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Re: Head gasket problem..maybe..need help Posted by Saana88 [Email]  (#207)  [Profile/Gallery]
(more from Saana88) on Thu, 17 Nov 2005 15:50:36
In Reply to: Head gasket problem..maybe..need help, Todd  [Profile/Gallery]
, Wed, 16 Nov 2005 18:28:13
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Here comes the hot running advice: If your car still has its original expansion tank (coolant reservoir) cap (it's black), replace it. If the cooling system cannot pressurize, it cannot do its job efficiently. Also, if your 900 runs hot, it's either the thermostat stuck close (replace every five years max), the connectors in the cooling fan relay corroded (it's bolted to the left front fender inner panel, between the wheel arch and the headlights) or the radiator fan thermoswitch (screwed into the upper, driver's side of the radiator with two wires connected) going south. I had two out of three (thermoswitch and corroded relay contacts) on my '88. My mom drove it for two and a half years and I drove it for six months with these two things (and the automatic, more later) making the car slightly overheat. A ten dollar thermoswitch and some good rust-removal on the contacts and the temperature gauge never read over half anymore.
If the car gets hot (temp gauge over two-thirds) and the fans don't turn on, the thermoswitch is bad. If you short-circuit the connectors on the thermoswitch and the fans don't turn on, the wiring or relay or both are bad. If the fans shut off when you turn the car off, even when the motor is still very hot, or if the fans only run for five to fifteen seconds at a stretch, the relay is faulty.
After two years, my mom (previous owner) overheated the car. A month later we noticed the head gasket was leaking. Symptoms of head gasket failure include rough restarting, but the telltale sign on my car was the sudden vomiting of coolant as it boiled over out of the reservoir cap 5-15 minutes after switching the car off around a quarter of the time.
A quarter of the time? Assuming everything else works, you have a 1 in 4 chance of the cylinder where the gasket failed stopping under compression. Normally, there's nowhere for that pressure to go, and it slowly bleeds out of the valves. When the head gasket is failed, there is somewhere for that pressure to go and it bleeds into and overpressurizes your cooling system. This also means coolant (in the engine water jacket) can touch hotter metal in the combustion chamber than it normally sees. This also overheats the coolant, and after that 5-15 minute period elapses, the coolant boils over out of the coolant tank cap, usually around a quart at a time. The puddle will form inside of the left front wheel.
Hopefully you don't have any of those symptoms, your head gasket is still intact (not really an issue unless you really overheat the car, but more picky on the 1991-93 non-turbos). Now it's up to you to change the thermostat (if necessary), and change the thermoswitch (if necessary) and clean the contacts on the relay and connector (do this anyway) so your car doesn't overheat and you don't have to deal with the head gasket.
To change the thermostat, drain enough engine coolant to get the level down below the thermostat- say a gallon or so. Do this out of the block drain, the radiator drain, or by pulling a hose off of the thermostat housing and catching as much as you can. Undo the two 12mm bolts holding the thermostat housing in place (you may need to slide the idle control valve out of its place) and remove the housing. Put the new 'stat and its seal in the same orientation.
To change the thermoswitch, drain the coolant as mentioned above or just unscrew the old one and catch what coolant you can, then quickly screw in the new 'switch and its seal.
Anytime you drain the coolant on your 900, you must open the bleeder screw (a twin fitting that sticks diagonally out of your thermostat housing) and then refill the coolant. Soon after coolant begins flowing out of the bleeder, close it again. This prevents pockets of trapped air in your cooling system.
Good luck! If you need any other help, post again.
Where do you get these parts? Look up the site sponsors, especially for the thermoswitch.
, Wed, 16 Nov 2005 18:28:13, Thu, 17 Nov 2005 15:50:36 <-- Viewing This Message
, Thu, 17 Nov 2005 06:40:05
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