I changed the coolant and now it's running so hot that I can only go a few miles before I have to stop and let it cool off. It was OK before I changed the coolant. I used the proper orange type and I bled the air from the two bleed spots. If it's suddenly a bad thermostat, it looks as if it's going to be pretty difficult to replace. Thanks, Jerry

No your car will not overheat, but it is advisable to my 50% coolant on the water to prevent deposits of rust and other debris that may affect the effectiveness of the cooling system.

This can be caused by an insufficient coolant (aka antifreeze) level. Look at the coolant level in the reservoir under the hood. There should be two marks on the bottle "warm" or "hot" and "cool" or "cold". If the engine has been running for a while as in the case when the car has been driven few miles, the coolant level should be up to the "warm" or "hot" line on the bottle. If the car has been parked without the engine running for a couple of hours or more, the coolant level should be at the "cool" or "cold" line on the bottle.

Never remove the radiator cap when hot or if the engine has only been been stopped for less than 2 or 3 hours.

If the hot coolant is at a level that is below the warm or hot line, you should add more of the coolant / water mixture only to the reservoir - not to the radiator. If you are only able to check the coolant level when it is hot - you will have to repeat this procedure until the coolant level of the reservoir is maintained. Checking the hot coolant level can only be done when it has been allowed to cool between hot checks. The cooling period is the only time when coolant is drawn from the reservoir back into the radiator.

If the cold coolant is at a level below the cool or cold line of the reservoir you should add more of the coolant / water mixture to the reservoir and to the radiator, too. Fill the radiator to the top of the neck where the tube from the reservoir connects to it.

If you're still having widely fluctuating temperatures while driving at normal operating speeds, there may be a problem with the water pump, thermostat or other portion of the cooling system.

I hope this helps & good luck!

CHECK COOLANT LEVEL STILL LOW.ADD MORE COOLANT.UNTIL RADIATOR OVERFLOW FULL AT COLD MARK.THEN CRANK ENGINE UP LET IDLE FEW MINUTES LOOK DOWN COOLANT OVER FLOW JUG ADD MORE COOLANT IF LEVEL DROPPED.WHILE ENGINE RUNNING KEEP EYE ON TEMPERATURE GAUGE.WHEN THERMOSTAT HOSE GET HOT.TURN OFF ENGINE WAIT A LITTLE WHILE TO KEEP FROM GETTING SCALD TAKE LARGE RAG PLACE OVER OVERFLOW JUG RADIATOR CAP.OPEN CAP A LITTLE A TIME.IF COOLANT TRIES BOIL OUT.LET VECHICLE SET A WHILE LONGER.ADD MORE COOLANT.WHEN COOLANT LEVEL CORRECT AND ALL AIR OUT THE COOLANT SYSTEM.IT WILL STOP OVERHEATING.LONG AS ENGINE RUNNING HOT TURN OFF THE ENGINE POUR IN MORE COOLANT UNTIL COOLANT LEVEL STOP DROPPING IN RADIATOR.KEEP COOLANT LEVEL IN OVERFLOW AT COLD MARK.DONT OVER FILL OVERFLOW JUG.

The temperature sensor is unservicable..........Hope this helps.

bad thermostat and coolant maybe low. when a engine gets to hot at certain boiling point it evaporates

1998 Audi A6 2.8

It could be that the thermostat is stuck in the open position thus providing maximum coolant flow through the engine when the engine is still cold, ie from a cold start. (The thermo should close when the engine is stopped and cold and it opens up once the coolant temp increases and the engine has been running for a few minutes.) Once the engine is hot maximum coolant flow between engine and radiator is normal.

Do you also find that your heater takes a while to provide warm air to the cabin in winter when you notice this condition?

If you do not know when the thermostat was last changed then I would suggest you change it. ( If it malfunctions and sticks in the closed position you will really have a problem). The radiator/engine coolant could no doubt do with a flush and change in any event as it should be done every 2 years. If you don't know when it was last done - do it. Cooling systems tend to be a neglected part of essential vehicle maintenance.

Cheers
Sean
Voluntary contributor.

When the car is completely cool,check the electric fan(s) for smooth rotation.

Clean/check/change the thermo sensor,contact and wire.

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Excavate air pocket in coolant system / check for head gasket leak

This test will kill two birds with one stone.

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MAKE SURE THE COOLANT SYSTEM and ENGINE IS COLD!

RAN THIS TEST IN A WELL VENTILATED AREA ONLY!

You will spill some coolant during this air pocket purge test.......BE KIND TO THE ENVIRONMENT and ANIMAL please clean up after the test!

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Put the front end on a pair of ramp or park your car on a VERY STEEP HILL (radiator facing top of the hill) .

Top of the coolant reserve tank

Let it ran for 10-15 minutes.

Monitor for air pockets escaping from coolant reserve tank.

Small amount of bubbles is OK at 1-5 minute mark

After the thermostat open up (after 195 F warm up) at
5-12 minute mark or after high idle you should see less bubbles.

If you do not see any in rush of bubbles then your thermostat may be partially stuck or rusted badly inside the thermostat hosing.

Give the thermostat host few gentle taps.

If you see larger bubbles surfacing after 15 minutes then should do a hydrocarbon (HC) dye test to test for potential head gasket leak.

Let engine cold down and top off coolant reserve tank.

Start monitor for coolant lost

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A coolant flush is require every 2 years or 24,000 miles.

I recommend the thermostat that has a relief pop-let to reduce the change of burst radiator and coolant hoses.

Make sure you get a new thermostat gasket,black RTV and fresh coolant for the job.

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replace that thermostat again...flush radiator any way...then see how it runs...

Check your thermostat is working properly and maybe even flush and replace coolant. Good luck and have a great day.

check and see if you get water/coolant circulates when you have the cap off (only check from cold start) the original water pump came with a plastic impeller and tends to strip on the shaft also check your thermostat before replacing water pump.