1983 Mustang 3.8L overheating

[04BlueGT]

Okay, so it's overheating badly at idle. Seems fine on the road.

What's been done:

Engine rebuilt. Block and heads tanked and professionally checked. Heads had some minor work on them to clean them up. New gaskets everywhere and no passages were covered by gaskets. Removed all the EGR garbage and smog pump. Trans is rebuilt and recently checked out as good to go.

Crank is reman. Rods are original, everything else is new.

New: 2 core aluminum radiator, 2 x 12" fans, new water pump, new temp and fan sensor, new hoses, new heater core, separate trans cooler, checked wiring, etc. Fans work and are pulling air the correct direction. Timing is correct. Belt is new, properly tensioned and routed. Gauge is fine.

With the cap off the radiator and the car running, I verified good flow of coolant and the thermostat is working (180*) as it should.

Folks, I'm flat stumped at this point. I water flows, stat opens, fans run, still too hot. I need help to get my daughter's car to run right. Anyone have any clue as to what next to check?

[Walking-Tall]

I had an '83 and now have an '86, both with 3.8L V6's, and never ran into this issue.
Before reading your post, I assumed you'd say you went out the highway and POOF, and then continual overheating after that, which I did run into with my '83, which was a blown head gasket... common with these. Pressure testing the cooling system is a good verification that everything's okay inside.

I'll ask my dumb question first...
The water pump is rotating counter-clockwise, with the back of the belt running it's pulley, right?
Clear verification of flow with the cap off the radiator will show the driver's side rad tank's coolant getting drawn down when the thermostat opens, and coolant flow out of the rad's internal tubes, passenger side to driver side. Is that what you got?

Overheating how badly? Blowing out into the overflow tank, out of the rad cap, or just by the gauge?...

Factory temperature gauge? You might try the old or another temperature sending unit.

Actual numbered/mechanical gauge to see your temperatures?

"Seems fine on the road" (natural sufficient cooling airflow) sounds like fans not doing their
job while the car's stationary... odd...

[plstktnkr2]

If it is overheating and blowing into over flow , check your rad. cap. Also what degree thermostat did you put in ? check with a known good gauge

[04BlueGT]

I appreciate the feedback thus far. I purchased an IR thermometer today to check temps. Water pump is new, belt is correct, and water is flowing. I verified by looking with the rad cap off. Also verified thermostat is functioning. It's not pushing water out the cap, but replaced the t-stat and cap recently anyway. Stat is 180* as required. I replaced both the temp sensor and the sending unit that controls the fan. Both were new. I upped the fans from the one stock to two 12" fans. Both are pulling as they should and air flow is substantial. Still, the stock gauge is off the scale. The temp of the goose neck was about 220*

Maybe this helps, maybe not. I used the IR gun to measure cylinder temps at where the manifolds attach to the heads. All cylinders were fairly close at 492-508*. 16* is nothing to worry about. But I don't know if that's abnormally high or not.

Oil is good - no signs of a head gasket issue. I'll do a compression test to make sure in the very near future, but I'm not sure that's it.

I'm starting to think it's an electrical/gauge issue. The wiring on this thing is 32 years old and I've already replaced some of it.

[JTurbo]

Did you try a mechanical temp gauge? I'm wondering if the coolant sender is fubar....

[04BlueGT]

Sender and sensor are both new. Twice. IR temp gun put goose neck at about 220 degress. I think fans come on at 225. Honestly, I'm leaning towards wiring or gauge now.

Thoughts?

[plstktnkr2]

Have you tried a different gauge? your gauge may be the issue...

[Walking-Tall]

I'm not familiar with temp-sensor-controlled electric fans, but if they're not coming on until 225-degrees (seems awfully high to me), I'd say that might be your answer/reason the coolant is hovering around 220-degrees, until, as you said, you're out on the road... I know that in theory the thermostat's rating is a minimum, but with your equipment, and really anything that where everything's in good working order, the coolant should run the number of the thermostat you've got in it, no matter if idling or going down the road.

Is the fans' temperature-on setting adjustable? If so, I'd want to see them coming on at least at the thermostat's rating, in order to do their job (reduce temperature to below 180-degrees) because 225-degrees seems way too late coming on to maintain anything near 180-degrees, and also seems like a real good reason you're measuring 220 at the thermostat housing.

Leaning me again to mention the fans not doing their job, while the car's sitting idling. Maybe they're hauling ass after 225-degrees, but by then, since once the thermostat is open it's all up to the fans or going down the road for it to be able to cool coolant enough to close it again, fans not coming on until after 225 isn't doing anything to coincide with less than 180-degrees. The only way the thermostat can close again is if the rad and fans and water pump put less than 180-degree coolant back into the engine.

I agree with you about the wiring in these. I have fixed enough bad past "fixes" and covered up a fair amount of dried and broken away wire insulation on mine too.

Along potential electrical reasons, have you checked the voltage at the battery at idle?
Maybe low charging could affect idle sensor/sending unit function...?

Good luck with it, it is a strange problem indeed.

[04BlueGT]

Not playing with her due to schedule, but I'm going the electrical route or gauge. When I can get to it, I'm pulling the cluster and verifying all the connections are clean, intact, and fully seated.

[mustangxtreme]

The electric fans on these are more than capable of cooling the engine down but draw a lot of current. The fan relays leave a lot to be desired. The contacts in the plug push onto a circuit board and they will end up with poor contact which will melt the connector making things even worse. If I had to do it over again, I'd replace the factory relay and plug with an aftermarket one. I would bet a failed relay/plug cause most 3.8L head gaskets to fail prematurely.

[04BlueGT]

Pulled the cluster and checked the connections. It all looks fine. Wiring seems in order, also. So, I'm down to a gauge. NPD has them for $42. Damn, I hope that fixes the issue.

[Walking-Tall]

How did you make out?

[Haystack]

220° sounds way, way too high for the fan. I bought a cheapie controller for mine and adjusted it to turn on the low speed at 190°f, as that's what the thermostat was rated for. I figured that the mechanical fan ran as long as the engine did, so why would the electric one be different. It cooled well enough I didn't even run the high speed (Taurus dual speed fan) and if never really got hot even in 100°f summer stop and go traffic.

Most newer cars that control the fan with the ecm turn the electric fan off at speeds over 40mph. My mechanical fan came apart and took out my fan shroud but spared the radiator. I pulled the fan off expecting to spend the next few hours limping it home, but as long as I kept the car moving it didn't overheat, even with no fan at all.

I always figured the thermostat rating was the fully open position... If you throw a 190° stat in water and bring it up from cold to a boil, it stops contracting before the water is fully boiling, or at least mine did.

[04BlueGT]

Okay, we can finally close this post. I purchased a Ford NOS gauge from NPD and installed it. Unfortunately, that did NOT fix the issue. After stepping back and really thinking about the problem, it hit me. Single wire sensor are absolutely dependent upon the motor to chassis ground to work right. I checked the ground strap on the back of the passenger head and, sure enough, it was loose. I tightened the bolt and the gauge works just fine.

2 notes of interest: 1) NPD (Nat'l Parts Depot) sells replacement circuit assemblies for the gauges in old foxes. Since this one is 32 years old and showing it's age, I'm replacing it and the regulator. 2) I have a NOS Ford temp gauge for sale, lol.

Thanks for all the advice. With that sorted out, I can move forward and I should have the interior finished by February at the latest.

[Walking-Tall]

Glad you got it figured out!