1951 Dodge Coronet Engine Coolant Problem

[Dodge51coronet]

Recently purchased a '51 Coronet with a flat head six. It was driveable, however after years of maintenance neglect, I began the process of replacing the engine coolant fluid as well as all of the hoses, clamps, etc. Prior to doing any of this work, I noticed that the temperature gauge was showing that the engine was running slightly hot. I chalked this up to weak, neglected coolant. I drained the old coolant and added a container of coolant system cleaner along with water to help remove any old dirt and sludge,and ran the engine. As expected, after draining the fluid, it came out fairly dirty with some of the sludge and dirt removed. I then flushed the radiator, reversed flushed the block, and put in a new thermostat. It is at this point where I am having the problem! When I tried to fill the radiator with new, fresh coolant it only allows me to put in approximately 5 quarts of coolant. The specifications call for 15 quarts of coolant/water mix. Apparently it is only allowing me to fill the radiator and there is no other liquid traveling any further into the block. I tried starting the engine hoping that the fluid with travel through into the block but to no avail. After five minutes the gauge showed that it was running very hot and then I shut it down. After a while, some of the fluid eventually ran out of the overflow on to the ground. Can anyone please give me some advice as to what might be the problem? I am by no means a master mechanic, however it is obvious that I am doing something incorrect but I can't seem to figure it out! Is there a reason why it will only take a third of it's fluid capacity? Although the engine was originally running hot, the water pump was obvious working properly prior to draining the original coolant. The car never overheated. It just ran a little hot according to the gauge. I just assumed that this was happening due to the years of neglect. I know that running a little hot is quite common with these cars. I used to own the same model/year car and although it used to run slightly hot, I never had any of these issues occur with not being able to add the proper amount of coolant.

I am certain that I am missing something here and I was hoping that some of the more experienced Mopar guys out there can help me out? Thanks!

[Reg Evans]

Could you have installed your new thermostat upside down ? The spring goes down towards the block.

[22touring]

The Chrysler flathead 6 contains a water distribution tube or jacket which will rust out, and when it does it can block the coolant passages in the block, or simply prevent the coolant from circulating. Of course I can't be sure that's your problem, but it sounds like it. We used to always replace the w.d. jacket when we'd overhaul a flathead because they were rusted out. Originally they were made from brass, but that led to electrolytic corrosion where it came in contact with the iron block, so modern replacements are made from ferrous metal. You can replace the water distribution tube after pulling the water pump and radiator.

[jpage]

I don't know if you can install the stat upside down due to clearance issues in the outlet casting, but that's a good start. You may have dislodged some heavy debris that's plugging the flow. Also, those engines have a water distribution tube that runs the length of the block which may have rotted and is now blocking the flow. You should remove the water pump and remove the tube; it probably needs replaced anyway and is necessary for proper engine cooling. The tube can be a real pain to remove but are not an expensive repair. You may also have to remove the freeze plugs from the block to further clean out the water jacket. If your engine is highly corroded, this is the only way to satisfactorily clean it.

[Dodge51coronet]

Thanks for all the advice. I am certain that I installed the thermostat properly. It does sound like it may be a water distribution tube issue. It may be just clogged or more than likely corroded. Besides removing the water pump, will I need to remove the radiator as well in order to gain access to the tube? I will first try removing the freeze plug and try flushing that out to see if this helps. I see one freeze plug on the right (drivers side) of the block. Are there any others? I have a suspicion that I will still need to replace the water distribution tube.

[JACK M]

A proper cleaning is a messy job.

There should be more than one core plug (there really is no such thing as a freeze plug, but we know what is being referred to).

Get an old coat hanger and a high pressure hose and start digging out the sludge. Rinse and repeat. Several times.

The distribution tube is the length of the engine so you will need to at least take the radiator out as well as the water pump. Hope that the grill will leave enough room to get it out. (and the new one installed)

When you are satisfied that you have the block cleaned out install the new distribution tube then new core plugs and fill with water first and test run.

If there are no leaks and no over heat then drain and put in your antifreeze and you should be good to go for years.

[jpage]

There maybe at least 3 on the left side. Look closely at my avatar and you can see them. While this is a '36 engine, the blocks should be basically the same.

Edited October 17, 2015 by jpage (see edit history)