1979 Chevy C10 Coolant Leak

[derekj]

I just bought a 1979 Chevy C10 with the GM inline six engine and it ran well around town until I drove it for an hour and a half on the highway when I got the temp warning. I pulled over and took a look and there was definitely a coolant leak on the left side of the engine (if you're looking at the grill) and some in the little channel at the bottom of the radiator. Once I shut it off a bunch of the coolant from the reservoir got pulled into the radiator. I let it cool down for awhile and filled the coolant tank back up until it was full and attempted to drive back home. On my way home the temp light came on again and I pulled over and again when I turned it off a ton of the coolant got pulled from the reservoir to the radiator but the reservoir was just as full as when I had filled it up before driving home.

My thought now is that there's definitely a leak somewhere that I have to track down but is there anything else I should be looking into like the water pump or freeze plugs or anything? This is my first time with any of these older engines.

Thanks!

 

[squaredeal91]

I would start with the leak. And make sure your not losing anymore fluids and then go back on some test drives. I know you said warning light came on but what did your temperature gsuge read ?

 

[derekj]

Unfortunately mine doesn't have the gauge just the light so I have no idea what the actual temperature was

 

[75gmck25]

Since you don’t have a temp gauge, I recommend buying a mechanical gauge similar to this one and mounting it under the dash. https://www.summitracing.com/parts/atm-2333

You could also buy an electrical gauge, but then you have two parts to worry about. Sending units go bad, wires gets shorted , etc.
Mechanical gauge makes it harder to route the line through the firewall because of the probe on the end, but once installed it doesn’t even need electricity. It just works all the time.

 

[derekj]

Thanks for all the help! I was looking at replacing the radiator hoses to see if they were leaking and was trying to figure out which ones I needed and saw this on the low side radiator hose. I have no idea what it is so any help would be appreciated!

 

[squaredeal91]

Looks like an Aftermarket inline block heater. Follow those wires. Should be a 110 end on it

 

[Rickf]

I've had good luck finding leaks with dye and a UV light and/or a radiator pressure testing kit.

 

[75gmck25]

You mentioned that you “filled” the expansion tank. Did you just fill it up to the cool line with the engine cool? Most of the time with a cool engine the tank is only about 1/3 full, and then coolant fills it more as the radiator gets hot. As it cools it will pull coolant back into the radiator.

Start with some basic mechanic work. Replace the thermostat with a new one (GM probably used a 195), and check the tension on the fan belt. Make sure the fan is working effectively and the radiator is not blocked (use your garden hose to spray through the fins and clean out any blockage). Drain and flush the system, and refill with a 50% antifreeze solution. As already mentioned above, you can borrow one of the pressure testers from Autozone to do better testing.

Note: You can also do your initial testing with only water, but long term you will get corrosion, and at the first big freeze you will be replacing your broken radiator or hoses.

Since you have no temp gauge, buy or borrow an infrared thermometer and start checking temperatures. You need to at least get a baseline for water temp in and out of the radiator so you know if you are making any progress.

General troubleshooting
- overheating at highway speeds usually means a blocked radiator and/or very poor coolant flow, since you have plenty of air flowing
- overheating at idle speeds usually comes from poor fan air flow (slipping belt, backward fan, blocked grill) if the radiator is functioning properly

 

[Rickf]

I don't see a fan shroud.

 

[derekj]

You mentioned that you “filled” the expansion tank. Did you just fill it up to the cool line with the engine cool? Most of the time with a cool engine the tank is only about 1/3 full, and then coolant fills it more as the radiator gets hot. As it cools it will pull coolant back into the radiator.

Start with some basic mechanic work. Replace the thermostat with a new one (GM probably used a 195), and check the tension on the fan belt. Make sure the fan is working effectively and the radiator is not blocked (use your garden hose to spray through the fins and clean out any blockage). Drain and flush the system, and refill with a 50% antifreeze solution. As already mentioned above, you can borrow one of the pressure testers from Autozone to do better testing.

Note: You can also do your initial testing with only water, but long term you will get corrosion, and at the first big freeze you will be replacing your broken radiator or hoses.

Since you have no temp gauge, buy or borrow an infrared thermometer and start checking temperatures. You need to at least get a baseline for water temp in and out of the radiator so you know if you are making any progress.

General troubleshooting
- overheating at highway speeds usually means a blocked radiator and/or very poor coolant flow, since you have plenty of air flowing
- overheating at idle speeds usually comes from poor fan air flow (slipping belt, backward fan, blocked grill) if the radiator is functioning properly

Thanks so much for all this! I filled it up while the engine was cool and I filled the expansion tank up about 2/3 of the way, it was definitely past the cool line. When I stopped again after that the expansion tank was still at the same level as when I had filled it earlier and then it drained into the radiator back down to about the cool line.

I'll pick up a new thermostat and replace that. I took a look at the radiator and it doesn't look like it's blocked at all at least in the fins. I'll grab one of the pressure testers as well and give that a go.

 

[derekj]

Ok so I replaced the thermostat and the upper hose since that was leaking a bit when I first pressure tested it. I pressure tested again after that and no leaks anywhere. Do I need to burp it or anything to get rid of the air in the system from replacing the hose?

I drove it around the block afterward and the two hoses into the water pump were fairly hot after the little spin. Is that normal?