Coolant System Pressure Switch
11-25-2018, 01:59 PM
#1
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Location: Memphis, TN 1987 S4
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Coolant System Pressure Switch
my 89 S4 is loosing coolant from pressure switch. Just changed the expansion tank. Is there a reason coolant going towards the switch instead of out the overflow? I didn’t have a leak there before the tank change. I went with the metal tank. Does it create more pressure than plastic one?
11-25-2018, 02:32 PM
#2
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my 89 S4 is loosing coolant from pressure switch. Just changed the expansion tank. Is there a reason coolant going towards the switch instead of out the overflow? I didn’t have a leak there before the tank change. I went with the metal tank. Does it create more pressure than plastic one?
11-25-2018, 03:59 PM
#5
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I used it because I had it handy and it pushed into the hose tightly even so I used a clamp. It is also inert to the coolant but so is aluminium and plastic [the switch itself is made of some kind of plastic]- it is a low pressure service at the end of the day.
11-25-2018, 05:14 PM
#7
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Mine has not indicated anything amiss and the posts I saw on the subject did not indicate any issue. I have seen the logic described in a post but for the life in me I cannot remember the details.
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11-26-2018, 11:07 AM
#8
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If I recall correctly, its function is to preserve a temporary low coolant indication, for instance if it's a touch low, the light will come on, and without the pressure switch it can turn off if the car heats up and the level in the tank rises. When it's all present and working correctly, once the light comes on it will stay on until the pressure sensor detects a release of pressure, eg like you've opened the cap and added coolant.
I suspect it's just an open or closed condition on that switch, so if it triggers a warning with the connection left open, you could jumper it closed. I'm not sure which way it works, hopefully someone else can confirm.
I suspect it's just an open or closed condition on that switch, so if it triggers a warning with the connection left open, you could jumper it closed. I'm not sure which way it works, hopefully someone else can confirm.
11-26-2018, 03:55 PM
#9
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The vent hoses that include the pressure switch are 8mm ID hose, and can be easily replaced completely with 8mm or 5/16" fuel hose. This is standard (not fuel injection) hose, so it can make the bend at the vent nipple on the radiator. Replacing the hose gains you a) new hose, and b) avoids needing that tubing and the two extra opportunities for leaks that a clamped-in bit of metal tubing offers. The fuel hose is readily available locally, and inexpensive. I painted over the white markings on it with a -gasp- black felt marker.
At some point I'll get the factory hoses to go there. They weren't available when I last decided to renew all the cooling system hose sections.
At some point I'll get the factory hoses to go there. They weren't available when I last decided to renew all the cooling system hose sections.