What is wrong when my 1998 Oldsmobile Van suddenly has the temp gauge peaking then lowering - back and forth based on turns and when I hit the gas. Then when I got home, I opened the hood thinking it needed anti-freeze, but there was this LOUD hissing sound coming from the big hose on the right hand side? Thermostat issues or worse?
Cars & Trucks - Oldsmobile - Silhouette - 1999 Oldsmobile Silhouette
Answers & Comments
You are probably low on coolant. When there is air against the temperature sensor, it will read cool even when hot, because air won't conduct the termperature to the sensor. This explains why turn slosh would make it work for a bit. Hissing is very bad. That not only means hot, but leak. You can't drive a car with leaks. If you need to drive it to a shop, wait for it to cool, then add as much coolant as it wants. Then leave the cap loose. This will prevent pressure that can blow out all the coolant, but it is not a permanent cure. Water will slowly boil away, so is only a short distance patch. If you can tell were the coolant got lost to, you may be able to fix it yourself. But once over heated, you need to change the thermostat. If you can't find a leak, then rent/borrow a radiator pressure pump. Pump it up to a little more then the cap is rated for, and you will probably see the leak. If you don't, and if the pressure does not hold (slowly leaks down), then you probably have a bad head gasket. Hope not, because that is more like $600.
The heat gauge going up about half way is not bad.
They usually design temp gauges so that the middle is normal.
The fact it only take a few minutes is not necessarily bad either, because the thermostat is designed to heat up the engine as fast as possible. It does not allow any water to pass until the engine is completely up to temperature.
The varying with right and left turns has me sort of puzzled, but the only thing I can think of is low on water again.
And that is not impossible, since when you change hoses and thermostat, sometime air gets trapped in pockets. Those pockets work their way up eventually. So now you need to check coolant level again. This is always a good idea anytime any coolant is lost. Some cars need to be burped like this 2 or 3 times.
Another remote possibility is that the gauge suddenly decided to also go bad. Since it has the turning needle, it could be susceptible to centrifugal force I suppose.
But most likely is that now you are just paying so much more attention to the gauge that you are noticing every little thing that it may have always done but gone unnoticed before. I hope so.
You probably have lost considerable antifreeze through a hole in the radiator hose where you hear the hissing. Replace any hoses that have deteriorated to the point of failure or near failure including the heater hoses. Replace the lost antifreeze. Hope this helps!
About the only thing I would add is to make sure that the overflow/expansion tank is about 1/3 full of 50:50 antifreeze/water mixture (there should be a mark on the tank) when the engine is cold. Also, inspect the radiator cap seal condition (when the engine is cold).
Usually, gauge needles are damped enough that they don't respond to minute variations (like the fuel gauge and sloshing fuel in the tank). As kirkx has said: give it time to work out the air bubbles. The important thing is for the gauge not to be going into the red part of the scale. If this problem continues for weeks, you might want to have the cooling system tested for combustion products (leaking head gasket?). Good luck!