70 Challenger 318 overheating/boiling

[Bones54]

Hey all, just joined and this is my first time posting to the forum, so be forgiving if this is in the wrong location..

Picked up my first Challenger last Saturday and almost have it on the road again, but I've got a little bit of a head scratcher. my 318 is overheating (starts to overpressurize/boil after just a few minutes of running), I'll give as much info as I can, so it'll be a long post.

I started working on the cooling system Thursday night after work (an automotive repair shop in Oregon). The PO had straight water in it, so I changed it, and at the same time put a new water pump, hoses, thermostat, radiator cap, and flushed out the radiator. The heater hose port on the w-pump was completely clogged with crusty coolant, so that wasn't a good sign.. took it for a test drive to find out it's overheating. Heater core is leaking too, but that's a separate issue. Got home, bypassed the heater core and pulled up the intake to check the passages. No blockage, so put it back down. Tried another thermostat (180*) with a hole drilled in it and used a vacuum filler to check for further leaks/fill it. None found, so filled it with 50/50. Test drive again, still boiling. Tested cap, good, and thermostat is opening. Placed a rag in front of the radiator and it stuck so I have good air flow through the fins. Water pump is pumping, and heat is being pulled out of the radiator. Used a temp gun to measure temp at various spots and found that it'll start to boil when the t-stat housing only reads about 130*.  Checked #1 and #2 cylinder temps at the front of the heads, #1 approx 177*, #2 approx 235*.

its acting like I've got air stuck in the block somewhere, based on the early boiling temp. My main question is: since the coolant was so nasty, and still looks pretty bad after changing it twice, does it sound like I've got a bunch of sediment buildup around #2 cylinder walls causing a hot spot? I'd really rather not pull the heads, but if it comes down to it, whatever.. any other ideas would be greatly appreciated, thanks!

[734406pk]

Welcome to the site!
 Rusty/dirty coolant can clog the radiator/head gasket passages etc. Check your base timing first. Is this a stock 318?

[Bones54]

That's what I'm thinking, that the passages in the coolant ports on the head are plugged. Based on how much rust and junk came out of the radiator came out, that wouldn't surprise me at all... The radiator seemed to have plenty of flow through it when I flushed it out this morning, and the fan seems to be pulling a fair amount of heat out of the fins, so I don't think the radiator is an issue. Especially since it starts to boil before the t-stat even opens up (starts purging out the overflow around 130*).  Most likely I'll pull it back out had have it cored anyway, just for peace of mind. Forgot to mention that I did do a block test on it as well, and it passed. I also have a chemical flush treatment in it that I'm going to let sit in it overnight, so we'll see if that helps out with anything.

From what I was told when I bought it, it's just a stock 318, and original 727 trans. It was rebuilt in the mid 80's due to a broken timing chain, but the owners didn't say that they put any modifications in it. I haven't checked the timing, the lady that I bought it from (2nd owner since 1972) told me that the balancer had spun slightly, and I haven't taken the time to pull #1 plug and mark where TDC actually is with a paint pen. Should be around 10*? It doesn't kick back on me at all while cranking, so it shouldn't be too far off if it is. I'll stop by the shop tomorrow and grab a timing light (my 40 year old Suntune here at the house finally gave out, and Snap-On won't warranty my old light from the early 60's    ...)

Can the base timing cause that much of an overheat even after just a few minutes of running? What gets me is the temp difference between bank 1 and bank 2 heads. That's why I'm leading more towards a clogged passage in the one head..

Thanks!

[734406pk]

The base timing for a '72 318 is TDC according to my manual. If the timing is off, anything is possible. Check your balancer for accuracy with a piston stop. If this engine sat for a long time with straight water in it, rust may well be the issue. You will need a strong chemical cleaner and/or back flushing. Removing a few freeze plugs can help to let out the heavy sediment, plus you can see whats inside the coolant passages. Post back your findings. Good luck!

[734406pk]

 I have used this product in the past and it worked well. The only downside, it's NOT FRIENDLY with aluminum parts (timing chain cover, water pump,heater core etc.)

https://www.permatex.com/products/cleaners-degreasers/parts-cleaners/permatex-heavy-duty-radiator-cleaner/

[Bones54]

Thanks for the link to the flush treatment, maybe I'll give it a try if this next flush doesn't seem to be breaking up anything. I might pop in a new freeze plug on the front side of the head, too, just to see the coolant passages.

Flushed out the radiator again, along with the block until I got clear water. Pulled out the thermostat, added another treatment and am letting that sit for a while.. Checked timing, the balancer was actually dead on 0*, so I'm not sure why the last "mechanic" to do a tune up said it had spun..

Maybe I shouldn't be bagging on other mechanics, because me, being a mechanic, seemed to have missed a key bit of information.. When I pulled out the thermostat, I left the radiator cap off to bleed the air out of the system again. I remember seeing coolant flow yesterday, but with the cap off today I didn't see any water flowing through the top tank.. I read in a few different threads that there is the possibility of the fins on the water pump being incorrect (one set up for a newer 318 with a serpentine belt). After I let the new flush treatment sit for a while, I'll go grab the original water pump out of the metal bin at work to make sure that they're the correct orientation. I'll keep everyone posted, but boy am I going to feel stupid if that's all that it going on with it..

[734406pk]

Thanks for the link to the flush treatment, maybe I'll give it a try if this next flush doesn't seem to be breaking up anything. I might pop in a new freeze plug on the front side of the head, too, just to see the coolant passages.

Flushed out the radiator again, along with the block until I got clear water. Pulled out the thermostat, added another treatment and am letting that sit for a while.. Checked timing, the balancer was actually dead on 0*, so I'm not sure why the last "mechanic" to do a tune up said it had spun..

Maybe I shouldn't be bagging on other mechanics, because me, being a mechanic, seemed to have missed a key bit of information.. When I pulled out the thermostat, I left the radiator cap off to bleed the air out of the system again. I remember seeing coolant flow yesterday, but with the cap off today I didn't see any water flowing through the top tank.. I read in a few different threads that there is the possibility of the fins on the water pump being incorrect (one set up for a newer 318 with a serpentine belt). After I let the new flush treatment sit for a while, I'll go grab the original water pump out of the metal bin at work to make sure that they're the correct orientation. I'll keep everyone posted, but boy am I going to feel stupid if that's all that it going on with it..

Most of the standard cooling system flush chemicals on the market today are "detergent based" (for good reason)and are safe on aluminum and other soft metals. The down side is the detergent based cleaner has little effect on rust scale.
 Acid based cleaners are effective on rust but attack soft metals like aluminum. Just be careful with this permatex stuff.
 So the timing marks are ok, go ahead and check the timing. The stock 318 spec is 0 degrees or TDC. My manual states NON electronic (point style ignition) for '72. If that's the case, 30 to 32 degrees of dwell angle s called for ( this is important for proper coil satuation).
 Check your water pump carefully. Some serpentine belt driven (Late model) water pumps turn backwards as compared to the earlier Vee belt driven pumps. Check and compare the new and old impeller vanes. 

[DocMel]

The culprit, I'll bet money, is the radiator.   If its stock, its over 47 years old.   Take your radiator to a reputable  rad place and have it looked at

[1 Wild R/T]

 (starts to overpressurize/boil after just a few minutes of running)

When they get over pressurized quickly it's not a plugged cooling system, it's worse.... Likely the plugged cooling system caused the issue but it's not your biggest problem

You work at an automotive repair shop... Ask if you can borrow a block tester....

Another trick to see which bank the problem is on.. Pull the fan belt & remove the Upper radiator hose,  thermostat, & housing... Leave the coolant filled to the height of the thermostat... Start the engine & watch for bubbles, they will come from the side with problems....

Good luck, lets us know what you find...

BTW if you do the block test don't pour the fluid back in the bottle, it will contaminate all the fluid...

[Bones54]

Sorry for the late response, as you know sometimes life happens an projects get pushed to the side...

I did a block test and it passed, so no concerns there. Ended up taking the water pump off again, and while I had it off I rechecked the timing cover ports. The previous owner had the engine rebuilt about 500 miles before she parked it for so long, and the rebuilers used a silicone sealer along with the paper gasket. this caused the port on the passenger side of the block to be restricted to about 20% flow, and while sitting the old coolant clogged what opening was left in the timing cover. Used a screwdriver to clean out all the crusties and silicone, reinstalled the water pump, filled it up and no more overheat! Very thankful that I wasn't dealing with a unsolvable mystery issue, and thanks to everyone who gave input. Now I'm dealing with a fuel boiling concern, but that's an issue for another thread...

Up and on the road again!!