back/right of the rad' (as you look at it) with 2 wires going to it. When the temp. hits 92C it closes a connection and the fan comes on. It doesn't do anything you can see inside the car.
So, is this sender working? If you unplug the connector you can bridge the connection with a piece of insulated wire. That replicates the effect of the sender when the temp. reaches 92C. With the ignition on, the fan should come on regardless of the temp. of the water in the rad.
If it doesn't come on, the sender could be faulty or the feed to it may be broken. Check the feed (dunno if a simple voltmeter will do it) but the sender is a replace only job.
If the feed is okay and the fan still doesn't work, the fan could be knacked (or leccy to it may be duff). This is much less likely than the sender being defective (age and being immersed in water all its life).
If all that checks out, make sure there is no air in the rad, as if it fills the rad enough, then coolant won't be able to get in to the height of the sender. The sender will think the "coolant" (actually air) is less than 92C and never trip the fan. You have a bleed screw on the reverse/left of the rad' near the top. Just unscrew it slowly till coolant seeps out and that's the rad' bled.
No bullets for Chaingun..