Temp Gauge with a Mind of its Own

[94VL]

1994 VL,the temp gauge stays steady when warming up,but when it reaches operating temp it has a nasty habit.It will drop rapidly about 1/4 gauge,then slowly creep back up to the operating temp it read before it dropped.It will continue this over and over again.I replaced the temp sensor with no change.I'm guessing a faulty gauge....but I cant be sure.

[deadBird]

Make sure the voltage going to it stays at 5v.

[BlazerLT]

Originally Posted by 94VL

1994 VL,the temp gauge stays steady when warming up,but when it reaches operating temp it has a nasty habit.It will drop rapidly about 1/4 gauge,then slowly creep back up to the operating temp it read before it dropped.It will continue this over and over again.I replaced the temp sensor with no change.I'm guessing a faulty gauge....but I cant be sure.

Is this when the engine is idling and you are sitting still?

If so, this is normal.

Just after the 1/2 mark the engine fan turns on until it cools it down to between 1/4 to 1/2 and then it shuts off until the coolant temperature heats up again.

This is what happens when you have a transversely mouned engine with no direct fan pushing air through the rad all the time.

I own a 1994 VL and this is what mine does and it is completely normal.

[94VL]

This happens when driving.It hunts between 1/4 and 1/2.It never exceeds 1/2 gauge.I'm thinking the thermostat is acting up (opening and closing repeatedly),but I'm not sure.Only 35,000 miles.

[BlazerLT]

When is the last time you serviced the cooling system?

From what you have said, I would think you should replace the thermostat, flush and refill your cooling system and look to see if the cooling fan is coming on when driving on the highway. (Which it shouldn't)

[94VL]

Radiator new 1-1/2 years back,system flushed and coolant replaced at the same time.Engine has never overheated and never run past 1/2 gauge.I dont believe I ever remember the fan coming on,even in the heat of summer.

[BlazerLT]

Originally Posted by 94VL

Radiator new 1-1/2 years back,system flushed and coolant replaced at the same time.Engine has never overheated and never run past 1/2 gauge.I dont believe I ever remember the fan coming on,even in the heat of summer.

Replace the thermostat.

The fan will indeed come on if you still in one place and let it idle.

[OverAllComa]

Yeah, I know what you're talking about. See, Blazer, I'm pretty sure he's talking about going between 1/2 and 1/4 within a split second. I had the same problem in my old Z24. I can say that I changed the thermostat and it still did it occasionally. The only other idea I had was a bad sending unit.

Sorry, not much help, but you're not alone in the problem.

[94VL]

It will go down faster than it goes up.But it never goes past 1/2 way (normal operating temp)upward.Its like a wire gets disconnected when it reaches 1/2 way and then gets plugged back in at 1/4.The new sensor does the same thing as the 1994 original one.

[BlazerLT]

Originally Posted by 94VL

It will go down faster than it goes up.But it never goes past 1/2 way (normal operating temp)upward.Its like a wire gets disconnected when it reaches 1/2 way and then gets plugged back in at 1/4.The new sensor does the same thing as the 1994 original one.

What you are seeing is a thermostat sticking closed, slowly heating up the engine, then opening up and quickly cooling the engine with a burst of coolant flow.

Then the thermostat will close again.

Sounds like the thermostat bro, it is starting to stick. If it sticks closed for good, good bye engine.

[toyoman28]

My 94 cav is doing the same thing with temp gauge. Up to 1/2, dwn to 1/4. I replaced the thermostat thinkning that would cure it but no good. It still cycles although not quite as much, but still the same pattern. New radiator also and was thinking about the sending unit till I read this. I guess I'll save the money and just watch the needle do it's dance. Car never overheats and fan comes on fine to cool.