the sound of water under the dash

[LethalGT]

Hey guys hope i can get some help. I recently bought an 1989 Chevy Silverado with the 350 V8. The truck runs great and only has 93,000 original miles! My question is I can hear water swishing under the dash close to where the glove box is. Anyone know what it is? Also The temp gauge will normally stay about 210 degrees, but occasionally it will rise between 210 & 260, roughly 245 degrees and will stay there for just minute or so before dropping back down to 210. Usually the service engine soon light comes on by this time also. What is the normal operating temp & could my water sound and the rising temp go hand and hand? Do I need to change the thermostat? Any help is greatly appreciated, Thanks, Mike.

[jdfson]

Sounds like there is air in the system. Normal operating temp is usually 190 to 210. I would suggest replacing the t-stat with an OEM temp which I believe is 190. Make sure tou have good waterpump action and the rest of the cooling system is in good shape. Good Luck!

[LethalGT]

Is air in the system a bad thing? I think im going to go ahead and change the thermostat just to be safe. Thanks for the info....

[acemech129]

Actually the stock thermostat is 195 degrees not 190, your problem sounds like the coolant level is low in the radiator, check this and if it is check for a leak, also had this noise caused by deposits in the heater core, if coolant isnt low backflush heater core and refill system. To back flush heater core remove hose from radiator that goes to heater core and remove other hose at heater core, hook garden hose to hose from radiator to heater core and turn hose on this will flush deposits from core, hope this helps.

[LethalGT]

Thanks for the reply. I checked coolant level and it is fine, so it could be deposits in the heater core. I'm gonna get a thermostat today and I will also try backflushing the heater core. Thanks for the help!

[Tercel GTS]

you better check the drain for the a/c condensor tray, sounds like the drain is stopped and the tray is full of water, expect wet carpet soon

[LethalGT]

I replaced the thermostat and it runs right where its supposed to now and just in time, we hit 104 degrees today in oklahoma. I havent heard the sound of water under the dash since I replaced the thermostat, maybe it cured it. I appreciate everyones input.