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I had my radiator re-cord about a month ago. Last week we took it on about a 100 mile drive. We made a stop and I stayed in the car and let it idle. The gauge went way up but as soon as I started driving it cooled back down.I had lost about 1/2 gallon of anti freeze. I put a new thermostat in thinking maybe the old one stuck.I filled it again and took a short run. When I pulled back into the garage the temp started going up. Looking underneath the car I had anti freeze all over the under side of the car from the radiator forward.Is there a sure sign the water pump is bad or a sure sign of blown head gasket? Thanks Bob

Was it burping out coolant when you pulled into the garage causing the mess?
If the water pump is leaking coolant will be coming out of the weep holes on the bottom of the pump casting.
Are you overfilling the radiator? When cold the coolant should be way at the bottom of the radiator top tank. When hot it will expand to about 3" below the top.
Are the hose connections leaking? A bad head gasket is very unlikely.

I'm not sure if it was just when sitting or not.It was all over the front like it was spraying. It was even behind the bumper.I don't see anything from the weep holes and I did not see any foaming in the oil. I had added coolant to about the half way point of the radiator top tank. I did take out the radiator again and am bringing it back to have it pressure tested again.This is the only time I hope there is a hole in it. Thanks

Your problem is "after boil" caused by low coolant flow to an engine hot spot. Most often that hot spot is the rear cylinders next to the firewall. Crud in the cooling passages in the block/head is likely. Have the radiator shop back flow the radiator to check for crud. If none is found then check the water pump for corroded fins on the impeller. Likely it will be necessary to flush out the block/head with as much probing with wire and tools to fluidize the crud so it can be removed.

Hi Bob.

Try looking up info, on your problem, by using the "SEARCH" function of our chat site. We have posts going back around ten years. Your topic is one we have discussed several times. Below is a link to some posts I have made on the topic. Like you, I am hoping yours is a radiator problem.

Good luck, Mike

Overheating Issue

14 1/2 years... but who's counting?

After you click on SEARCH, be sure to click on the ADVANCED SEARCH TIPS link. It will really help you find stuff better.

Thanks for directing me to the site. Good advice. I did pull the radiator out and brought it back to the guy who record it. He check for leaks while I was there and found none. He kept it to flush and dry out. I also checked the water pump and it seems good. After I put the radiator back in I'm going to take it to a friend of mine and he's going to shave the head and put a new head gasket in. Thanks again-Bob

Bob,

Before you install a new head gasket I suggest you do the following:

a. Take the thermostat out.
b. Put the thermostat housing back on.
c. Trip the fan belt.
d. Fill with water to the top of the thermostat housing.
e. Crank up the engine and look for bubbles at the thermostat housing opening. There should be no bubbles or movement of the water. If that is the case, you don't need a head gasket.

About the block:

a. Take out the drain plug on the left rear of the block.
b. Take out the thermostat and replace the housing. Leave top radiator hose off.
c. Put a garden house in the top of the radiator.
d. Using a high air pressure blow back through the block until the water clears up. The wire is a good thing but want do much.

About the Water Pump:

a. If it is not leaking, it is more than likely just fine.
b. The only failure with water pumps is failure at the seals. That causes it to leak.

About the level of the water in the top tank. You don't want to fill it more than expansion will allow. Gene is about right about that.

Good luck,
Charlie

Thanks Charlie

To add to
charlies good advise completely remove the cooland drain cock on the left rear side of the block. Then take a piece of coat hanger wire and probe into the opening as far as you can to dislodge and rust that has setteled in that area.
Removing the head just to clean out the piles of rust in the head passages and down into the block will help also.