70 sierra Grande overheating

[ls70918]

I'm new to this forum and not a very good mechanic. That being said, I recently picked up a 2WD 1970 Sierra Grande 1/2 ton with the 402. One day it overheated (It just has a warning light on the dash- no gauges yet). I probably let it get too hot trying to get home.

Any way, since then I have replaced the thermostat and had the original radiator rebuilt. I refilled the radiator, ran it for a while, topped it off and it ran cool for several days. Then it started overheating again. The coolant level was down and I had to add between 1/2 gal. to a gallon.

The engine oil continues to look good and there are no leaks. Is there some way that coolant could be going into the intake manifold and being burned? What would be the fix. Anyone have any ideas?

I've looked at some old threads here for answers, but didn't find one.

Thanks in advance for your comments. And I'm sure I'll have a ton of other stupid questions in the month/years to come.

[71K20chevy]

Probably a bad head gasket. With the engine cold, start it up without the radiator cap and see if bubbles are in the radiator. If so, it's a bad head gasket.

[Stocker]

Originally Posted by 71K20chevy

Probably a bad head gasket. With the engine cold, start it up without the radiator cap and see if bubbles are in the radiator. If so, it's a bad head gasket.

This sounds like a good possibility & a great place to start looking.

Originally Posted by ls70918

Is there some way that coolant could be going into the intake manifold and being burned?

Could be, or directly into a combustion chamber if it's a blown head gasket.

The only stupid question is one that doesn't get asked. There's a vast amount of knowledge here and lots of people ready to help. Welcome to the best board anywhere, and congrats on your new truck!

[MusicMan70]

Welcome ls70918 and good luck with the overheating issue. Now how's about some pics....

[leftybass209]

Antifreeze being burned is the only explanation, if the oil is clean and there's no leaks. That's a lot of coolant being burned though! Id think the exhaust smoke would be white as well. Best case would be blown head gasket. Worst case, cracked head/s. Good luck!
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[hugger6933]

How many times has it been low? It is normal for a person without much experiance to have a low coolant level after changing a radiator and refilling not getting full because he has not waited for the truck to reach operating temp to fill to the proper level. Bubbles in the radiator or water coming out the pipes or white smoke upon acceleration , or oil turning into a very unappetizing milkshake in the oil pan or the dipstick that is bad as well. I would hope that it did it for you only that one time and then upon refill you solved your problem and now can drive that big block for 100, thousand trouble free miles at 22 miles per gallon. Hey it is Christmas!! Jim

[stsalvage]

this is nothing about your problem But if you have a AC truck it might be a little harder then a truck with just a heater core But my old grand pappy always told me if your going to drive anything you need 3 things working for you before you drive any thing.1 Good brakes,2 all your lights and blinkers all working. 3 and a Good Heater core..I ask him why a good heater core or heater its summer.

Word to the wise when the truck over heats turn on the heater.On a 102 degree day your truck over heats you fry. You start feeling the truck running rough and your gauge or warring light comes on turn on the heater.It will give you 30 seconds for that water to go throw the heater core and drop by 50 degree's and even tho your frying your not standing on the side of the road frying and knowing you will be Paying for a tow.

He said the heater core will save you time and again in any car truck on the planet you over heat give that water 30 seconds it will change your life.

see your heater core is like another radiator it takes the heat out of the water.

even tho its a 102 out side switch the defroster on open your vent windows and the heat should not bother you to much

[ls70918]

Thanks for the replies. I'll check into the head gasket issue first.

[towbar]

if its a head gasket\cracked head, you'll have the tail tail steam out the exhaust that never stops......at least until you run out of coolant. Also you'll have the sweet smell of coolant out back if your running anti-freeze. You should be able to do a compression check or a leak down test to determine if its a head issue. Heater core signs could be coolant in the PS floor board, smell of anti freeze inside, heavy windshield steam/fog with the defroster on.