Hi all,
My slant6 overheats. I am using a new, bigger fan as well as oil cooler, but it cannot keep the temperature down in traffic/slow driving. I am getting a water pump and have a new radiator I can try. However It's the water jackets in the head that I am concerned about now.

Attached is a picture of the head, where the thermostat sits. I ran a pump and used the cleaning solution (mukowt brand) through it. However it doesn't seem to have done much: There is just so uch build up in there.

I have reviewed some other threads, such as
viewtopic.php?f=19&t=62549
viewtopic.php?f=19&t=62601&hilit=cooling
viewtopic.php?f=19&t=61750&hilit=head+cleaning
viewtopic.php?f=19&t=63183

Other than engine disassembly, which I cannot budget for, what other options do I have to clean it up?

Thanks, Dallas

What kind of fan are you running? How many blades? Is it in a car or truck. If you have a bunch of junk in the block / head that is moving around in the system it probably has clogged up the radiator.

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Does the lower hose have a spring in it?

Does your water pump still have vanes on it?

It is odd that your engine only overheats at low speeds/loads. That would indicate that there isn't enough air flow through the rad at low speeds. Is the fan installed correctly? What is the temperature rating your thermostat? Have you checked your ignition timing and made sure that the advance mechanisms are working properly?

The rust & scale build-up in your engine would reduce heat transfer into the water jacket, potentially causing issues like pinging but I don't think it would cause your engine to run hot at low speeds. I've had my impeller break loose from the pump shaft but, if unless your water pump is leaking, I don't think a new water pump is necessary.

Specifically, what is happening when you say that you can't keep the temperature down in traffic/slow driving? Does it eventually boil-over?


I would use a citric or oxalic acid solution to clean your internal surfaces. I've used 1 kg of citric acid from a local wine supply store in my engine and run the engine for day or two with this solution. You might need more than one cleaning to get all of the rust & scale. Take care to flush the acid solution out well before filling with a 50% ethylene glycol solution. See Cooling System.

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1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

Hi all,

Thanks for all your replies so far I hope I can answer all your queries in one message:

My vehicle is the AP6 Sedan (car) and the fan is a new SPAL brand, 16" fan with many curvy blades in there. It pulls from behind the radiator and should be up to 2000cfm. It is however installed offset on the Radiator, as the pump assembly and fan engine do not have enough clearance. This means there's a section of radiator that is not covered by the fan at all
I don't know if it's possible, but a shroud could be setup to help.

Thermostat is 180 standard. I tested it with hot water from the kettle and works fine.

The lower end hose does have a spring, though it's rusty and has build up. I'm replacing that. The water pump looks ok, just a bit of wear showing. The thermostat housing does however have quite a lot of pitting inside. The pump and housing is to be replaced. I think my radiator is pretty clean, however I have a new one if this is not good enough.

I haven't had it boil over, but my overflow tank gets very full. I am going to try cleaning the head for longer, hopefully if that part of the system is as good as possible, then I can continue to work on the radiator/fan assembly to eliminate the rest of the issue.

Dallas