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FFCobra Craftsman
2,076 Posts
Discussion Starter · #1 ·
I need to know how the stock temp sensor and gauge works. It looks like when I first turn the key to "on" it will quickly rise to max, like some kind of diagnostic test. Then once I start the car it will actually drop back to the bottom and slowly rise, what's bothering me is how fast it's rising. No more than a couple minutes and it's maxed. I think it takes longer that this right? What I need to know is why. Is it actually that hot? Do I still have air or something in the system? Is the sensor at the manifold bad?

The block does heat up first, then the radiator slowly warms... but I can still touch the heater rails and sensor fitting after the temp gauge has hit 270.

I'm only concerned that playing around trying to fix this could damage my engine if somehow it is actually heating up that fast.

I'm running an aluminum crank rotation water pump (crown vic if I remember) with only the alternator and crank pulleys.

1,783 Posts
I'm no expert on the subject but the possibility that you still have air in the system would be a good place to start. Next may check the temp with some kind of thermometer and see if the gauge is true. At any rate good luck.

1,969 Posts
I'm not saying that you have the same problem but you may find my troubleshooting process interesting.

A lesson in troubleshooting

By Roscoe

This is a story about things not always being as they appear or how I nearly went crazy diagnosing my overheating problem

I own a Shelby Cobra replica. I built the car over a period of two and a half years, taking my time, doing it right. I built the engine up from a short block using high quality parts; AFR heads, Demon Carb, etc. The engine is a 1983 351W Ford and pushes out 365 horses; plenty of power and torque to catapult a 2400 lb car down the highway like a rocket.

Since the first day I got it on the road the engine had a tendency to run a bit hot. With a 160-degree thermostat it would run in the 180 range. However, in traffic or idling for any period of time it would creep up to over 220 degrees! I had the electric fan on constantly. I chalked this up to the quirks and nuance of a high performance engine and decided I’d have to live just with it.

About 6 weeks ago I was out one evening and noticed that my temperature gauge was pinned! Luckily I was close to home and got it into the garage with no problems. The next day I checked the coolant and topped it off. I idled the engine and it seemed fine for 25 minutes or so. Shut it off and let it cool then checked the water level and topped it off. I started the engine and ran it up to 150 degrees. Everything seemed fine and I headed out to the interstate. The engine at this time was running between 150 and 180. I ran it through the gears getting on the highway. Just after that the gauge went up as fast as a gas gauge when filling the tank. I made it home again with the radiator cap screaming like a tugboat.

The first thing I did was pull the high volume aluminum water pump and thermostat. The pump looked fine and I cycled the thermostat in boiling water six times. I re-assembled everything, with a 180 degree thermostat installed, and had the same problem.

The next day a friend came over and brought some test equipment. Suspecting a blown head gasket, we pressure tested the cooling system and did a dye test which would indicate exhaust gasses in the coolant. These tests came up negative. There was no coolant in the oil and no oil in the coolant. No white smoke coming out of the exhaust either.

Next, I suspected an air pocket. I purchased a Mit-y-Vac AirEvac system. (I believe one of the reasons we have these cars is the excuse to buy new tools!) This AirEvac creates a vacuum in the cooling system and allows you to suck coolant into the system and eliminate virtually all the air. Well I found I could not create a vacuum over 7 or 8 mercury inches instead of the required 25. What I heard at that point was a gurgling coming from my aluminum radiator. Further inspection revealed a small hole in the radiator at the bottom on the passenger side. Hmmm, could this be it? I immediately ordered a new custom aluminum radiator from Afco Racing.

Well I installed the new radiator and was very pleased with the way it went in and the new -AN plumbing. HOWEVER, it did not solve the problem. It still overheated but I noticed that the temperature did not run up while at idle but only when I revved it or took it out for a mild run. I idled the engine for about 20-25 minutes so the thermostat could open. The temperature got up to about 185. I shut it down, let it cool, and topped it off. I took it out for a spin around the neighborhood, got about a mile, and it climbed to about 210. I headed home and by the time I got back home the temperature was pushing 240!

It still seemed like a circulation problem to me so I pulled off the water pump again. I took it over to a few mechanics I know and they all said it was fine. Well I put everything back together. I made a new upper hose and routed it differently which provided a less restrictive flow. No Thermostat installed this time, 50/50 mix, new belt, air bleeder installed on the intake manifold. When I filled it with coolant the car was up on jack stands, the front up at least a foot off the ground. Checked fluid level after bringing it off the jacks and it was fine. The engine idled for about 10 minutes and with a few revs and worked itself up to about 150. The engine still seemed to rise quicker after revving the engine. I got in the car and brought the tach up to 2700-2800. Within three minutes or less the engine worked its way up to 220 and I shut it down. I opened the bleeder on the intake and no air, coolant level was fine. I also pulled the plugs and they were fine, showing no signs of steam or other symptoms.

Now for days friends have been telling me to pull the heads but I really did not want to do it. Now facing the reality I yanked the heads off. Well, I found some silicone ‘worms’ clogged in three of the crossover eyebrows in the head. One was as large as a Bass lure! It was probably silicone ‘squeeze’ from my original water pump install that broke loose. Could this be it? I was elated to find that I may have solved the problem.

Confidently, I re-assembled the engine and started it up. I could not believe that I had the same problem; idles fine but heats right up under load. I am at the point that I’m ready to pull the block and have it cleaned out but I decided to replace the water pump. Hey! It’s the only thing I’ve not replaced!

I ordered a new high volume aluminum pump. I could not believe that, after installing the new pump, the engine ran fine; better than ever! With the 160 thermostat the engine ran at 150 degrees with no fan! In traffic the engine climbed to 180 and I simply threw on the fan and it cooled down in minutes. I felt I could idle this engine all night long and it would not climb over 150 degrees! Now the question was: "What the heck is wrong with this pump?"

There was no model number on my pump, just some code numbers stamped on the shaft. I pulled my original invoice from my files and verified the model on the invoice was the correct one for my 351W. Also, whenever I received a part delivery I would double check to make sure what was on the box is what I ordered. Well I took the numbers off the water pump shaft and called the company. Guess what? I was told that this pump was for a 351C – 400! So I’ve been running a Cleveland pump in a Windsor for almost 2 years!

Some of that silicone must have clogged the system just enough to cause an overheating problem.

Lesson learned? Don’t believe what the box states. Check and double check your parts. Take it from an expert!

FFCobra Craftsman
1,004 Posts
That was some story...
Guys, I think we are dealing with a gauge problem here since the heat comes on so quick.
I have instructed Advil to check his ground since the gauge is fluctuating at startup.

I never had a heat problem with FFR1997K after proper bleeding.
The inline "T" filler that you install in the upper rad hose works the best.
The air needs to be bled out at the highest point of the coolant system.
The irregular mounting point of the radiator in these cobra's make the "T" filler a necessity.

If you are using the pusher fans as the only means of cooling the temp you are making a big mistake.
A puller fan mounted to the back side of the radiator is so much more efficient.
Those of us installing the pusher fans do so mostly for cosmetic appearance.

I have Advil checking the sender operation by placing it in hot water and checking to see if the resistance changes.
I also have him checking the ground at the sender and at the gauge.
An incorrect ground will skew the voltage readings in the comparator (Gauge).
The gauge compares the +12 volts (Reference) to the voltage of the sender.
As the resistance changes at the sender, the gauge reads the current in the circuit and displays the temp reading based on these results.
A poor ground will give incorrect reference and resistance readings.
I believe this to be the problem.

A stock 302 should never have a heat problem if you eliminate the air in the system and ensure your hoses are not kinked due to the odd routing.
A modified 302 or larger engine may require additional means of cooling, but not a stock 302....

I have a Griffin aluminum radiator and the Moroso "T" connector. I rarely need the fan to assist in cooling, even in the heat of summer here in Florida.
I am using a stock rev rotation water pump and under-drive pulleys.
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