Problem: The temp needle goes all the way to the end of the normal operating range on the meter then it will drop down about a quarter of an inch for a little while then it will head up to the end of the range again then back down again in a somewhat cyclical fashion. It never goes to the extreme point of the meter but it does not stay in the middle of the gauge when at operating temperature. I have replaced the thermostat with a new one a few days ago, no change. I have not checked the timing or dwell, it was supposed to have been set by the guys I got the car from, "service technicians" from the local high end car store.

I sealed the exhaust stud threads and as far as I can tell I don't see anymore coolant leakage or steam from there nor does there seem to be any exhaust fumes coming from the radiator.

I removed the passenger side 3/8" drain plug and the coolant flowed from there fast and free, no rust. I didn't see any blockage or any indication of slow flow.

I removed the front and rear driver side freeze plugs and while there is some rust and chunks visible I did not notice any visible blockage there. I will replace the freeze plugs as indicated with the blue sealant tomorrow, but I wonder as to the next step.

I checked the radiator with my hand and it is hot on top and cooler at the bottom, like it seems it should be.

Question is, I can get the radiator boiled and cleaned for $65 but given the age do I just replace it with an aluminum rad from ebay? But before replacing, should I use a de-scaler/de-ruster in the engine before-hand?
What about vinegar then baking soda?

I figure I will go ahead and get a set of after market oil pressure/ammeter/coolant temp gauge set to see if there is something amiss in the gauges.

What do yall think?

Thanks in advance.
John

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Psychics will soon lead dogs to your body!

1963 Dodge Dart 270 convertible

I just thought I'd throw out there while you're searching for the answer to this problem, that in a pinch, the bright green bottle of "wetter than water" coolant additive really does help bring it down. But like most other things, it's best to just solve the problem.

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1965 Dodge Dart
'85 225 /6
Holley 1920

"just give him some gas"

Is this (cyclical temperature indications) while driving at a steady speed, stop and go, or idling?
What kind of thermostat did you install?
Can you get some temperature numbers for us? Non-contact IR temp guns can be found pretty cheap these days.
Oh, and how well does your fuel gauge work? You could have a gauge, instrument voltage regulator, ground, or circuit board issue.

Most service technicians haven't had to deal with tuning slant sixes in a very long time. Carburetors, solid lifters, and point ignitions can throw them.

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

I had this exact same issue in my '90 Subaru. The temp needle would rise all the way up, stay for a few seconds, then drop back down to a third up and do this periodically within a minute. I pulled the thermostat completely out and now the needle rests at a constant 1/3rd or so up.....

You can also try this:
http://www.slantsix.org/articles/instru ... nt_reg.htm

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'73 Scamp (the girlfriend): 225ci super/6 2BBL conversion (Almost done!)
'90 Subaru, wagon (the wife): H4-cyl 2.2L

1977 Mercedes-Benz 300D, 5cyl diesel(For sale!)

(1) Verify you have the correct engine temp sending unit installed in the head. Different years had different ohm ratings.

(2) Install an aftermarket water temp gauge. Your original gauge may be internally faulty.

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Casually looking for a Clifford hyperpak intake for cheap.

This sounds more like a gauge problem than an actual overheating problem. Do you have any evidence of overheating (boiling radiator spitting hot coolant onto the ground through the overflow hose, etc.)?

The temp senders for the '60-'63 vs. '64-up engines aren't directly interchangeable, so "wrong sender" probably isn't the trouble, but it does sound as if your sender may be faulty and in need of replacement -- unless your fuel gauge is also reading improperly, in which case the trouble is probably in the instrument cluster rather than at the sender.

Removing the thermostat and running without it is a very poor idea. Don't do it.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

First thanks for all the replys and suggestions! Awesome!
Now to address them, .
I am working to fix it correctly and not temporarily, I know that in an emergency adding water wetter and removing the thermostat can alleviate an overheating problem for the short term but they are no long term fix. Radiators, thermostats and cooling are designed to do a job and I want to restore them to full functionality.
When I drove the car home about 20 miles the temp needle was at the high end of the gauge, not pegged but right at or above the highest acceptable marking. I did not get any collapsed hoses or spewing coolant from the closed radiator cap or overflow.
I drove the car no more than a mile up a slight hill and the needle went high. I turned around and headed back home in fear while the needle dropped down back to a more acceptable level. I drove back up the hill and the gauge went up high but I drove around another mile or so and the needle stayed at the upper level of normal moving down cooler a bit.
I recently replaced the warped exhaust manifold with a new one and I also repaired the broken studs on the ends of the manifold. One stud needed a helicoil as it was having coolant come out as steam. I removed the two studs and sealed them with thread sealant and so far no leaking of coolant.
I have suspicions regarding the gauges because of their age of course. With a full tank the fuel gauge reads closer to ¾ of a tank, while the ammeter tends to pulse at speed and when the engine is revved up. The ammeter should not be connected to the Voltage regulator for the dash instrument cluster but the fuel gauge should since it needs a steady reference.
I will be purchasing a set of meters for the temp and oil pressure so that I can check whether or not the stock meter is accurate and will post results here.
Last question, once I get the freeze plugs back in after cleaning the rust I can get out, what should I use to purge the remaining rust before getting the radiator cleaned out?
Thanks!
John

_________________
Psychics will soon lead dogs to your body!

1963 Dodge Dart 270 convertible

Before you buy and install new gauges (many of which are cheaply-made Chinese gauge-shaped toys that are less accurate than a stopped watch which at least tells correct time twice a day), do some diagnosis. Get a kitchen/candy thermometer and run the engine with the radiator cap loose until the gauge indicates an overheat condition, then remove the radiator cap and put the thermometer in the radiator top tank so it's touching coolant but not metal. See what it has to say. If it's in the 170° to 190° range or thereabouts, you're not overheating. Let us know what you see.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dont have a cooking thermometer, do have a Fluke meter with a thermocouple.
I will check it out and let you know the results!
Cheers.
John

_________________
Psychics will soon lead dogs to your body!

1963 Dodge Dart 270 convertible

You can do the same trick with the thermostat. Drop it into a pan of water and bring it to a boil. If it opens, then it is good, otherwise...

I have also noticed that if the voltage drops for the instruments, the temp gauge will rise. So check your electrical connections.

Thanks much. I put the freeze plugs in tonight and will let the sealant cure and fire it up afterwards and check the temp and voltages on the instrument cluster and let you know waht I find.
Would certainly be nice to have it not being overheating at all, but the stress of watching that needle climb certainly made my wavy gray hair straighten out a bit!

_________________
Psychics will soon lead dogs to your body!

1963 Dodge Dart 270 convertible

Another thing to check for is a loose waterpump impeller. Had this happen on a 66 170. The impeller still turned with the shaft and gave me temp readings higher than normal, then normal . sometimes enough to push coolant out the over flow. Just a thought.........

Is it possible to have air pockets in a slant motor? I know they don't take any special bleeding procedure, but if the gauges are accurate, (if) then that seems to be symptomatic of an air pocket.. which I didn't think slants were prone to at all. My first guess is electrical.

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63 Valiant 200
64 Dart 270
73 Fury II
84 Cherokee 2 dr
86 Dodge W-150
73 Volvo 144
74 Volvo 145
81 Volvo 245

Yeah I had that thought also. I did the refill of coolant and opened the heater wide open and ran the fan and got heat. Then ran the car for a while and rechecked level and did this a couple of times till checking showed a full level.
Thanks for the thought!

_________________
Psychics will soon lead dogs to your body!

1963 Dodge Dart 270 convertible

Voltage limiters can get flaky, but your fuel gauge would go up &down with the temperature gauge too. I bought a radiator cap with a built-in mechanical temperature gauge from JCWhitney; works fine and it gives me a simple way to check the coolant temperature.

If you're really running hot, I'd suggest you look for a pressure leak; even a small leak that doesn't loose much coolant can cause big problems, and it could be intermittent. I've seen air pockets in Mopars after I've changed coolant, but they always got flushed out pretty quickly. Next, I'd make sure you have enough air flow; a missing radiator shroud or bad viscous coupler on the fan can also cause problems too.