When cold start no heat then while driving, gauge tops out then drops, but blows cold. When raise RPMs it drops down to normal, then repeats. Once it warms up, it's will blow warm shortly then back cold again. Top heater hose collapses at high rpms. Car over heats, prior to letting air out through the needle valve on stand pipe. Then at idle it seems to settle down. 1996 V-6 Buick Century Thanks in advance for any info you can give.

I think I answered this already, but just because you installed a new thermostat does not mean it is good. Sure sounds like a thermostat issue.

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.

Thermostat may not be working properly, hot coolant has to circulate via the heater core in order to get heat. Normally operation temperation should be 180 to 200 degrees.

Hi Dave the ECU receives messages from sensors, one of which is a temperature sensor. When the sensor responds to a temp higher than the normal operating temp the fans are then and only then supposed to operate. They will switch in for a brief period and then turn off again. The idle speed is in direct relation to the cold start up idle requirements and specifications. When the engine is cold the idle speed will automatically increase and as the engine achieves operating temp, the idle speed will decrease inthe way you have recorded. If you start the engine and allow it to idle until normal temp is achieved the fan should cut in. The way you've desribed all systems are A okay!. Regards John

Any chance of a head gasket leak? Is the coolant level still full? These were known for head gasket issues. Coolant is a closed system and level will not drop unless there is a leak. Make sure there is no air in the system. Replace the radiator cap to make sure that it is operating properly.

make sure you have plenty fluid in the radiator and the bottle. sounds like it is low.

It sounds like your thermostat is broken. The metal retaining tabs that hold the thermostat together can break over time. I would recommend pulling it out and checking it. When installing a thermostat there is an arrow on the edge. Make sure it points up. toward the top of the cylinder head.

Check to make sure your thermostat works right by monitoring the warming up of your engine. With a completely cold engine, start and run the engine for a few minutes, then put your hand on the top radiator hose to monitor if and when it gets warm as the thermostat opens more and more and note the gauge reading( if it works) the top radiator hose should be unbearably hot within 5-8 minutes. If the therm. opens right it should close right aswell, staying open a little while eventhough the radiator may have cooled may be what you are experiencing causing the rapid cooling and is nothing to worry about. The Hose should not get warm very soon after starting the engine. Regarding you gauge, lets take one step at a time, verify proper op. or the therm.

your head gaskets are bad.... This is a common plroblem wiht those symptoms.

Just finished fixing my daughters 1999 taurus heat. It would blow warm only when running down the road. At idle it blew cold. I started with replacing thermostat, and water pump because they are the easier fix. Still did not help. Then I replaced the heater core. A daunting job but not that hard to move the dash slighly out of the way to replace. There is a good write up at tarusclub.com. After that, heat was better but at idle, it would still blow cool sometimes. Researched and found answer. Park car on the steepest hill you can find with front of car up. Start car and take off reservoir cap. Let car warm up and keep rpms about 1500. After a while the fluid will come running out of the car and all over the place but it will bring air bubbles with it. Reduce rpm, add more fluid and repeat about 3 times. It will make a mess but after that, the heater works perfectly. We get heat long before the temp gage indicates any and it never blows cold unless you lower the temp.