coolant temp drops when heater on

[prybylo]

I have a 2000 V6. My problem is that when I have the heat on the coolant temp never stabilizes. It oscillates between cold and normal. Worse now that air temp is below zero. Without the heat on the coolant temp is rock solid.

It's still under warranty and two trips to the dealer haven't fixed it. The first time they fixed a "loose wire", the second time replaced the thermostat. The thermostat helped but didn't fix the problem.

I've noticed that the engine fan runs immediately even when engine is cold so I suspect a bad fan clutch. Alternatively, the temp swings could be normal - after all I'm taking heat out of the coolant when using the heater.

Is the fan supposed to spin when engine is cold? Other ideas?

Thanks

 

[yob_yeknom]

No answer to your problem, but the fan always spins.

 

[FordSploderXLT]

Does the heat get colder when the collant temp drops, if not, coolant naturally gets colder when the heat is on.......thats why you turn the heat on to prevent overheating........

 

[prybylo]

The heat does drop when the coolant temp drops. The first winter I had it the heat was very strong, but since this problem the temperature of the heat is not as high.

 

[BradE.]

If it happens at higher RPM that is somewhat normal. The water pump is pushing more coolant, so it probably will drop a bit. When I go above 3000 RPM off the line my gauge drops a touch also. It goes right back though and all is well.

Your problem just sounds like a weak thermostat, since your losing heat when the temp drops. Change it, use a 192 degree unit. They cost about $5 and take less than 30 minutes to install.

 

[prybylo]

Mine oscillates even if I'm driving at a steady speed, 40 mph or 70 mph, doesn't matter. But only with the heat on

 

[BradE.]

Time for a new thermostat then. You might also want to pick up a new radiator cap also. Make sure to bleed the cooling system when you are done to remove any air from the lines.

 

[prybylo]

The dealer replaced the thermostat - still under warranty. I replaced the radiator cap. The thermostat helped but didn't fix this.

I've thought about air in the lines. Whats the best way to bleed?

 

[BradE.]

The thermostat still could be faulty. Motorcraft thermostats are JUNK! I went through 3 thermostats from NAPA before I got one that worked.

The best way to bleed the system is to back the radiator cap off one notch so that it's on but loose. Start the truck and run it at 2,000 RPM for 5 minutes. Shut it off and top off the radiator (if there was air in it the level has droped). Then restart the truck and with the heat on the highest setting run the truck at 1,500-2,000 RPM until the thermostat opens. (can take up to 15-20 minutes). After it opens top off the radiator and close the cap. Presto, you're done. Check the coolant level the next day and top off radiator and recovery as needed.

 

[tcbarney]

There's a huge long thread on this forum somewhere about oscillating coolant temperature. A lot of potential fixes suggested. Me, I'm beginning to think it's just a "feature."

Mine does it, too. I don't think it matters if the heat is on or not.

But I've recently discovered a leak in my Heater Control Valve that I've yet to fix. Will be interesting to see if that helps the problem. (It's letting coolant out, so it could be letting air in.)

 

[Texan01]

The heater acts like a mini radiator so the engine will run a bit cooler than normal. the t-stat is cycling between open and shut.

The engine fan is driven off the water pump by a thermostatic clutch that regulates fan speed based on temperature and engine speed, if the clutch is good it'll spin for a while cold and then slow down after you rev it up past 2500 rpm, the fan is goverened to about 3000 rpm maximum (under full hot condition like in the middle of a 110 degree summer and the A/C is on)

Here's a trick I did for my Chevelle to keep it hot during the winter, put a piece of cardboard over half of the radiator. since it was slow to warm up even in 40 degree weather it took 10 minutes to get it hot.

Mine will stay steady with the heat on, but if you have to stand on the gas it'll get hotter.

 

[Tango40]

My buddy at work had the same problem on his 2001 today we

finnally thought about the radiator cap and thats what it was,it was not sealling,bought a new one solved his problem.hope this helps.