Running Hot

I thought I might as well start a separate thread for this issue I’m having and see what ideas are out there! I know these issues have been talked about before, but figured I’d see what people thing of my situation.

My Cougar has been running hot, according to the TEMP gauge in the dash. Of course it doesn’t give me an actual number, it’s just a needle on a scale. But it’ll get up there about 3/4 of the way up, sometimes more.

I have a 289-2V with A/C, and my factory 24" FoMoCo radiator and 7 blade clutch fan. I think it’s actually a 3-core radiator since there’s no empty space like you’d see with a 2-core. Anyway it must have been re-cored at some point because it’s in good shape. 180 degree thermostat was installed at the time of the engine rebuild. It seems to work since the top hose gets very hot.

Chasing this issue, I took the radiator in to a radiator shop recently to see if it needed to be boiled out, if there was scale buildup. I also had one little leak at the top tank. The guy there (old cranky 74 year old who has been doing this forever) gave it a flush in both directions and there was just a little bit of dirty water that came out. He said it didn’t need to be boiled and didn’t want to waste my money. He patched the leak, and I touched up the paint and put it back in the car. The issue persists.

Another thing I’m about to try is a different fan clutch. The one that WCCC has been selling (which I have on the car now) isn’t the one that Hayden calls out for this application. Looking at it, it seems like the fan isn’t far enough into the shroud. So I ordered one , and as soon as that arrives I’ll be trying that, but I’m not sure if that’s going to entirely solve the issue. Here’s a view of where it’s at now:

I recently had a tune-up done and the timing is now set to 6° initial (factory spec) and 30-something total advance. It was also running hot when the timing was further advanced.

Running 50/50 distilled water and glycol with Water Wetter added. When I put the radiator back in, it drank a gallon of each plus a little extra. I thought the capacity was more than that, but I guess there was still coolant in the block. Anyway, still hot on the gauge.

I need to take an infrared thermometer reading and get back to you on what it says. What should I be looking for? Is the upper hose the ideal place to measure temp?

Is the default happy operating temperature supposed to be in the middle of the gauge like I’m used to seeing on other cars?

Does paint on the radiator fins make any difference? There’s also the A/C condenser in front of the rad, and I painted it black as well. Wondering if that contributes enough to partially block airflow.

Also wondering if I should ditch the fan clutch entirely, use a spacer and run it directly. Not sure.

Open to your ideas!

The repro sending temp units have the incorrect resistance. They make the gage read too high. Get an original one and it normally fixes the problem.

If the radiator is 50 years old it might be that the tubes are all coated with corrosion on the inside. If so there is only one solution. New radiator.

The fan looks about right, should be 1/2 way into the shroud.

A few years back someone documented aftermarket vs FoMoCo temp sending units. The first value is aftermarket, while the second is the NOS temp sender he measured.

Obviously you’ll need an infrared to compare to, but in the meantime it’d be interesting to see where your high and low values lie.

It should read about 195 -/+ degrees at mid gage.

Wow - off by more than 50% at 212 where you need to know! That says a lot.

All I can add is when I was chasing some heat issues in my rebuilt 390 the biggest difference I got was when I replaced the run-of-the-mill re-popped fan clutch with a higher end (re more expensive) fan clutch that the Shelby guys recommended.

  • Phillip

All very interesting ideas! I’ll see if I can get an original temp sender. I drove the car at lunch just now and after getting back I kept it running and got out the cheapo laser temperature reader. Was getting readings that seem fairly normal, ranging from around 180-200 on things like the upper rad hose, top tank, and the temp sender itself.

Do you remember what it was? I know Hayden makes various grades of clutches, but they don’t have a heavy duty one listed for my application. Just the basic one.

I had the same issue with an aftermarket temp sending unit. After installing it I was reading up near the hotline. I took it out and put an original back in and was back to the mid range.

Phillip, I too would like to know which clutch you used because I have not found one that did the job.
Instead of locking up when hot, they got much looser.

From what I’ve gathered, they never really lock up all the way. But you’d think it would get tighter! On Hayden’s website they describe the different levels of clutches they have:

Standard Duty
Turns fan 60-70% of shaft speed when engaged
Disengage to 20-30% of the shaft speed
Used with lighter pitch fans (1-1/2” of pitch)
Flat plate impeller design with up to 11.4 sq. in. of working surface
Identified by a smooth steel faceplate & thermal spring assembly on the front side

Heavy Duty
Turns the fan 70-90% of the shaft speed when engaged for increased cooling
Turns the fan 25-35% of the shaft speed when disengaged
Used with deeper pitch fans (2-1/2” of pitch)
Land and groove design with up to 27 sq. in. of working surface
Identified by finned aluminum faceplate and thermal spring on the front

Severe Duty
Turns the fan 80-90% of the shaft speed when engaged
Turns the fan 20-30% of the shaft speed when disengaged
Used with deeper pitch fans (2-1/2” of pitch)
Land and groove design with up to 72 sq. in. of working area
Larger working surface provides cooler running and longer life expectancy
Thicker body and deep finned faceplate dissipates more heat
Can be used in place of many heavy-duty clutches

Their part # 2710 is the only thermal clutch they offer for a '68 Cougar and it’s Standard Duty. Since it only gets about 70% of the shaft speed, this is why I was thinking of converting it to a fixed mount. But I will try the 2710. Right now I have a 2711 on it for some reason. Did WCCC’s former purchasing agent make a typo? Hmmm

I got it from Chris Brown -

I heard someone say at a car show that maybe it is a Jaguar part?

  • Phillip

I’m hoping this sender will give me a more accurate read on my 390. I’ll let you know if it works.

Those measurements are not for the vintage sending units we all know and love, but are from the mid-70’s on up. Our sending units run from 13 to 73 ohms, full scale.

Do not believe these numbers, they are not correct at all, not even close!

The plot thickens. I found an original Autolite sending unit but it didn’t seem to work. I got no reading on the gauge. Then when I went to pull the wire / elbow connector back off, it broke. So now I get to splice on another elbow plug.

Any experience with the Motorcraft unit that’s still available new? Surely it must be more accurate than the generic repro?

Anyway I think changing the fan clutch helped, but don’t have data yet to confirm.

To understand a heating issue you have to be specific about when it over heats. On the highway, the fan and fan clutch are irrelevant. The ram air effect is putting more air through the radiator than any fan you can fit. If it over heats on the highway, you know that you are getting enough air. In that case you focus on heat transfer. The heat is carried out of the engine by the coolant. Coolant flow is most often limited by the thermostat opening size, or obstructions in the radiator. Keep in mind that power equals heat, so on the highway your are making more power and more heat. The highway is the big test. If it gets hot at traffic lights or putting around town and then cools down on the highway you are not getting enough air. This is where you look at the fan shroud fan clutch, most commonly the fan clutch isn’t locking up.

Good thoughts Bill. I was wondering about the thermostat. I looked back at receipts and I just used a standard 180 degree one. And I assume I put it in the correct way…
Radiator wasn’t plugged so I don’t think that’s it, but I wonder about the block. I’m not sure if the machine shop did anything to flush out water passages when it was getting rebuilt.
Anyway, my suspicion now is that it’s actually okay. I just need to find a sending unit that will give me an accurate reading. I just tried a used Motorcraft one I found here at the shop and it read pretty far down on the Cold side even when at full operating temp. Argh.

I don’t know how much difference there are in calibrations, but according to my MPC the sender you posted at Summit is not correct for your car. I show the following from my MPC (April 1973). This also might help in your search of the used ones at WCCC.

67 to 69 all except (69 351) use a C6DZ 10884-B (SW-552)
69 351 use a C9WY 10884-A (SW-888)
70 302 HO & 428 & 71 429 use the one that you posted D0ZZ10884-A (SW -925)
70 351 use a D0WY 10884-A (SW-924)

I don’t have obsolete superseeded books to determine if SW-552 was updated at some point.

Did you put a new water pump on the engine when you rebuilt it or just use the same one? The impeller fins corrode and disappear over time.

My cooling system was in really bad shape when I got my car, so after multiple flushes, I ran a garden hose through it for several minutes before the water stopped coming out rusty and came out clean. If you’re shedding rust into the water, it’s going to thicken up and not transfer heat so well. Might try flushing with Thermocure Evap-o-rust.

I have a temp sender from your shop, and it reads about 1/4 from the left when I’m at 180 – doesn’t even get to the T in TEMP.

For the technically minded. Buy a good quality 5 watt 100 ohm linear potentiometer. (variable resistor). Use a good aligator clip lead to ground one side to the block and then another clip lead to the end of the gauge wire. Adjust the potentiometer until the gauge is reading mid scale. Be patient, as the instrument voltage regulator is pulsing at around 5 volts and the gauge needs time to settle. Once you see the reading you want, disconnect the pot and read the resistance. This now shows the value you want to see from the sender. You may wnat to take readings for several places across the scale.

Next, see what the sender is really doing. Put clip leads attached to your meter on each end of the sender, and then drop the sender in a pan full of water on the kitchen stove. Use a candy thermometer to read water temp. Take note of the resistance at different temps up to boiling at 212 degrees.

Now combine the data to understand what is really happening.

Thanks for the info. You may be right, I tested another used one today that was marked Motorcraft and had some remnants of red sealant on the threads. After driving the car and getting it up to full operating temp, the gauge was still just barely above the “C”. So that’s a no-go.

Yup it’s a new water pump. And that’s interesting, sounds like you have the opposite problem with the aftermarket sender.