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3000 MK1 BN7 overheating

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Norman

Norman

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Hi All - I'm new to this forum and new to Austin Healeys. I have just bought a 3000 MK1 BN7 generally in very good condition, but I have 2 issues to resolve. I have a gearbox issue (which I will post details of later) and a more urgent issue of overheating. If I drive the car sedately (40 mph) it is fine, but if I drive in a more spirited fashion (50 - 70 using the gears etc) the car throws a tantrum and ejects a lot of boiling water (about a quart) out of the radiator overflow pipe! The car mechanically is standard, and original although it has only done 41,000 miles - which probably means the radiator is also standard and original and 47 years old. The radiator cap has a 15psi rating (looks new) and the fan is original and belt driven. I am sure the issue of overheating is not new to this forum, so is it time for a rad rebuild, an electric fan (or both).
 
Hi Norman, Welcome to the forum. Perhaps the fan belt on the car is old and glazed or maladjusted causing it to slip at speed. Additionally the radiator can be all silted up and should be given a good cleaning. The 15 pound cap is not standard and should be replaced with a proper 7 Pound unit.--Cheers ---Keoke
 
Also, a radiator cap for a Healey (7lbs as Keoke pointed out) is a little deeper than most standard radiator caps. If you don't have the correct depth, the cap will not seal and the coolant will escape. Make sure you buy a correct replacement. Many of us have added overflow reservoirs. Generally these can be purchased at any auto parts store.
 
Also the fluid should not be filled to the top as with other cars. It seems to overflow until its happy then stops about an inch or so below the lower rim of the filler. What is the color of the fluid?
 
Hi Norman,
Welcome to the forum.
As Shorn & TH have mentioned, it's quite normal for the radiator to eject about a quart of coolant if it is filled cold & then warmed to operating temperature.

If the temperature is not actually going above 200F the usual solution is to not fill the radiator completely.

Many folks prefer to install a simple coolant recovery tank with a complementary top sealed radiator cap. As the coolant expands due to heat, it flows into the tank. As the engine cools, the coolant is drawn back into the radiator. This reduces the mess & assures that the radiator is full at all times.

As Keoke said, a 15 pound cap is likely to cause an unwanted leak. Look for a seven pound cap that has a one inch length from inside of top to the lower sealing surface. A genuine "old Brit" cap with top seal or the equivalent of the NAPA #703-1411 will work.

Also, as mentioned, a good cleaning & fan belt check would be advisable.
D
 
Norman -

The neck on 15 lb caps are shorter than the 7 lb cap, probably causing the overflow you are talking about because the cap is not sealing the radiator.

Get an original style 7 lb cap - should fix your problem.
 
Hi Guys - looks like that was the cure. I found that I live only 10 miles from SC parts (big in the UK for Healey and other marques) so I drove down and bought a 7lb radiator cap (long). Once fitted I gave the car a 15 mile run including some "spirited driving" and all is well, didn't boil once. I was however a little surprised at the gauge movement - seemed like quite a lot - don't ask for figures as the gauge is so close that I need my reading glasses to read it and I don't need any glasses to drive! It seemed to settle around the 180 mark and climb rapidly with some 3rd gear hard acceleration and cornering, then settled down with some steady speed cruising. Is this normal?

Anyway the good news is that it didn't boil. Once the weather settles down I will give the car a good 100 mile blast to see what happens. Thanks for your help.
 
Hello Norman, and welcome to the forum. I too own a BN7. Have you posted photo's yet?

When I restored mine I had the radiator boiled out and tested. I also added a CRS (coolant recovery system) that I made from pvc pipe, and fitted next to the radiator. Virtually unnoticeble when painted black. I generally run 180 degrees around town, on the highway it'll bump up to 190 degrees. The only leak I detected was from the spigot allowing coolant to the heater box. Replaced the wire clips with modern replacements, no leak.

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Norman -

I would suggest you have your engine block flushed and your radiator "rodded" at a radiator shop in the UK. you should also replace the thermostat while you are at it. It sounds "sticky" by your description.
 
OK, enjoying this forum thing - how do I post photos then.

Will change the thermostat on monday - what temp should it be?
 
Since you are in the UK 180F deg. should be fine for year around driving!
 
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