Haggisbash

I gave the car a WOT wind up through the gears and held it in top foot flat to get some readings on the O2 meter, I will post my query about that separately though. After this run when I got home I noticed some coolant had come out of the overflow tank and that this was full. Thinking that maybe I had overfilled the system I left it to cool and then looked in the radiator, the coolant was about 2 inches from the top and only about a pint had been sucked back into the radiator from the overflow tank. When I started out the rad was full and there was about a pint in the overflow tank which normally gains about 2 or three pints which then get sucked back into the radiator.
My concern is where is all of the air getting into the system from? There are no obvious leaks in the system and over time the radiator seems to gain air but this time very quickly!
There is no oil in the water or water in the oil but I'm starting to wonder if this engine is becoming a "kettle" and one of the heads might be cracked. The PO had a reconditioned set of 882 heads fitted to the engine (this was about 15 years ago) and I heard they are susceptible to cracking, could I have a combustion chamber crack pressurising the cooling system or maybe its a gasket issue? Suggestions anybody?
'70 coupe fitted with 74 SBC. Engine seems pretty standard, low HP probably std cam etc.

Kacyc3

Have the cap tested to make sure its good, check the lower hose for an internal spring to keep it from collapsing. A collapsing hose could cause the cooling capacity to change/be reduced while at WOT causing the cooling system to pressurize and blow past the cap into the bottle. A bad cap may be to weak to hold the pressure of the system and allow it to blow past or won't allow it to suck back into the radiator.

Haggisbash

Hi KacyC3 the rad cap is new and seems to work okay, in fact made no difference to the previous one so I have ruled that out as a cause. Good point about the lower hose though, although it looks good on the outside I have never looked inside it for a spring, I guess if I give it a decent squeeze and I can collapse it this might give me a clue

Haggisbash

Hi, Kacyc3 I checked the lower hose it appears to have a spring in it but not all the way through, at the top corner where the hose turns and connects to the water pump I can collapse the hose by squeezing it, should the spring continue around this bend in the hose?

MelWff

Does the new radiator cap have the necessary rubber seal around it's outer edge to permit the coolant to be sucked back into the radiator as everything cools off?

Haggisbash

Hi, yes it does.

mikem350

Make sure the overflow hose to the recovery bottle has no leaks and if needed add clamps to the ends. Also that the bottle can actually allow the fluid to flow back to the rad.

I have seen your problem before. Its got to be the overflow hose or the cap. The correct way to fill the system is fill the rad all the way when cold, and fill the bottle to the "cold" mark. When the fluid expands, it will rise to the "full" on the bottle. This assumes that all air has been bled from the system.

REELAV8R

You could try something like one of these kits to see what you have.

http://www.autozone.com/loan-a-tools/block-tester

Usually once it gets bad enough you will be puking water out of the overflow if combustion gasses are pushing water into the overflow.

DUB

I assume your radiator cap is 15psi CLOSED SYSTEM cap.

All above suggestions a spot on.

You do not have to worry about the spring NOT being in the bend of the hose. It is unlikely it can get sucked shut there due to the bend in the hose and what it would take to do that.

As mentioned...the hose from the overflow reservoir to your radiator is CRITICAL. It MUST be a good hose and NOT leaking...or allowing air to get sucked back into your radiator.

Do not assume your radiator cap is good. Have it tested. I do not care if it is new or not.

Did the car run HOT when you found the coolant issue????

And if this engine is what you stated...A 1974 did not have an oxygen sensor to test or get values from.

DUB

flyeri

New does not mean it is working correctly. I've had a bad one out of the box. Could not figure out why it was dripping coolant (no reservoir) from the overflow tube on every drive. New cap, no more drips.

wzschirnt

Hi,

A 'home-grown' check for compression leakage into the water system -

On a cool engine:
- Take off the belt that turns the water pump.
- Drain some of the water out of the system. Half way down in the radiator will work.
- Remove the thermostat housing and thermostat.
- Fill the block through the thermostat hole until it is full.
- Have a helper start the engine and watch the water level as you slightly rev the engine.
- If water level moves at all or bubbles show up, there is a leak somewhere.
- DON'T do this for more than a minute, as the motor will start to build heat and the level will come up because of that. The problem will show up almost immediately.

- Put back together and contemplate your next move. Perhaps to the fridge for a beer??

Good luck.
walt z.

SH-60B

Lots easier to just buy the kit that detects combustion gasses in the coolant. Advance auto has them. If it's real bad you can smell it in the overflow tank.

DUB

I use my coolant system pressure tester and hook it up to the radiator and crank the engine. If there is a blown head gasket..the pressure will begin to climb instantly.

DUB

carriljc

Hope I didn't miss something here, but I'd try swapping to another radiator cap before anything else. It might just be a bad radiator cap....

texas jim

Great post and great info. Thanks much. This site is still great!

Haggisbash

Hi DUB, I have tried 3 caps with the same result only this last run was the worst.(was also the first time I've buried the gas pedal in the carpet for some time).
The hose to the overflow bottle is new and not leaking.
The car did not run hot, once warmed up it typically sits at 170 - 190 degs at this time of year here.
I had a bung welded onto the exhaust so that I can use My Innovate Motorsports A/F ratio gauge on this engine.
I checked the level of the radiator, the coolant level is 2" below the cap, the balance of the coolant (4 Pints) is in the overflow bottle.
Question: does the overflow bottle have to be higher than the radiator cap? It is not at present.
Once I get the carb reinstalled I'm thinking of drilling a hole in an old radiator cap and soldering a nipple onto it so that I can attach a long piece of plastic hose to it which I can point somewhere safe as the engine warms up to see if I can purge all of the air from the system. The angle of the radiator means that not possible to fill the radiator completely. I guess the other option is to have a sealed rad with a pressurised overflow tank and have the pressure cap on it.
FWIW When I got the car it had nothing but an overflow pipe that dumped excess coolant on the ground, I'm not keen on that idea.
Last time I tried to run the engine with the cap off all was well and then suddenly there was a big burp of air that pushed coolant out of the rad which of course was picked up by the fan and sprayed around the engine compartment and on me leaving me with a mess to clean up.

tektrans

Maybe you just never got all the air out of the system to begin with.
I know on my car I have to put the nose up on ramps to get all the air to bleed out.

Kacyc3

That is a good question, I am betting we want gravity working in our favor and running coolant back into radiator when the valve opens. The water pump can push the coolant "uphill" when hot.

Haggisbash

Stupidly I figured that the pressure when the engine was running would have pushed the air out into the overflow bottle. I believe you are correct and I will have to do the same.

tektrans

Coolant has to fill the space before it can displace air-if you have air pockets, those will expand when heated and displace coolant (as you found out Lol) That's also why overheating coolant causes damage-the coolant boils and turns into a gaseous state which "displaces" the liquid coolant from that area (which now has nothing to cool it in that spot) and damage occurs.
The radiator fill cap is lower than the thermostat housing on our cars so unless you are filling at the intake there will always be air in the system. Get that nose up enough so the fill cap is higher than the thermostat housing and that will get rid of any air pockets-I really don't think it's anything serious at all.
Let us know if it worked out for you.