questions about cooling system operation
 

I replaced my thermostat this weekend ($10 Lowes snap-ring tool with pins bent inward for grip) and the car is running hot. I a, bleeding and bleeding everytime it sits I get a little more air out of the bleed screw. My question concerns the operation/capacity of the colling system:

1) Do the lower covers/pan have to be on for the system to cool properly?

2) should the system cool properly without the fans or are they essential to maintaining proper temp, even when the car is moving?

3) Besides bleeding through the bleed screw, is there another way to get coolant into the chamber where the thermostat is located? On other cars I have owned (diesel benzes for example), I always had to actually put water into the coolant hoses on both sides so that the thermostat would open. without coolant touching the thermostat, it won't open, no matter how hot the engine gets.

I'm not sure about the lower pan but it shouldn't affect cooling air flow to the radiator noticably.

The fans are used for city traffic driving. When sitting at idle or going slow there is not enough airflow over the radiator for proper cooling. If you are moving moving over about 15-20 mph then the radiator should cool without the fans.

I've filled my coolant several times and I never had a problem with air pockets. The best way is to use a coolant system pressure tester to pressureize the system then crack the bleed screw until there is no more air coming out. You can do this by blowing into the the coolant reservoir but that tastes bad and is less effective than the press tester.

If you think you still have air in the system, run the engine until it reaches normal temp. Shut it down and let cool! Then bleed it again.

If you still have a problem then it might be something else, like my clogged radiator.

Thanks for the info. I've bled and bled this thing and it gets a little better each time but it still goes up to the top white mark when I'm sitting still before the fan kicks in. I think its time for some radiator work...lower temp thermostat and fan switch would cure it for now but it seems like a band aid.

I had the exact same problem when i changed my thermostat. Raise the front end of the car at least a foot when you bleed the system (park it on a hill).

If that doesn't work, throw a bottle of water wetter in the system. This was the cure for me. Dropped the gauge reading at least 3/4 of a point.

I was told by the guys at huntley racing that they could sell me a low-temp thermostat, but they reccomended that i not use it if i could find any other way around the problem. They have had occasional problems where the head really never comes up to proper operating temperature with the low-temp thermostat installed. The low-temp thermostat is really for running in extreme climates.

Mike

together they make the fans come on at a lower water temp but you need both.

my fan comes on just above the 1st mark. only using one fan because of a bad bearing and is unplugged.

the a/c doesn't work and isn't needed.

Had the same problem with my '87 NA. Radiator was clogged.

Your stated "it still goes up to the top white mark when I'm sitting still before the fan kicks in."

If the temp goes to the top mark before the fans kick on only when you are sitting still then you need a new thermo switch (located on the driver's side of the radiator). The stock switch kicks the fans on about the 3/4 mark and the aftermarket cooler switch kicks them on at about the 1/2 mark.

This is not indicative of air in the system. Air in the system will cause overheating at ALL speeds.

If you get overheating at all speeds then let it heat up to normal temps, turn off the engine, DISCONNECT THE FAN ELECTRIC PLUGS, and feel the radiator at several different places. It should all be hot. Half of my clogged radiator was cold and half hot. A new radiator later and my baby's cooling system ran like new.

lower pans not needed for cooling

have mine in lay-up for winter put recently idled for an hour

In 50 deg weather, from cold, my car runs appx 10-15 minutes, no fans.

Then low speed on driver's fan kicks in, about 5 minutes later both fans to high speed. Then shortly after, high speed off, slow speed on briefly until it shuts off. And it starts over again...

Never went above 1/2 way on gauge.
Normal operation should be no fan until thermoswitch in radiator turns on. Another 5-10 deg increase and the other thermoswitch in AC controls closes. This bypasses slow speed resistor in driver's side fan, it goes to high speed. This thermoswitch also enables passenger side fan, whether AC is on or off.

This 2 fan, and 2 speed on driver's fan circuit should keep that temp needle steady at mid-point. Mine may run a tad cooler as I installed turbo pump and lower temp switch.

I concur your radiator may have some blockage

I went out to my mechanic's place yesterday and he went over the car as much as he could without removing hoses and such. Using his pyrometer (is that the right word), we deduced that there is a flow problem somewhere, the question is where. The lower hose is not heating up as much as it should (leaning towards thermostat or, worse, broken water pump). We were not able to get a clean shot at the radiator so we could not measure temp differences. Pressure in the hoses seemed good and nothing was really hot, making the diagnosis tricky. I'm going to replace the thermostat tonight in case it is defective and test the water pump by turning the engine over with the return hose disconnected to see if it moves water.