I have a 62 BT7 Tri Carb. The radiator was rebuilt about a year ago and two new rows added, it has a 165(or 160) thermostat installed, a flex fan(installed with the rebuilt radiator) and the engine lower end was rebuilt, new brass freeze plugs installed, etc. about 2 years ago. Since the radiator rebuild, the car does not get overly hot (233) except in extreme conditions (stop and go traffic @ 90) and even then the temp drops as it should when traffice clears, etc. I use 50-50 anti-freeze and have kept the coolant at about the same level adding when needed, since the rebuild.

About two weeks ago, I began to have major coolant loss problems only when I drive the car above 4000 - 4500 rpm (70 mph)or run up the revs in lower gears (I do not have overdrive). If I stay under 3500 rpm I do not lose any coolant. If driven at high rpm or speed the car will blow out the overflow tube a gallon or more of coolant. I have had the system checked (chemical and pressure) and I do not have a head gasket problem or cracked block. I assume the thermostat is working properly, because the engine temp reacts up and down as has been normal over the last two years.

The only potential villain that seems to be left is the water pump. Any other ideas????

I'd test or replace the cap before the waterpump; much easier and cheaper. It may not be able to handle the increased pressure.

For the conditions you describe, the w/p impellar would have to be quite eroded. Not that that couldn't happen...

My own car had been suffering cooling problems (no o/d on it either) but adding an engine driven fan (requiring me to remove my shock tower brace) seems to have cured that. At least for the time being...

I forgot to mention that I had replaced the cap. Cheap and easy is always the first choice for me. I have had the car for over three years and have not inspected or replaced the wp----no thought about it until now.

Hey ArtQ,

How much is 'major'?

The reason I ask is that my car also does quite well at low revs only loosing a small amount of coolant < half pint. At higher reves, cruising at 4,000 for example, it looses about one and a half pints, but it doesn't loose any more and it stays cool.

So I have put this loss down to the system needing expansion space in the header tank and the higher the revs and pressure, the more space it needs.

Is your loss more than one and a half pints?

Good luck

Maccers

This is a strange one. It's almost certain that air is being introduced into the system or the pressure cap is not holding. The most likely cause of air would be the water pump seals or combustion pressure leaking into the coolant.

A radiator shop can do a quick chemical test on the coolant to determine if combustion byproducts are present in the coolant. From your above statement, I assume this has been done.

Healeys require a longer pressure cap than standard, are you sure you have the correct cap?

Sorry, no good ideas.
D

Art,
If you used an after market thermostat instead of the original
skirted type of thermostat, it would be possible to install it upside down in the opening.
I think there would be a problem with the full flow of hot water like is needed under high RPMs if it were accidentally installed upside down.
In a low flow situation, enough coolant may pass through to keep it from boiling over as soon as the engine got to operating temp. Also, it is possible that the gasket is interfering with the full opening of the thermostat for some reason. If any formagasket was used to seal it up, a glob of it could be preventing the thermostat from opening all the way.
Since you have checked that there are no combustion byproducts in the coolant, I would suspect;
.. Upside down thermostat
.. gasket interfering with the full opening of the thermostat
.. bad water pump.
.. loose, slipping fan belt at high rpms.
.. a foreign object loose in the water passage of the head, at full flow, it moves up and blocks the water flow. When you let off, it returns to the bottom of the water passage and doesn't interfear anymore.
Good luck in your search for the gremlin,
Ed

Hi Art,
I used to have the same problem with my BJ8. I stopped topping off the radiator and the problem stopped. I have never flushed my system, stock old radiator and one of those terribly noisy stainless flex fans. I don't know what level one gallon short puts your fluid at but mine is 2 3/4" below the top rim of the filler and no problem on 100 deg. plus days.

Good luck,
Walter

HI Art,
First of all,What pound cap did you buy ? Second,Did you test the new cap with a pressure tester ? Seeing how a Healey has no recovery tank for expansion, the top tank will need an amount of space for the coolant to expand. Cooling systems seek their own level.As long as the coolant level always stays above the cores of the radiator ,you're ok. Losing a gallon of coolant is excessive.I'd be looking for pressure building up in this cooling system. Get the engine to operating temp. Without burning yourself,take off the rad cap and put on a pressure tester.Pump the tester to about 5 to 7 psi as starting pressure.Start the engine and watch the pressure gauge.If the pressure exceeds 16 psi I would think you do have a compression leak into the cooling system.If you have the tools to do this test , I think you should try it.Let me know the results.I will watch for your post. Good Luck.
Bobby R

After a successful chemical and pressure test, replacing the rad. cap with exactly the same type as had worked for two years and still having the problem, my next step will be to replace the water pump. The part is ordered and and will be installed on Monday. Also, since I live in southern CA and don't really need the function of a thermostat, I'm going to leave it out.

Thanks for all the ideas. Hopefully, the new water pump does the trick and I can get back on the road.

Everything I've read says you need a thermostat to restrict circulation so that the coolant stays in the radiator long enough to transfer heat. You should leave the thermostat in.

Agreed.

You also want the thermostat functioning so the engine reaches operating temperature as quickly as possible.

I don't completely agree. This is a commonly quoted misconception. Removing the thermostat can decrease cooling but NOT for the reason stated.

The rate of flow through the radiator cannot be too fast for the coolant to be able to give up it's heat. With more flow, the heat loss per pass through the radiator is reduced but offset by more water passing through, so the two balance out. Flow tests have actually shown that higher flow through the radiator can create turbulant flow in the radiator tubes which results in more "hot" water being in contact with the tube surfaces. Slower, laminar flow, results in the outer surface of the water column being cooled, but the inner part of the column never contacts the tubes. So turbulent flow can increase cooling.

The thermostat/restrictor raises the local pressures in the water jackets, especially around the exhaust valves, combustion chambers & reduces the tendency for localized hot spots to vaporize the coolant (spot flashing). With the restrictor, the localized (water jacket) pressures can be much higher than the actual pressure cap setting.

The second benefit is that by raising the head pressure on the pump, with the restrictor/thermostat, the pump inlet pressure is also raised (suction reduced) which helps prevent cavitation of the pump. Cavitation is basically when the pump creates so much suction that the fluid vaporizes in the pump internals, which reduces pumping capability.

Ref. "The Engine Cooling System" by "Technology Transfer Systems, Inc", Livonia, Michigan.
D

Had the same problem with a Healey years ago...it was the thermostat..cheap to pop in a new one..... had a "mechanic" put one upside down in my 62 Vettte years ago....sheesh!


Pete

An MGB in Louisiana will overheat when you remove the thermostat.

I stand by that statement.

I think you have a bad head gasket or cracked head, leaking combustion gases into the coolant.

This sort of leak cannot be detected by a simple pressure test because the combustion pressure is so much higher than the pressure you apply in a pressure test. But the combustion gases displace coolant and blow it out the overflow tube.

I have had this problem with modern cars, and your car's behavior is similiar my Subaru. This Subaru cooled perfectly until it was under strong load -- high RPM and high throttle settings, like climbing a hill at high speed. Then it would blow out coolant profusely. I did a lot of fruitless work on the cooling system before replacing the head gaskets -- that finally fixed it.

You can sniff the radiator gases for exhaust but at slow speed, you may not leak enough to be detectable. You need to sniff when the engine is under load, not easy to do.

Sorry for the bad news, but that's what I think is probably wrong with your car.

Good luck!

Bill S
Albuquerque.