How does cooling work?

Hi! 96 Cobra, running up to 210F hwy speeds and going around town. Fan kicks on at 208f and temps drop but not far enough to turn fan off at 198F shut off point. Fan is on even during hwy speeds and not sure if it's supposed to kick off.

I've got a 185F thermostat, mishimoto radiator, and a Lincoln Mark VIII cooling fan hooked up to the ECU fan wires. Replaced cooling fans too. Did burping procedure even.

My questions are:
1. Is my fan supposed to turn off during highway speeds?

2. If my thermostat is 185F, shouldn't my temps be around that or lower than 210?

3. Do all Cobras that are stock besides cooling upgrades run like this normally? Get up to 208, fans kick on, temps drop down to around 200 until fan kicks off (or sometimes doesn't) then raise back to 208-210 and repeats regardless if I'm idle / low loads.

I do not have the lower air dam, side air dams before the radiator, I have no condenser, and no radiator cover that sits on top of core support. Getting them added soon to test.

I'm not sure if the temps I'm seeing are normal or if I should be lower than the low fan kick on temps (208F) even running at idle / low load. When my fan kicks on, it's at full speed which worries me that it isn't enough to cool it down enough.

I'm just curious the technical aspects of the cooling system in the Cobra.

Thanks in advance!

Keep replacing the missing shrouds/air dam. They are there for a reason. What is the outside temperature while you are making these observations?

Tillerman77 said:

Keep replacing the missing shrouds/air dam. They are there for a reason. What is the outside temperature while you are making these observations?

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During winter and around 30-40 out and even now when it's been up in the 70s. About the same results.

The thermostat I'm worried might have a smaller open diagram / flow rate than an OEM.

Engnen is designed for the 200 range , up to 230 is close to the edge . Can you program the fan to come on sooner ?

ashleyroachclip said:

Engnen is designed for the 200 range , up to 230 is close to the edge . Can you program the fan to come on sooner ?

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No tuner at the moment. I know 240 is the absolute top limit I'd ever want to see, and 250 being dangerous / warped heads area, so I like to keep 230 as the absolute max I should ever see but the fan is on almost 24/7 at low speed, but the fan is technically high speed / maximum output since it's single speed and it's worrying that it doesn't cool down as well as I'd expect.

How old is radiator?

I had this battle on my 03

took a lot of leaning and testing but got it

Serfma said:

Is my fan supposed to turn off during highway speeds?

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Unless it is insanely hot outside, yes.

Tillerman77 said:

Unless it is insanely hot outside, yes.

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Ok currently my fan does not turn off regardless of speed. Using OBD2 to read fan on / off and it stays on.

hotcobra03 said:

How old is radiator?

I had this battle on my 03

took a lot of leaning and testing but got it

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Not very old, month or two. Old radiator vs new did not change any cooling characteristics. Only replaced rad because it (was aftermarket too) started leaking

Serfma said:

Ok currently my fan does not turn off regardless of speed. Using OBD2 to read fan on / off and it stays on.



Not very old, month or two. Old radiator vs new did not change any cooling characteristics. Only replaced rad because it (was aftermarket too) started leaking

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have you done a compression test?

Did your 96 have the cooling recall done?

98 svt said:

Did your 96 have the cooling recall done?

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Negative. I upgraded radiator, fan, hoses, did 185F thermostat. Few owners through this car lol

Also compression check not yet, list of things to do. I did a head gasket replacement months back because I was running hot and I had one bank about 40psi higher. Haven't checked compression since.

Refresh my memory, the car does not overheat sitting still , but does on the hiway at 60 - 70 mph ?

ashleyroachclip said:

Refresh my memory, the car does not overheat sitting still , but does on the hiway at 60 - 70 mph ?

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Basically it will get up to 208F, 210F tops, fan kicks on then will drop down to maybe 198F sometimes where fan kicks off then repeats. Last night after a good drive around town I came to an idle at 205F for a solid 5-10 mins with fan on.

Hwy speeds fan stays on, does about the same thing as above but never drops below 198 while driving. Maybe reached a tops of 215F if I'm uphill and if I leave it in 5th (normally forgetting to downshift into 4th)

Serfma said:

Negative. I upgraded radiator, fan, hoses, did 185F thermostat. Few owners through this car lol

Also compression check not yet, list of things to do. I did a head gasket replacement months back because I was running hot and I had one bank about 40psi higher. Haven't checked compression since.

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you need to check the AC condenser which was also part of the recall/upgrade. They went from 22 to 16 fins per inch. Old on the left, updated on the right



I know not exactly the same but my Mach has the big ass procharger interoocler in front and with a 180 stat if Im running down the highway I never even see 200, if its cooler out (say 60 or less) it'll run right around the thermostat temp.

DSG2003Mach1 said:

you need to check the AC condenser which was also part of the recall/upgrade. They went from 22 to 16 fins per inch. Old on the left, updated on the right

View attachment 1697305

I know not exactly the same but my Mach has the big ass procharger interoocler in front and with a 180 stat if Im running down the highway I never even see 200, if its cooler out (say 60 or less) it'll run right around the thermostat temp.

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Forgot to add I don't have an a/c condenser! Haven't had one since I got the car.

I'm betting on the stock camshaft sprocket timing being off, since I've read the 4v suffers the most since the sprocket keyways have a lot of free play. Didn't know about it until after I put it all back together. Lol.

Also thinking of borrowing a vacuum tool to pull vacuum on the cooling system and fill it up that way to ensure no air bubbles.

The lack of the lower air dam and associated side shrouds is causing issues for cooling. The lower air dam forces cool air upwards towards the front of the core support, while the top rad cover and side shrouds directed air towards the A/C condenser (IF it were still in place) and through to the radiator. Without the lower dam, top cover and side shrouds, the air isn’t passing directly over the radiator as designed.

Some will argue against the above saying it doesn’t matter since you have removed the A/C condenser and the fact that you’re running a different radiator. The problem is, the lower dam, top cover and shrouds served a purpose to direct the air into the core support, over the radiator. Without them, the air is not being streamlined directly over the radiator when in motion.

Factory fan turn on was in the 208*-210* range, so if you’re data logging those temp ranges and seeing the fan kick on, you’re within spec.

At highway speed, the fan shouldn’t even be on - UNLESS you have the Defroster on OR A/C on. If the HVAC knob for Defroster or A/C is selected, the fan would turn on - it’s by design. The fan would click on and off to cool the radiator but also to keep air moving over the condenser, since you don’t have a A/C condenser anymore, that aspect doesn’t matter... BUT if you’re still using the factory fan with CCRM hooked up, and you use Defrost OR A/C mode, the fan will still click on at speed or idle.


1994+ Mustangs have the CCRM (constant control relay module), which is the larger black module with the large connector going into it. This housed the relays for the fuel pump as well as the relays for the factory fan. If the car still has the CCRM and you’re having issues with the fan, it could be a failing or failed relay within the CCRM. This module was like a 5”x3” black metal box, with a very large connector and was normally located on the passenger side, near the back side of the core support.

Also, check the connector from the engine harness to the factory fan. IIRC, there was a Ford TSB a ways back for the electrical connector that plugged into the fan. That connector would melt or burn up, causing damage to the fan connectors. You’d have to pull the connector off the fan to check for bridging or melting of the connector on the harness OR at the actual input for the connector on the fan. Any damages, replace the fan OR the connector on the harness.

Another misconception with the thermostat on the OBD Mustangs is the “turn on” and “turn off” for the fan is programmed into the PCM logic, it’s not working by thermostat temps. You can put a lower thermostat in, but it’s not going to matter because the fan is still going to kick on/off based on the PCM logic.

If you want the fan to be “controlled” more, you either have to get a tuner device to change it, a pre-canned tune from a Pro Tuner Shop or have someone that can modify the PCM factory fan turn on/off parameters.

The only other way around the factory fan on/off logic is to completely bypass out the PCM and CCRM and install an electric fan thermostatic switch that the user can program (dial in) their own on/off setting for the fan.

On my 94 Cobra, I’m running dual 10” SPAL puller fans with a Hayden dual fan controller. My PCM and CCRM is completely bypassed for the fans. The fans are wired directly to the Hayden controller and dialed in for a predetermined on/off based on my factory 190* thermostat.

Be careful running “cooler” thermostats other than factory as well. If the thermostat is too cool it can actually cause more detrimental issues to the engine especially during long term use. There’s plenty of docs and facts online about this, so I’m not going to get into it here - easily googable... The skinny is, factory thermostats at factory recommended temps are perfect and operate better as designed, than the ages old myths that putting in a “colder” thermostat is better. Back in the initial stages of the original Mustang 5.0 movement of the 80’s-90’s, many were using 160* stats, it as the rage back then, but come to find out years later - it’s not the best mod to do and doesn’t serve any gains on any street car, especially N/A.

Make sure your electric fan is also spinning in correct direction, it should be pulling air through the radiator, not pushing it. To test, put tissue on front of radiator or grill, get fan to kick on and it should suck the tissue into front of grille or radiator.

The 1996+ Cobras are a bitch to “burp” air from after any cooling system repairs or upgrades, due to the cross over tube design... I know as I also owned a prior 1996 Cobra.

I always used this advice here when burping 1996+ Cobras and it’s always worked flawlessly (note image shows a 03/04 Cobra engine but it works for any prior Cobra back to 1996):
Ford 4.6L DOHC Coolant Refill & Burp Procedure by Reische Performance Products

I hope something above helps.

210* running down the road is perfectly within reason .
My totally stock triton V10 runs 198 to 210 all the time , winter or summer .