[35benzman]

hello,

I've gone through a number of cooling problems with my 350 chevy. Originally I had the radiator replaced; next I found that both heads were cracked and so replaced them; next I installed a high performance water pump plus a 25% solution of water wetter/distilled water in the radiator. Also replaced a couple of hoses and a 180' thermostat.

The overheating seems much improved and the engine does not appear to be loosing coolant. I have 2 temp gauges plugged into the intake manifold as I am now quite paranoid about overheating.

There are 2 remaining temp concerns: 1.) when the engine gets hot, coolant flows from the radiator into the coolant bottle - but when the engine cools down, it does not flow back to the radiator. 2.) the water temp runs under 200' when cruising down the highway but it will rise to 210' or more when chugging up a hill and in traffic a little more.

I replaced the radiator cap but that did not help with problem 1. The hose to the overflow bottle seems ok but I have not yet replaced it.

A fellow at a car show said I shouldn't worry about the coolant flowing back to the bottle - that's interesting - maybe true?

What are your thoughts about the overflow bottle? What about the temperature approaching 220' in traffic?

[alittle1]

When you remove the rad cap when it is cool before start up, what is the level of the coolant? ..an inch below the filler is acceptable.

The cap that is on the rad, is it for a closed system? A closed system cap usually does not have any turning lugs on it. and you must line the arrow up with the overflow tube to make it work right.

[35benzman]

The coolant level is about at the top of the radiator fins when cool, a little below the chamber opening. If I siphon the overflow tank to the level it was before the drive, and put it back in the radiator, then the level is just below the cap chamber (same as it was before the drive).

This is a closed system. The radiator cap is designed to seal at the top and at the bottom of the cap chamber. Within the chamber, there is an opening which connects through a tube to the overflow bottle. The cap has 2 valves, one to open at 13 lb pressure to release coolant to the overflow bottle, the other to open when the engine cools and creates a vacuum to suck the coolant back into the radiator. Mine is not doing the sucking back.

[oldbogie]

Originally Posted by 35benzman

The coolant level is about at the top of the radiator fins when cool, a little below the chamber opening. If I siphon the overflow tank to the level it was before the drive, and put it back in the radiator, then the level is just below the cap chamber (same as it was before the drive).

This is a closed system. The radiator cap is designed to seal at the top and at the bottom of the cap chamber. Within the chamber, there is an opening which connects through a tube to the overflow bottle. The cap has 2 valves, one to open at 13 lb pressure to release coolant to the overflow bottle, the other to open when the engine cools and creates a vacuum to suck the coolant back into the radiator. Mine is not doing the sucking back.

If yours is not pulling the coolant back there are 3 possibilities.

1) The cap return valve does not open as the system cools. A test would be if you open it when cooled off there should be a rush of air past the cap when its released enough to relax the force on the gasket.

2) The return hose collapses when the cooling radiator places a suction on it.

3) There is a leak in the system that would rather draw air than coolant as it cools off.

Bogie

[LATECH]

the top or bottom radiator hose could also be collapsing, be sure the anti collapse springs are in them, or they will collapse and not pull coolant back into the engine.

[35benzman]

The cap is new and the return valve seems to operate ok when I suck on it. I put my ear next to the cap and loosened it after the engine cooled some; I did not detect any vacuum sound.

I did replace the radiator hose - but I don't know anything about anti collapse springs - are these part of the hose?

I will try replacing the hose between the radiator cap area and overflow bottle.

But I do suspect there is a leak in the system - but where? And how to find it? I would think if there was a leak, shouldn't I see coolant discharge when the pressure is up? I don't see any puddleing and I don't seem to be loosing any coolant.

I'm thinking maybe a subtle leak that occurs only when the engine cools - could the intake manifold be the culprit? I have an edelbrock manifold and maybe I need to reseat it with new gaskets?

Any thoughts on how hot a 76 chevy 350 (with a few goodies to boost the HP) should get - is 220 ok when idling in the driveway after a drive?

[user151]

A long shot and may not apply, but the tube to the overflow bottle must go to (or almost to) the bottom of the bottle. And the end of that tube must be cut at an angle so that when it tries to suck back it is not attaching to the bottom of the bottle, that is, so it can actually suck water back in....

[denunger]

I'd bet it is your overflow hose/setup. The small hose breaksdown a little with age and collapses. But the big thihng is the clamps. You need good old fashioned steel worm gear clamps. They need tightening with age and weather. Some of these newer spring clamps seem ok, but any plastic notched clamps will not seal good enough. If there is even a little air leak, the radiator cannot refill from the overflow bottle. Every time you warm up your engine, you lose a little coolant.

[oldbogie]

Originally Posted by denunger

I'd bet it is your overflow hose/setup. The small hose breaksdown a little with age and collapses. But the big thihng is the clamps. You need good old fashioned steel worm gear clamps. They need tightening with age and weather. Some of these newer spring clamps seem ok, but any plastic notched clamps will not seal good enough. If there is even a little air leak, the radiator cannot refill from the overflow bottle. Every time you warm up your engine, you lose a little coolant.

A sufficient system, that being radiator capacity in BTUs of heat exchange and the fans in moving air through the core at idle, should maintain the operating temp around 10 to 15 degrees above the thermostat's opening temp indefinitely.

By the way, the overflow tank's cap needs to vent to atmosphere, something else for you to check. The lower hose is given to collapse from the suction of the pump, it needs to be stiff enough to resist that. Universal hoses have a spring molded in the corrugations. Direct fit hoses may or may not depending on manufacturer and how stiff they make their hose. The return hose does not have such reinforcement since it sees pressure so in operation doesn't collapse. However, in cooling down a vacuum forming in the cooling system could collapse it.

Bogie

[alittle1]

Originally Posted by 35benzman

Any thoughts on how hot a 76 chevy 350 (with a few goodies to boost the HP) should get - is 220 ok when idling in the driveway after a drive?

The temperature gauges in most cars today is only relative, as good as the money you spent on buying it. The true test would be using a mechanical temperature gauge, placed 1/4 to 1/2" into the stream or flow of coolant exiting the engine. And, the second part of the test would be the placement of a mechanical gauge in the stream of the inlet to the engine AFTER cooling has taken place. The difference is then the temperature differential which should be between 15 - 20 degrees at run position.

A temp. of 220 in the driveway with a ambient temperature of surrounding air of 70 - 80 deg, would seem to be reasonable if you were using a 13 -15# pressure cap.

You should be using a high temp vacuum hose with a spring clamp from the rad to the coolant overflow jug. The jug does have a small orfice in the top that vents to the atmosphere which allows coolant to rise and fall when warranted.

[4 Jaw Chuck]

This article from Chevy High Performance Magazine should answer your question, basically a downflow rad vents to atmosphere when its drawing back...the oveflow is just that...a catch can.

Crossflow rads work on a different principle as the cap is on the low pressure side, the article explains everything.

Pressure-Type Radiator Cap
Pressure-type radiator caps serve a purpose beyond just keeping the water in the radiator. On late-model cars, the pressure-type radiator cap is often found on the coolant reservoir instead of the radiator. If the cooling system were left open to the atmosphere, the temperature of the water would never rise above 212 degrees because it would boil out of the radiator and turn into steam. But because a radiator cap maintains pressure in the system, the boiling point is raised and the system is capped off. So the system pressure and the addition of antifreeze (containing ethylene glycol) raises the boiling point; while in cold temps below 32 degrees, the antifreeze lowers the freezing point (depending on the blend and capacity of the system).

Most of today's pressure-type radiator caps contain relief and vacuum valves. The relief valve allows the pressure (positive) in the cooling system to bleed out if it rises above a preset value, such as 16 lbs. When the engine heats up and the temperature rises, the excessive pressure pushes open the relief valve and blows off through the overflow hose. As the engine cools down, the vacuum valve in the cap serves to permit air into the radiator by opening when the internal pressure falls below atmospheric pressure (negative) after the engine is shut off.

Crossflow vs. Downflow Radiators
Crossflow radiators have radiator rows located horizontally so that water travels across the radiator, and downflow radiators have rows positioned vertically so that water travels downward. A crossflow radiator is typically more efficient than a downflow for the simple reason that the pressure cap is located on the low-pressure side (opposite the outlet or upper hose location). This cap location allows sustained high-rpm operation without forcing fluid past the cap. In addition, under-hood-space considerations typically allow a shorter and wider crossflow radiator to utilize a larger core with added surface area, which provides more effective and efficient cooling.



Read more: http://www.chevyhiperformance.com/te...#ixzz1YTbcYgHn