I posted this in "What have you done to your truck today", but haven't gotten any response. Knowing how helpful and knowledgeable you'uns are, that puzzled me until I realized two things: First, that wasn't the thread in which to ask the question, but more importantly that I'd unwittingly posted in the midst of the responses to one of our faithful's posts regarding his "I'll do anything to help a young damsel in distress". Even I forgot about my plight as I pondered his. So, here goes......

After the overheating incident 3 weeks ago I haven't had a chance to drive the truck much until today, and the couple of times that I did drive it the radiator seemed to need a bit more coolant. Today we took it to "the big city" shopping and drove it ~60 miles. When we started out the system was full and the overflow tank half full. On the highway the temp stayed between the C and the bottom of the NORMAL range, but when we got into stop and go traffic it climbed to the O and then back down to close to C.

When it cooled down for an hour I checked and the radiator needed a quart as did the overflow tank. But, on the way home it did the same thing when we slowed down, and when we pulled into the drive it was gurgling at the 'stat and spitting steam into the overflow. And, when it had cooled it was down again both places.

Thoughts? Mine aren't fit to type.

What are the weak points on a 351W? Block? Heads?

What are the best testing procedures? Lead-down of each cylinder watching/listening to the radiator awa intake and exhaust? Putting pressure, albeit ~15 psi, into the radiator and listening/feeling at spark plug holes, dip stick, etc?

Signed,
Gloomy

 

Have you changed the thermostat since "the overheating incident"?

Thermostats can fail if overheated. They can fail closed, or fail partly open. They also make "fail safe" thermostats that are designed to fully open when they fail.

My son's car with a 195 thermostat would run about 160 on a cool day, 180 on a warm day, and it would hit 220 on a hot day, hotter in traffic. Pulled the thermostat and it was stuck about 1/4 open. I installed a new thermostat and now it runs 195 to 200 at all times.

 

See if your local oreilly has a cooling system pressure tester you can rent. Fill the cooling system, and build pressure on it. Walk away for a bit. When you return, if the pressure has dropped, there should be signs of where the coolant went. If no external leaks, then start thinking head gasket, cracked head or block. Gasket is more likely though.

 

Check your freeze plugs lately?

Could be a rad that is blocked up. I had very similar problems with a truck until the whole side wall of the radiator blew up. replaced it and temps were fine after that.

 

Good idea about the 'stat. I'll change it out yet again. And, while I'm at it, will swap the temp sensor awa test the wiring to it.

As for the tester from O'Reilly, I'll do that as well. Easier than making one and I haven't seen my friends there in some time.

On the rad, the "new" truck's is half again as thick, so eventually it'll go out to be boiled/rodded and be put in. However, the truck didn't have prob's before that fateful day, so for now I'm thinking this one isn't too bad. Agree?

 

I agree to check all the spark plugs, to see if you have a head gasket leak. Because if you are loosing that much coolant it has to be going somewhere, either it is evaporating or going out your exhaust.

 

I neglected to say THANKS previously, but I do thank all of you for your help. And, I will be checking the plugs to see if there's any indication of which cylinder, if any, is getting drenched.

However, I don't think I'll be able to do this for a couple of weeks since I'm heavily involved with our sun room build and the wife is pushing to get it done. (Actually, I'm pushing as much as she but it feels better to blame someone else.) Anyway, thanks!

 

Today I finally got to do some testing - in a couple of ways. First, I drove the truck after having filled the cooling system completely, making sure that all the air was out. When I got home I observed it closely while it cooled, and bubbles continued to come into the coolant recovery tank for 10 to 15 minutes, which implies leakage from a cylinder.

Then I put a cooling system pressure tester on the radiator. Sure enough, it leaks. Slowly, but surely. And, it must be leaking internally as there aren't any signs on the outside.

So, I'm thinking about the next steps. When I get the time I can put the tester on for an extended period and pull the plugs to see if I can tell which cylinder is getting the water. Or, I could put 100 psi into the cylinders, one at a time, and see if one leaks into the cooling system.

In any event, it looks like the heads are coming off at a minimum. I'm considering pulling the engine to put it on the stand to make things easier. Send the heads off to be pressure checked and, while waiting for them, check out the bores for scoring. And, pull the pan to fix the rear main leak and, while in there, pull the rod and main caps to check for scoring.

On the other hand, the rear main isn't leaking much, and I've had the heads off while the engine was in the truck. So, maybe pulling the engine is a bit much.

Thoughts?

 

Leak-down test.

I use the host from a friend's compression tester, remove the gauge and hook it up to an air compressor.

Put each piston to TDC, fill the cylinder with air (30 lbs should be sufficient), look for bubbles in the radiator/listen for air out the carb/exhaust/oil fill hole.

Obviously, do one cylinder at a time.

 

Basically the same, but I'd use the leak-down tester I made. It has a .060" orifice with gauges either side of the orifice. Any leakage shows up as a pressure drop, and since I have 100 psi in, the drop can be thought of as a percentage.