318 Water Pump Bolt That "Always Wants to Leak" Story

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dibbons

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I know this is a mysterious but common problem and wanted to document my personal experience (for all posterity) with the bolt that serves to hold the bracket to adjust the alternator on one end and also serves to secure the water pump.

The subject powerplant is a circa 1980 318 block that was rebuilt professionally about 10 years ago using a cast iron 273 water pump (vehicle is '65 Formula S). The last three years the vehicle was being restored, so the engine has not run during that time. I had removed the water pump, cleaned and painted it, and reinstalled it with new gasket, of course.

When I first tried to re-fill the coolant for the first start after restoration, the bolt in question began to leak as soon as I began to fill the system with the second gallon of coolant. I remembered having put a good quantity of brown, sticky Permatex on the bolt threads (including the other 3 bolts that pass into the water jacket) so I was surprised to find a drip. The bolt was already good and tight, but I tightened it further still. No change, still dripped.

OK, I removed the bolt which measured a hair more than four inches. I purchased a new, longer bolt at 4 1/2 inches and coated the threads heavily with the Permatex (which I have been using since the 1970's by the way). Now with even more thread contact and fresh sealant I was sure it was good to go. I even waited a day or two for the sealant to set-up a little more. Same story, as the second gallon of coolant was added, the drip ... drip returned. The more coolant I added, the more it dripped.

I had anticipated a repeat problem like this and had therefore purchased a little tube of aluminized powder sold to stop radiator leaks (this tube had a yellow label with the "Gunk" name). I had used a similar product called "Alumaseal" years ago and had success with it. I started the engine and let it idle while I topped off the coolant level and poured in the aluminum powder concoction. By now the bolt in question was not dripping, it was pouring out in a little steady stream. I could hardly believe how much coolant was passing by and around that bolt! And even worse, I could not and cannot envision how the coolant finds its way out so easily.

I ran the engine for about ten minutes and the stream seemed to have diminished to a drip again. I ran the engine even longer and even the drips seemed to stop (got it to about 190-200 degrees on the aftermarket mechanical temperature gauge). Now, I don't particularly like to "repair" leaks of any kind in such a fashion, but I was in no mood to dis-assemble the front half of the engine today. What was I going to find if I had done so? Well, if and when the leak returns I won't have any choice and I will take it apart and investigate. For now, it's fingers crossed.

And I forgot to mention: I found a tiny puddle of coolant about the size of a nickel on the intake manifold directly under the thermostat housing (so what else is new?) I had taken great pains to clean those surfaces, use a gasket with a very minimum coat of sealer (The Right Stuff), and made sure to torque the two fasteners equally over several stages of back and forth. I dried that area with a rag about three times as it kept coming back. Much later, after I had evidently stopped the bolt leak, I checked again and the puddle was "gone". Did it stop leaking on its own, with the help of the stop leak powder, or did the tiny bit of coolant just evaporate as the intake manifold became hotter and hotter? I can't say. I was not going to tighten the bolts any more until I found how it was going to proceed. Sometimes those little seeps do plug themselves up after a short time.

The amount of coolant loss was maybe a quart or more (see photo).

leaky bolt.png
 
Wow! That long winded story and all we get is a picture of antifreeze in a drain bowl and 1/2 on the floor? Lol!
We deserve more photos after that story.
 
I use rtv, permatex brand, but black rtv is what I use on bolt threads into water, and or thermostat housing gaskets. I never use blue. Copper rtv is what I use on exhaust/header gaskets,ball collectors etc.
If the bolt holes are rusted, that's your problem. You probably know that though.

Now 'Permatack' does not work well with water sealing in my experience. I use permatack for oil sealing.. like pans & covers. Just to put it out there..

"The right stuff" works on most anything.

Probably leaked by your hose clamp on the intake.
 
You want to be CAREFUL with Mopar water pump bolts and CHECK CAREFULLY their length and position. I cannot remember "which one" (one of the shorter/ lower bolts) if it's a bit too long it can screw right through the block and tighten AGAINST THE CYLINDER SKIRT and crack the cylinder
 
Just did a water pump bolt on the lower drivers side one. Pulled it out and found the bolt threads were only in an 1/8”. Like a thread and a half. Made a new bolt (cut down a longer bolt and re-threaded it.grade8) then cleaned the hole with brake clean- let it dry and rtv on the threads and tightened down. I let it sit a day before I added coolant and pressure. Seems good now.
 
If you want leak free operation, use proper thread sealant.....which is for sealing threads. Yet to find anything better than Loctite 567 thread sealant.
 
I was just thinking, why this bolt and not the other three similar water pump bolts? Well, being the fact this one gets tightened and loosened many times over the years while adjusting the alternator belt, maybe the threads get "worn" more so than the other bolts that are not disturbed? Must be a logical explanation out there somewhere.
 
You are not gonna wear out threads, BUT they can rust and deteriorate, they can be overtightened and damaged, especially if one that had been in there was too short. Thread chasers/ taps are always good to have. There are three popular types of taps, and many hardware stores don't know squat. A "normal" tap is often characterized as being a 'starting' tap as it is somewhat tapered. A plug tap is straight all the way, and a "bottom" tap as the name implies, is able to tap closer to the bottom of a hole
 
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