Checklist to make sure the car runs as cool as possible

95 4.0 lump: Needle goes up to just above N when idling or in slow traffic, never into H zone. If I am going to run the traps to make sure I don’t overheat when I move to AZ, what do I do?

I’m thinking stuff like:
what’s the best coolant, (after a good flush) and what % water to coolant
is the aux fan a weak design and should be upgraded
should I try to turn on the aux fan at a lower temps though the sensor or install a manual override
I have a 185-deg thermostat in the car already
are there any modification to make the car run cooler

Hi Wes, I have a 94 4.0. I recently did a cooling overhaul which included all new hoses. (The basta&d hose included) New thermostat and aluminum radiator. Cleaned out the overboard tank which was full of gooey ooze. I have a fair documentation posted here which you can search for.

Since doing the overhaul, my needle goes 1 needle over N but never higher. I’ve driven it for maybe 3-4 hours at 85 mph in summer here on the east coast (NC, VA and MD)


I can drive at freeway speeds in 85+ heat - no issues. Its in traffic and at stoplights that concern me

Regarding the % ratio do not go above 50% inhibitor as the effectiveness is reduced.
If the car has flaps on the radiator shroud make sure they are pliable and seal when the car is stationery if it has the twin fans then just make sure they are both working when the engine requires them to.

there’s some good points!

I don’t think the 4.0 suffers from the heat issues as do the V12’s. I’ve driven mine through D.C. traffic, local not interstate and needle was solid.

If a 4.0 can stay at N going past the White House/Capitol during rush hour, it can go anywhere.

Good call on the flaps. The cardboard gets hard over time. I replaced mine with neoprene and checked to make sure the single fan actually worked which it did with a new relay.


“If a 4.0 can stay at N going past the White House/Capitol during rush hour, it can go anywhere.” been there and done that: a challenge for any car in one of thoes 100-deg 100% humidity days. Checking those flaps Monday, and rigging a little bypass to check the fan.

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Look up my coolant system refresh thread. Look very closely at the condition of the radiator. I had many fins missing.


Radiator inspection: fins look good, just a few bugs. Aux fan is a pathetic and puny looking thing. Flaps seem, if anything, a bit stiff. Struggling to understand their purpose, too.

The radiator shroud flaps aid cooling. When the car is stationary the flexible flaps should close allowing the fan to pull more air dierctly through the radiator. When the car is in forward motion, the relative wind pushes the flaps open to allow additional cooling air, above what the fan can pull, through the radiator around the fan. If your flaps are hardened and/or bent partially open they will reduce cooling efficiency while your car is stationary and when moving forward.


Help me understand: so when the car is not in motion, the flaps should close. Got that. But if the car is not in motion AND the aux fan is working, I would think the flaps would be open. They are right behind the aux fan location. I’m bypassing the relay shortly to observe what happens to the flaps in that situation.
My issue is when the car is not in motion, or slow in traffic, and its warm outside. In this case, the aux fan should be running and flap open to allow the air from the aux fan to go through the radiator. But… to your point, if the flaps do not open when the aux fan is on, the aux fan is quite limited in cooling capability, no?

well, first test failed. I confirmed I had 12V to the power pin of the relay, jumped pins 30 to 87 and nothing. Double checked the wiring diagram from the 95 electrics supplement to see if this was a direct power (battery to fan with nothing else in series) it is, so the fan should have come to life. Something in the aux fan power is broken. This looks like a ‘bonnet off’ job, so it will need to wait. I’m in the process of a move, so proper tools are packed.

Gordon, Aircraft Spruce has 3" wide material, requirement is for 3-3/8" for flaps so I went to ebay. Found 1/16" x 12" x 24" for $15.15 all in.
Once the bonnet can come off, I will verify the fan operation wiring, and at the fan and probably replace with a nice Fluidyne model

Wes, I don’t think the bonnet needs to come off. I replaced several rubber bushings that had perished on the fan. I was able to complete the task by removing the grill and a couple black plastic finishers. Removing the bonnet seems a bit extreme unless you have hands the size of baseball gloves!

Not sure if the 95 has it but there is a switch installed in the top driver’s side of radiator. A temp switch which on my 94 was inop. My fan barely turns on, frankly I’ve only heard it run twice in a couple years.


When the car is in motion the flaps will open to provide additional cooling.
The reason of these flaps is that when the car is not in motion, and there is no air pressure at the front of the radiatior, hot air from the engine compartment does not escape from the openings and get sucked back in by the fans, thus compromising the cooling.

I’ll give it a look to see about removing the grill.
My test bypassed the temp switch, sending power directly to the fan (which did not respond)
If that grill access gets me anywhere, I will be able to test the fan further with a long jumper. BTW The OEM fan motor seems to run about $350 to replace. Yikes. Nice aftermarket fans are less than $200.
I’m hoping its a simple wiring issue.


How your oem fan looks like? Is it mounted in a same way as on V12? I might have a solution :wink:

I will check that and let you know

Not mounted like that. My car has a shroud around the fan.
The shroud and fan does not clear to be removed, either. (that I can see)
I was able to test the fan itself today and the problem is certainly with the motor. I could not turn the blade: froze up solid. Checking manual for removal process, but I have a bad feeling about what needs to be removed in order to remove the fan.