Hi.Water temp gauge in dash board drops off normal temp down to bottom of gauge then back up again. My water levels are fine car is not over heating. What could be the problem please. John.

You have to make sure the thermostat is working properly and is the correct one. Idle the vehicle for about 20 minutes and then feel the upper radiator hose. It should be hot to the touch. Drive the vehicle and when the temp gauge falls to 'cold' stop and feel it again. If it is much cooler to the touch than before the thermostat is defective or wrong.

This may be an electrical issue in the dash and a phantom problem. I would suggest measuring the water temperature in the radiator to see if it matches the guage (normal temperature should be around 90decC. Higher revs would increase water flow via the water pump not lower it so I am thinking some kind of restriction - check your radiator fins are not blocked there could be blockages in the radiator or less likely in the block valleys, other things to check are that your hoses are in good condition and they don't flatten with heat. A faulty thermostat is also possible.

you may have a bad engine fan, head gasket issue or thermostat issue. best to have a shop check it out.

Its fine, temp needle going up shows that engine is warming up and as soon as the radiator fan starts, temp of coolant drop and this is shown by the temp gauge needle. In most cars (even mine) it stays in middle most of the time unless you are in a traffic with AC on, it will show up more temp. What you can do is get the radiator flushed and coolant changed. Also check the water pump. To do so when engine is cold (in first start in morning), open the radiator cap and ask someone to rev the engine. If the coolant level moves up and down then water pump is also fine.

The air needs purged from the system. the mechanic should have done this. Any way remove the radiator cap ,start the car, Have some coolant ready to pour in. As the car starts to warm up it is going to push some coolant out.when this starts rev the engine up some , this will draw the coolant back down.add some coolant keep the engine revved up. at some point you will notice the the level drops alot this is the air getting to the radiator. Add more coolant. install the cap. It takes higher rpm's to push the air threw the system. You might do this a couple of times. but this is the fastest way I have found to purge air locks in the heater core( no heat). Keep a check on the coolant level in the resevoir. because if this gets to low it will **** air again.

Hi, the likely problem is a bubble forming in the system, possibly due to a head gasket failure.

Try stopping on a steep incline--does the heater stay warm? If yes, what you have is an air bubble that hangs at the heater hose until pressure from the water pump blows thru it as the engine speeds up. Park on an incline, open the radiator cap, run the engine until the thermostat is open, turn the heater on, crack open any/all bleed ports to release any trapped air, and fill the radiator to the neck. Wait until the level stops dropping and make sure bubbles don't continue to come up. If they do, you may have a blown head gasket that will keep forming these bubbles until you change the gasket.

If your temp gauge on the dash never gets to operating temp your thermostat is stuck open and needs to be replaced.

is the temp gauge sender new
or the engine cooling fans spinning fast enough
air in the heating pipes ? bleeding

With engine cold, remove rad cap & check level in rad. Top it up if needed to 1 or 2 inches from top. Start engine, turn heater on (not defrost) and observe coolant level as engine warms up, add if necessary. Radiator fan should be off, and only come on when engine reaches normal operating temperature, for a short time, then shut off again. Let it run until that happens about 3 times, then put rad cap back on. If temperature gauge climbs up over normal toward hot, too much, shut it off. Do you now have heat? Is rad fan acting as I described? Let me know.

Hi there iask,

I could call myself ianswer. My name is Mike. I've got a 91 wrangler that used to do the same thing.

With me it was an air pocket. The temp sensor responds to a heavy medium like water, not air. As an air pocket circulates and comes into contact with the sensor, your gauge will fluctuate.

I'm sure you checked the coolant levels already, but hear me out. What I'm suggesting is like chicken soup, it can't hurt, it can only help.

Just because a radiator looks full, doesn't mean it is. Air pockets can exist in the engine and heater core. We're going to get rid of any.

Checking the coolant level.

• I know, you've been there, but I say this to everyone. First and foremost: BE SAFE!!! Wear safety glasses.
  
• This should be done with the engine cool. Never open the coolant caps on a hot engine.
  
• When you look in the radiator, do it from an angle, not directly in front.
  
• Have a hose or a couple two liter bottles full of water available.
• Take off the radiator cap. (Do not take off if engine is hot)
  
• Is the water level low? If so, top it off.
  
• Make sure the transmission is in either PARK or Neutral and set the parking brake.
• Start the engine, put he HEATER and FAN on HIGH. Go back to the radiator..
• Observe the water level in the radiator. If it drops, top it off again.
  
• At first it should do nothing. The water will seem to just sit there. This is normal. The water in the engine is still cool. The thermostat is closed. As the water in the engine heats up, the thermostat will begin to open. When it does, you will notice the water level begin to surge up and down.
• When the thermostat finally opens all the way, the water will start moving as it cycles through the system. You will be able to tell when this happens.
• Does the water level drop at this point? If so, top it off while it's circulating. Adding water will close the thermostat. Be prepared to wait through the cycling two or three times until the water level remains constant during a cycling.
• Make sure the heater is blowing hot air. Turn it off. wait a full cycle. Then turn it back on. Check another cycle for level drop.
  
• When you don't need to add water any more, put the cap back on. Observe the temp gauge. Has it leveled off? If so, it was an air bubble and it's gone. If not, We go to phase 2.
  

Either way, let me know how it goes. If you have any other problems, click the ASK button.

Remember: Good things come to those who Rate.

Mike