My 72 350 is losing coolant somehow. It was so low after a two hour drive today that the heater stopped working. When I opened the radiator cap, there was no water in sight. The inlet radiator hose was almost empty.

There's no sign of leak from the heater, or from any of the hoses/couplings. The spark plugs are all nice and tan.

My question: can the plugs be tan if I'm burning coolant?

 

Usually the plugs from the cylinder(s) burning coolant look unusually clean.

Sounds like it's time for a pressure test to see if you can find a leak.

- Eric

 

It's amazing how quickly the coolant level can drop with even a very small leak. It only leaks when under pressure, which means while you're driving, making it hard to see. And then since it's so hot, it evaporates quickly instead of leaving puddles.

Get the engine good and hot (highway driving), then stop in a safe and quiet area and shut down the engine. The cooling system pressure will rise even higher, as the heads put their heat into the system but the radiator can't dissipate it, since neither air nor coolant is flowing.

Use your senses (sight, sound, and smell) to find the leak. Common areas are the weep hole on the snout of the water pump (typically indicating its bearing is almost gone) and all around the intake manifold (a mirror and bright light helps to see the back). But of course it could be the radiator, heater core, heater control valve, or a hose as well. And, of course, check your crankcase to make sure the oil's not getting milky, indicating an internal leak.

 

Sounds like what happened to me after my first engine build. The head bolt with the stud for the alternator bracket didn't get torqued properly and my "coolant" was leaking into the cylinder.

At that time, my "coolant" was plain water since it was a new build and I didn't want to waste antifreeze if there was an issue. The plain water didn't make white smoke out the exhaust like antifreeze does, so it wasn't initially obvious that the head gasket was leaking.

 

Well, I'm getting a form of whitish smoke, but it's also freezing over here, so I had put that down to being normal.

The pressure test will definitively tell me whether it's a coolant leak or not? I can do one easily. Second will be to get it hot, shut it off and listen/look/smell for a leak.

Would it make sense to torque down all my head bolts for good measure?

Will the milky oil be visible on the dipstick?

 

Oil will only be visible on the dipstick if coolant is leaking into the oil.

There's no harm in retorquing the head bolts. They're not those fussy European torque-to-yield types.

I would do the pressure test both hot and cold - expansion of the metal can seal a very small leak when the engine warms up.

You should hear a leak even if you don't see one, but (I've never tried this...) you should be able to hear a head gasket leak into a cylinder by removing the spark plug and listening through a tube placed in the spark plug hole.

The cooling system should hold pressure for a good long time, theoretically for over an hour, so if it loses pressure while you watch, you know there's a leak somewhere.

- Eric

 

Alright, then that's the plan, first thing tomorrow.

Along with brakes. >.>

 

You may get lucky and it be only the rad cap lost pressure, it may have pushed most of the coolant into your overflow bottle. Hope for the best !!

 

I don't have an overflow bottle - I have a line running from the rad cap neck down past the tranny cooler line, letting it drip on the ground.

 

Hopefully its just your rad cap maybe their is signs of coolant in the rad cradle of some discolor running down the rad tank .

 

If you're leaking that much into your oil then your oil level should be way over full.

 

i had a bad intake gasket and it was going in the oil pan, drain your oil and see how much fluid comes out

 

Very possible your blowing your coolant out your overflow hose. Especially with an old rad cap.

 

My oil level goes from "full" to "empty" over the course of about 1500 miles. I'd say that's not terribly weird.

Can the overflow drain back INTO the radiator again?

 

You mean it goes from the "FULL" mark to the "ADD" mark on the dipstick, right?
If so, then that means you're using about a quart every 1,500 miles, which is perfectly reasonable, especially for a used engine.

As for the overflow - once it's out that hose and on the road - it ain't comin' back.

- Eric

 

Yes, exactly. The engine has done at least 100k miles, (the odometer is at 63k km, and I suspect it's done at least 160k, if not 260k).

I meant if I installed an overflow bottle - I'm WELL aware that it doesn't magically whisk back up the hose once I park if there isn't a bottle.

 

Yeah, a quart every 1,500 miles is great for an engine with over 100k.

I had a Buick with a 350 and 135k once that used a quart every time I filled the gas tank.

As for the coolant... Now I understand.
If you get an overflow bottle (a soda bottle with a hose in the top will work fine), and you have a "Vacuum / Pressure" radiator cap, AND there are no signifcant leaks in the system,it will suck the fluid back in when it cools.

- Eric

 

Yeah, I rigged an overflow bottle, and switched to a rad cap that had "return overflow" or something similar on it. We'll see what happens with THAT.

Compression test read 100-130 PSI, those two being the extremes.

 

I hope the new cap works out for you !!!

 

So do I! We'll see!

 

I would suggest removing all the plugs and pressurize the cooling system over night try to keep 15 psi on the system and in the morning are after a few hours have some one spin the eng. over while some watches at the spark plug openings to see if coolant comes out the plug holes, make sure u stand aside and not directly in front of the plug hole. as an auto tech we cked. head gasket leaks all the time this way and it would tell on what cyl. the leak was
thanks ray

 

Im with MD sounds like head gasket or head, if there is a crack in the head on the exhaust side it will just pump it out into the exhaust on the compression stroke and bypass the plugs altogether.
If the heater was leaking, inside the car would be muggy and the windows foggy but check the hoses anyway.
If the cars an auto check the trans isn't fuller than usual.
But a pressure test will confirm.

Scott

 

feel the carpet around the passenger front seat area. Coolant can leak out and not be obvious at first. Makes for an oily feeling wet carpet.

 

Gotcha on all counts. I'll do what I can before I button her up again this weekend.

EDIT: The radiator caps in question:

hlrazMd.jpg

 

http://www.ebay.com/itm/VINTAGE-AC-R...194993&vxp=mtr

Any auto service shop should be able to test a cap for free probably.

 

Can't tell you, how many bad caps I serviced when looking for coolant leaks, it's the first place to look, also sometimes the rad. neck, inside where the cap is supposed to seal. Pressure test everything before you take anything apart.

 

Seff, it's pretty busy at work today, so I can't get too deeply initi this, but the RC-15 that you had on your car originally is, according to my limited research, a pressure-only cap, while the other one looks like a pressure-vacuum cap.

The pressure-only cap let's pressure out, but not back in, while the pressure-vacuum cap allows the radiator to suck the coolant back in from the bottle.

Check the bottoms of the caps - the P-V cap will have an extra central flapper button that can move downward, allowing it to suck fluid in.

- Eric

 

I've run out of time for now, but the overflow and the 'new' cap are in place. We'll see if that makes a difference.

 

If you want the coolant to return to the radiator from your new overflow resevoir, there's two other things you should do in addition to using the proper type of suction cap:

1/ Make sure the hose extends all the way to the bottom of your overflow resevoir. Otherwise you'll be suckin' air.

2/ Fill the radiator all the way to the top, and even fill your resevoir about 1/3 full. That way, if you ever see the resevoir is empty, you'll know the radiator has sucked extra coolant back in, meaning you really are losing it somewhere. Your system will constantly be pushing coolant into the resevoir and sucking it back in. That's normal.

In contrast, with the older style, one-way caps, you never want to fill the radiator all the way. You need to leave air space so the coolant can expand without overflowing.

 

Roger on all the above. I'll get that done once the car is cold.

Thanks.