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Discussion Starter · #1 ·
Couple things and assistance needed.

Heater core started leaking, so had a spare one, pulled the dash, got it swapped out, and evidently I pulled a wire loose and broke it internally in the harness during the job, as I have no power to the blower from the control switch. I verified the fuse (even though I don't have the diagram of the fuse block, and that the blower motor itself is good). So again, I will be pulling the whole dash and straighten that out. Need a wiring diagram so I can make sure I have things right, and to be able to identify a few other things, like power window and door lock connections so I can upgrade to them in the future.

Secondly, I have the faulty tachometer. I know the tach itself is OK because I do get a needle jump when I turn the key to on most times, but I don't know what the repair is. Heard us mention it several times over the years, so an update on that fix would be appreciated.

Lastly, and this is a strange one to me. I can drive around all day long in town and the engine does not overheat. Take it out on the highway, fine, but go into cruise mode long distances and she starts getting warmer and warmer. I have no history on the O2 sensor or injectors, but she has 186,000 miles and I don't think they have ever been changed or cleaned. Since the engine cools down from 3/4 on the gauge back to half way when I take an offramp to a gas station, I am thinking she is actually running a tad lean and the constant cruise causes the problem/issue, on and off the throttle in town or stop and go traffic, prevents it from happening. Also, at higher altitudes it doesn't seem to have the heating issue. I have never heard a problem with an O2 sensor causing a lean condition, it is always a rich condition. Is there any other sensor that could be causing this issue? Possibly MAP sensor? Not overheating at idle and things is what has me puzzled, as all other possibilities have been done (water pump, clutch fan, hoses, gaps around radiator, air pocket, etc.).
 

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I would take a look at the blower motor resistor before you tear anything out. It's pretty easy to access on that model.
 

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1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
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See p. 8W-42-7 and 8W-42-8 for the blower switch & resistor diagrams.
 

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So, the tach doesn't read anything? Could be a bad solder joint on the tach drive board, or it could be the board has a loose connection to the main instrument panel board. It uses an edge card connector. BTW, that board by design, not by failure, pulls 100mA with engine off. It's because it receives both battery and ignition power, and the battery power partially turns on a transistor, which allows current to bleed through a Zener diode to ground. The fix is to cut and jump the battery trace to the ignition trace, so that it draws no current when off.

The overheating suggests poor cooling at speed, and I would check the radiator fins to see if they are intact. I would also suspect the cooling system might be partially clogged, especially if the heater core recently failed. Finally, check for dragging at speed, such as calipers or driveline.
 

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Discussion Starter · #5 ·
Thanks for the replies and wiring diagram and the tach fix.

Pretty sure it isn't the radiator or flow given it cools down as quickly as it does, an off ramp coast brings it down to almost normal temp, a coast of only a couple hundred yards, so don't think it is flow restriction. It takes about half an hour the first time she warms up above normal, usually about 15 minutes or so once I stop for gas and start again. Outside temp doesn't matter, but if at a higher altitude, it does not do the extra warm temp, say, above 3000ft or higher, then again when I drop back down to near sea level. I thought it was a hose, which did an internal split that slowed coolant flow down, but that got fixed and it was another year before I went on a long trip and noticed the same circumstances. I can also, while doing the long trips at cruise, to back off the gas about 6-8 seconds at a time, about once a minute, and the temp does stay down, but that is horrible driving and it only slows the problem, not completely fix it.
 

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Discussion Starter · #6 ·
I would take a look at the blower motor resistor before you tear anything out. It's pretty easy to access on that model.
The motor works, I tested it before installing, just no electricity to the switch when turned on.

The heater core got a leak on the top nipple inside the engine compartment. The truck itself (heater core) has roughly 350K miles on it, and it was a small leak, figured I would replace the whole HVAC unit since I had one from my other '95 with 145K miles on it and in parts storage (ten years of storage). I think I simply pulled the wiring harness a little too tight when moving the dashboard to get the whole unit out, but wanted the wiring diagram for other plugs not being utilized (the original truck had every single option prior to being totaled by a "friend"), and contemplating installing the power windows, door locks, tilt steering, cruise control, among other things, and wiring will be needed to verify those things, and since I didn't have the diagram of what the fuse box fuses was, checking every fuse was time consuming, but now I know where to look.

So thanks to all, will be taking care of these things over the next week or so, no rush, it's 65-75 degrees and no need for the defroster or heat right now. At least she doesn't leak again.
 
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2017 Charger Pursuit AWD
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You may have just gotten a parts-store-junk fan clutch or thermostat.

Assuming you have the 318 Magnum,
Thermostat is - 52028185AC, list is $17.45
Fan Clutch is - 68064766AA, list is $184.00

Other thoughts -
A rich mix of antifreeze, like 70/30, could result in higher temps, maybe water it down to 50/50, see what happens.
A plugged/partially plugged cat can raise heck with temps.
Setting aside the possible 02 sensor issue, give it a big drink of one step up in octane, see what that does. If it helps at all, run 2 of the big bottles of Techron FI cleaner through her (dump em both right in). Take it out on the highway and give it a good old fashioned 'Mopar Action' tune-up (plenty of WOT, to blow the snot of of it). If ya blow it up, give it the 360 she really needs.
 

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Discussion Starter · #8 ·
The antifreeze mixture is 50/50 right out of the bottle, and when the lower hose got changed just in case it was collapsing, fluid was nice and clean. When the water pump itself was changed, when the radiator was drained and pulled, I backflushed it to make sure it was flowing good and nothing in it, it was a new radiator two years earlier and is the largest one available for the Dakota, so an upgrade of that isn't it. The ability to cool down as quickly as she does, and the fact the heater does not totally burn me out of the cab when she is warm just leads me to believe she is running lean and cruise driving increases the temp.

, She is a 3.9, and internally she is clean, no carbon build-up, cat was replaced with a new one and only has 20-25K miles on it, it passes California smog check every two years without an issue, so if the EGR was bad I am sure I would hear about that and fail smog test.

I guess fuel injector cleaner would be the next most logical step before replacing the O2 or injectors themselves.
 

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I'm still thinking that one possibility is that there is excess drag somewhere that makes the engine work harder at higher speed and overheat. Calipers are always cool? Power level is good at speed?
 

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Discussion Starter · #10 ·
Nope, she coasts just fine and the brakes are not dragging. The real weird thing was about a month ago I was heading out to AZ to paint the daughter's house and since the fuel gauge started losing its rheostat, the gas tank light comes on when I have half a tank of gas, so I was watching that. Needless to say, I ran out of gas, guess I missed the low gas light what with the sun shining on the dashboard. Anyway, as the temp had been climbing as usual, when I ran out of gas and was coasting before pushing the clutch in, I literally watched the water temp needle start to drop down to normal temp straight up and down, about a 15 second period. I know it is actually getting warm because many years ago when the temp went up and was just about pegged, she started to ping from overheating, so I have been extra careful since then. It doesn't prove there isn't anything blocking the flow, but not cylinder firing shows the flow is not the issue. At high altitude it doesn't overheat, only at low altitude cruising. Being on and off the gas keeps her from overheating, it is only constant cruise and takes about 15plus minutes of doing so.

Any possibility of the MAP sensor not reading altitude properly, where being on and off the gas allows the O2 sensor to overcome the slight lean condition? I know when you run rich at high altitude you shut the engine off and allow the computer to recalibrate. And like I said, if there was a problem that is identifiable, CA smog check is sure to let me know. Heck, they found one number of five on the catalytic converter that was wrong and I had to get the proper one.
 
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