Cooling Guru Needed !!
 

89 302 auto w/ 126k miles
no major modifications (K&N, 3:55, mufflers, timing advanced to 12 degrees but I always use 91 octane)
note: heating core is bypassed (damn thing leaks)

Temperature guage was reading about 220 F. So, I:
1.) Flushed the engine block with water.
2.) Changed thermostat to 180 F.
3.) Replaced coolant (50:50 mix).
4.) No leaks.

This didn't help. Guage was still reading 220 F. So, I:
1.) Replaced radiator cap.
2.) Replaced temperature sending unit.
3.) No leaks.

Guage read 200 F. Definite improvement, but it should read 180 F. Next, I measured the resistance of the temperature sending unit over a range of temperatures. Now, Ford says the unit ranges from 10 ohms (full, or 270 F) to 73 ohms (empty, or 130 F) which, assuming that scales linearly, allows one to calculate the expected temperature. Here are my results:

Resistance (ohms) Guage (F) Expected Temp (F)
65 150 148
48 180 186
43 185 197
42 195 199
41 200 201
36 205 215

These results tell me two things. 1.) My car is running hot, FOR REAL. 2.) My guage is slightly off. (Also, my guage always showed some sort of erradic behavior - bouncing from 160 F to 220 F to 195 F to all over the place - especially after driving on the highway or flooring the accelerator).

Anyways, I need some help on what to do next (before I buy a new radiator). Here are some specific questions:

1.) Does the temperature sending unit's resistance scale linearly with resistance?
2.) Is there some trade secret to changing coolant? (Like clever ways to purge air?) I just drained the system, flushed, and then filled it back up with coolant.
3.) Is it worth scouting for a new guage for my instrument cluster?
4.) WHY IS MY CAR STILL RUNNING HOT!?

Thanks for all your input. I would really, REALLY like to solve this problem. It is driving me insane.

Evil Joe

First off, I would run a 70/30, water antifreeze mix.

Second, I would get an autometer temp gauge or something of equal quality. The stock gauges are not always the most accurate thing to go by.

Third, with a 126k miles on the car, it could be that the stock radiator has seen better days. I would have it pressure tested to see if you have a small coolant leak. Or even better get a nice 3 core radiator.

I agree that a 50:50 mix is too much antifreeze even for the winter.

I also suggest getting a bottle of redline water wetter.

Do yourself a favor and duble check your timing, if it is advanced too much it will cuase the engine to run hot.

I took some of your suggestions and made a few changes to my cooling system:

1.) Drained coolant (50:50).
2.) Refilled with a 75:25 (water:antifreeze) mix.
3.) Added 1 bottle of Water Wetter.
4.) Ran for 30 min on a level surface with the cap off to purge air.
5.) Refilled as needed. No leaks.

No change. ******!! The car still runs at about 205 F even though there is a 180 F thermostat in there.

Looks like I'll be buying a new radiator. I seen on Ebay some (unspecified brand) 3-core radiators for about $130. Anyone know if they are any good? If not, what would you suggest?

Thanks,

Evil Joe

Quit fighting the small stuff. Remove the radiator and have it profesionally serviced, or replace it.

the motorsport aluminum radiator (I think it is part M8005C, but don't hold me to it) is a good piece if you don't mind plastic side tanks. I haev been running it on my car with an Edelbrock pump, silicone hoses all around, hp 180 thermo, and flex a lite 175 black magic fan for years now without problems. Ideally, you want welded aluminum tanks on your radiator, but that will cost more. There are many makers out there with all aluminum offerings and Fluidyne is one of them. Either way, check out Summit or Mustangs Unlimited for ideas.

Does your engine cool off at all when you're driving highway speeds compared to at a stop or does it do the opposite, or does the temp stay the same no matter what?

You could also pull off the water pump (gaskets really aren't that expensive) and make sure that the impeller is still intact and that it is actually flowing coolant.

How do your radiator hoses feel? If the bottom one is cold and top one lukewarm there's probably a flow problem somewhere in your cooling system, probably your radiator or corroded water pump impeller, hopefully not a rust blockage or something in the engine.

One thing you could do just to see if your radiator may be plugged is to take off both hoses and run water through the top and see if an equal amount comes out the bottom, or if it flies back out the top again. I had a radiator blockage when i had an 84 5.0L and i'd pull the bottom hose and it would only allow a fair amount of coolant to escape, just enough coolant to keep the engine from going nuclear, when i'd fill the top hose it would run out the top.

Good luck, hope some of this helped in some way.

first before you buy anything else, is get an accurate gauge. if you are going by the stock gauge, forget it. its like measuring bore and stroke with a tape measure!

Get an Autometer gauge in first or use a buddies Infared thermometer then go from there. stop buying parts until you get and ACCURATE READING! you may have been running at perfect temperature to begin with and didnt realize it with the crappy stock gauge.