Engine Need help with cooling system issue

germain101

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Feb 24, 2013
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So I’ve been dealing with an odd problem with my mustang. It started a few months back when I took the car for a little spin around the neighborhood. It probably hadn’t been driven for a few months before this. While I was cruising around, I noticed the temp gauge getting up to around to the ¾ mark. I imminently went back home and parked it in the garage. The coolant level was good but the coolant looked a little old (yellowish not bright green). I changed out the fluid, thermostat (180*) and radiator cap (16 psi), all for good measures. I worked all of the air out of the system and took the car for a spin around the block. Started doing the same thing! I pulled back into the driveway, but this time I let the car idle to see if the temp would go back down and it did.I bought a block tester to see if there were any hydrocarbons in the coolant and it gave sort of inconclusive results. I then decided to just put a new set of head gaskets on the car, along with a new water pump. Well, I get the car all back together and I’m still having the same problem. The car has a newer dual core radiator and I am not running any underdrive pullies. I’m also not running any electric fans. I don’t know if maybe the temp gauge sending unit is bad? I’m just driving around the neighborhood at like 20 mph in 2nd or 3rd gear and the gauge will slowly creep up to about ¾ in about 5-6 minutes of driving. I burped the system with the car jacked up on the front drivers side with the heat on high and the cap off for 30 minutes or so. I suppose I could try to burp it again with one of those special funnels, but I’ve done it so many times in the past and have never had any problems. Anyway, if anyone has any ideas, I would really appreciate the input.
 
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Feb 26, 2018
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In my experience overheating when driving and not overheating when idling is a sign of a weak fan clutch. Spin it with your hand with the engine out see if it has an resistance. That's where I would start.
 
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germain101

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Feb 24, 2013
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In my experience overheating when driving and not overheating when idling is a sign of a weak fan clutch. Spin it with your hand with the engine out see if it has an resistance. That's where I would start.

I appreciate the reply! I figured the fan clutch would be doing most of the work while the car was idling and, being that my temps would go down at idle, it must be good. But it didn't occur to me that RPM plays a role in the function as well and maybe its not functioning well above a certain RPM. It doesn't necessarily spin freely, but there isn't a lot of resistance either. Maybe its just enough to function at idle, but at low speed with a load on the engine, it doesn't have enough resistance to engage. I ordered one this morning, so we'll see if that does the trick.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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Install a mechanical gauge, even if you zip tie it to the wiper arm temporarily and get an actual reading you can compare to where the gauge is reading on the 'normal' sweep
 

Boostedpimp

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encase you ever wondered
 

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germain101

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Feb 24, 2013
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encase you ever wondered

That sort of leads me to believe that the gauge is working correctly as when I was burping the system, the gauge stayed between the "A" and "M" (car is a 93) and I have a 180* thermostat. While driving, it would get up between the "O" and "R". Fan clutch should be here tomorrow, so we'll see if that does the trick. If not I'll put a mechanical gauge on there and see if there is any deviation from the factory gauge. Thanks for all the responses!
 

germain101

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Feb 24, 2013
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UPDATE:

Christmas came early and I received my new fan clutch today. First thing I noticed was that the shaft was much stiffer to turn than the old one and after being installed, there was a significant audible difference as well (the sound of much more air moving with an increase in engine RPMs). I let the car warm up in the driveway until the thermostat opened and then took it for a spin. The temp gauge never even made it to the half way mark. It stayed in the bottom half the entire time I drove around and it seemed like the A/C was even blowing colder. The old fan clutch must have had just enough resistance to allow it to cool the car while at a very low RPM, but when driving at low speed with a load on the engine and very little air flow over the radiator, it didn't have enough bite to pull the necessary air flow. Anyway, many thanks for everyone's input, it was much appreciated.
 
Feb 26, 2018
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Glad it worked out for you, I have worked in a Ford dealership for almost 30 year, and have replace a ton on fan clutches for that problem .
 
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