Radiator Caps

[phil Dean]

Its me again. I had the car tuned yesterday and the tuner said it was running lean at the top end before he tuned it. The car gets a bit warm and he thought the tune might help to cure it but he pointed out that he thought the rad cap wasn't the correct one. I have noticed it feels a bit loose before when I have topped it up. When you unscrew the cap with a cold engine am I right in thinking 1 turn anti clockwise  and the cap should  pop up. You have to put a small amount of pressure on it and turn anti clockwise again to then get it off My rad cap has no resistance you just turn it once and then turn it again. I have measured the underside of the cap to the rubber seal at the base 21 mm the neck of the rad is 20.7mm. its stamped with lbs 7 on it.

Could this be what's causing the slight over heating gauge going up to 3/4 hot using the heater in the car and then the electric fan to bring it down to nearer normal.  I have to say you can,t move in this town without hitting traffic. Between my house and the car tuners in the next town 4 sets of road works so that doesn't help.

 

Phil.

[Z320]

Hi Phil,

there are shorter and longer rad caps, you need the longer one to get a preload on its gasket when you lock it.

I use a 13 PSI cap, 7 PSI should also work.

Don’t believe those telling you all air has to be out, don’t overfill the rad, let enough air in there to be compressed by the expanding coolant.

Ciao, Marco 

[RobH]

As Marco says - It sounds as though you have an incorrect short 3/4" cap  and need the 1" type GRC101.  When you put the cap on it should drop down until the sealing washer hits the flange. You then have to push it down against the spring and turn it clockwise about 1/4 turn to secure it. 

This won't affect the heating in traffic which sounds completely normal to me, but having 7 lb pressure will raise the boiling point of the coolant. 

[RogerH]

Hi Phil,

 have you got the expansion bottle that catches water from the pipe running fron the Rad cap neck.

This allows water out of and  back into the Rad when things get a little toasty.

Without this  bottle and the correc rad cap you will lose some coolant.

See items 76, 72 & 71    HERE

Roger

[Z320]

With enough air in the rad (no problem for the waterpump) I drive my TR4A with a always try overflow bottle.

This prevents sucking coolant back which had time to catch frech oxygen (opend cooling system).

I know all others tell you different, feel free to decide how you want.

Ciao, Marco 

[RAHTR4]

Hi Phil,

The information below is as printed on the box of a period AC radiator cap.

Regards, Richard

 

[Z320]

Lovely sticker!

[keith1948]

Hi Phil

On my 4A the rad cap is rated 7psi. As Rob says above you should have to push the cap down against the spring and turn 1/4 turn to secure it. I have the expansion bottle mentioned by Roger.

I also have a plastic multi blade fan as fitted to TR250 instead of the 4 blade metal fan and no problems with overheating.

Regarding overheating - possible things to check - 

Is the temp gauge sender giving correct reading? - from what you have said I think that is ok.

Is thermostat working correctly - possibly from what you have said.

When was last time you flushed out the cooling system and filled with fresh coolant/antifreeze.

Keith

[phil Dean]

I spoke to TRGB who I bought the car of they said some caps don't have much spring in them it is a 1" cap, I have a bottle expansion tank, the radiator was flushed along with the block just before I bought the car. I asked at the show on saturday about fitting a TR6 fan on a 4a more blades etc people seam to think it wasn't possible to do. When I got back yesterday I checked the engine block with a digi temp gauge. Block at the back 80 degrees at the front 78 degrees. reading on the temp gauge about 3/4 from cold. 

[RobH]

80ºC is about normal as a running temperature - my TR3A normally runs just under an indicated 185ºF = 82ºC which is half way on the dial. 

[keith1948]

Hi Phil

As I said I have the TR5/250 8 blade yellow fan on my 4A. It has been on the car for over 33 years. Just have to make sure there is enough clearance to rad because blades flex with use. Part number 308353. It just bolts on using the 4 holes in the fan extension. The TR6 one which has more blades might not fit. I have driven in France in temperatures close to 40C with no overheating issues.

Fitting an uprated water pump might help by pumping water through rad more efficiently. A slipping fan belt would reduce efficiency.

Advance/retard can alter engine temperature. Can't remember which way round but sure someone here can advise.

There are 3 different thermostats for hot/normal/cold climates but they simply open or close sooner or later but don't affect engine temp once it is warmed up.

Keith

[RobH]

1 minute ago, keith1948 said:

There are 3 different thermostats ......... but don't affect engine temp once it is warmed up.

Yes they do Keith. The cooling system has to have  excess capacity to allow for hot days so is capable of over-cooling the engine - engines can run too cool if the thermostat is stuck open.  The thermostat throttles the water flow to prevent that when the engine isn't working hard. 

 

[RobH]

1 hour ago, phil Dean said:

I spoke to TRGB who I bought the car of they said some caps don't have much spring in them

That sounds dubious.

It's the spring that sets the pressure in the rad. The diameter of the throat is about an inch so say 0.78 square inches. At 7psi that is 5.46lb so for the cap to work it must surely take some amount of force to compress the spring when you fit it.  If there isn't any preload it won't seal. 

I just tried mine and there is that sort of resistance over the last 1/8" or so of travel.  

Edited August 17, 2023 by RobH

[keith1948]

2 hours ago, RobH said:

Yes they do Keith. The cooling system has to have  excess capacity to allow for hot days so is capable of over-cooling the engine - engines can run too cool if the thermostat is stuck open.  The thermostat throttles the water flow to prevent that when the engine isn't working hard. 

 

Hi Rob

Yes I would have agreed with you until I read this article which stated that a colder thermostat will not solve overheating problems. Still not sure they are right though.

https://help.summitracing.com/app/answers/detail/a_id/5284/~/should-i-run-a-colder-thermostat%3F#:~:text=If you want your engine,will NOT solve overheating problems.

However if the thermostat is not opening correctly or fully then the engine will run hotter. So thermostat might not be fully opening. I have a box of old thermostats that should all open at 82C but instead open at a range of temperatures. I put them in water in an old saucepan and heated it up on a hotplate and measured the temperature of the water. Some open lower and some open higher than 82C. 

Keith

[RobH]

No they are right - a cooler thermostat won't compensate for an inadequate cooling system, but a properly designed and working cooling system has surplus capacity and that is what the thermostat regulates continuously to try to keep the water near the thermostat opening temperature. 

[keith1948]

5 minutes ago, RobH said:

No they are right - a cooler thermostat won't compensate for an inadequate cooling system, but a properly designed and working cooling system has surplus capacity and that is what the thermostat regulates continuously to try to keep the water near the thermostat opening temperature. 

So the question now (coming back to Phil's plight) - is what exactly is wrong with his car. Could it be thermostat not opening as it should. He has measured the engine temperature as about 78 - 80C which seems about right. Does that mean his temp gauge is reading high? That could mean the sender part number GTR104 may be faulty or maybe the voltage stabiliser ( for negative earth) giving high readings on temp gauge? According to Moss catalogue page 101 issue 18 a high temperature reading could be caused by a faulty voltage stabiliser. Modern versions of these are polarity sensitive so it's important to get the right one. The older type with a bimetal strip inside were not polarity sensitive

Here is useful info on voltage stabilisers

https://mossmotors.com/media/instructions/131-555.pdf

Keith

[RobH]

It seems to me the gauge is reading high - it may well be the voltage regulator but that would make the fuel gauge read high too of course.

Edited August 17, 2023 by RobH

[rcreweread]

4 hours ago, keith1948 said:

Hi Phil

As I said I have the TR5/250 8 blade yellow fan on my 4A. It has been on the car for over 33 years. Just have to make sure there is enough clearance to rad because blades flex with use. Part number 308353. It just bolts on using the 4 holes in the fan extension. The TR6 one which has more blades might not fit. I have driven in France in temperatures close to 40C with no overheating issues.

Fitting an uprated water pump might help by pumping water through rad more efficiently. A slipping fan belt would reduce efficiency.

Advance/retard can alter engine temperature. Can't remember which way round but sure someone here can advise.

There are 3 different thermostats for hot/normal/cold climates but they simply open or close sooner or later but don't affect engine temp once it is warmed up.

Keith

Keith - I have a feeling Marco or one of his dutch colleagues did some tests in the past to see how much more efficient the uprated pumps were, and if I remember correctly, they were found to me no more efficient and potentially less efficient than a standard pump!

Phil - should you find you need any parts, I have reconditioned OE Radiators, pumps, bellows thermostats and temperature gauges - I haven't got spare rad caps, sender units or voltage stabilisers

Cheers Rich

[Z320]

Finally there is not much you can or must improve on a TR4/4A cooling system.

I don’t own a TR6 or earlier 2/3, but it seem to be the same to me.

If you have a cooling problem on your TR you have to solve it and not fit any „uprated“ parts.

A different thermostats, what ever temperature, you gain nothing. Because with the engine hot - all are fully open the same way of travel.

With my experiments I became convinced a summer thermostat makes no sense and is only hope.

Ciao, Marco 

Edited August 18, 2023 by Z320

[John Mellor]

I have little knowledge compared to you guys but my experience driving through Spain in temp at times greater than 35C was that the gauge barely moved  beyond 185F even in heavy traffic. This is a bog standard TR4 ( rebuilt by Neil Revington over several years ) with metal fan blades. So surely in UK ANY increase in temp means problem somewhere in cooling system or temp recording/sending.

I have learned that filling coolant right up into the "neck" is pointless due to overflow and a barely visible coolant level is safe and sustainable and I've stopped looking for the leak I always thought I had

Sorry if this is a simplistic view

Regards

 

 

[Z320]

1 hour ago, John Mellor said:

I have learned that filling coolant right up into the "neck" is pointless due to overflow and a barely visible coolant level is safe and sustainable and I've stopped looking for the leak I always thought I had

Sorry if this is a simplistic view

Regards

 

 

Good point;

all TR2-4 don't have a overflow bottle, and with enought air in the system this works without loosing coolant.

The overflow bottle came (with the hole story of "fill in 1/, blow out and suck in") with the TR4A and I'm convinced this a  "bottle of desperation".

Because the factory and traders had no other possibility to get rid of the ongoing complaints from customers,

which are not getting tired to overfill the rad and complain about "loosing coolant".

I've been told from TR6 owners their TR6 work lovely with empty overflow bottle and without any cooling problems.

Ciao, Marco

   

[phil Dean]

Heck opened a can of worms here. Ref the voltage stabilizer been there done that got the t shirt I had a similar problem on my Avenger that was voltage stabilizer related both the temp gauge and fuel gauge used to show high, changed the stabilizer 2 or 3 times problem was that my dash was a smiths one most early Avengers were AC Delco and V stabilizers were plentiful for the Delco dash and dials but not for the smiths one's  In the end I had a voltage stabilizer built for me dropping it down from 11 volts to 9 volts still the same problem never did totally solve the problem before I sold the car. I do not think the petrol gauge is reading high, I have noticed the car is fitted with a newish voltage stabilizer although it could still be a problem. Maybe I should go back to basics. Take the thermostat out  A pan of boiling water first and see at what temp its opening. New rad caps are not that expensive I might just buy one and see how that goes. I intend to take it out for a decent drive on Monday I have owned the car for nearly 3 months now and all I have done is drive around locally and mostly work on it to improve it. So we shall see if it is better on a longer run on country roads not just moving from 1 set of roads works to another. Which has been the case around here lately.

Medium term the next big job is to change from dynamo to alternator and listening to various people at show last week this could be a good time to go for the narrow fan belt conversion which means radiator out although TRGB said they had flushed the rad   and the block out I might have the rad checked out. There's a good company round the otherside of Manchester  have used before I might try them again. 

I am just wondering if I have made the situation worse by fitting an electric fan in front of the rad, it does block some of the natural flow of air thru the rad. I use it sparingly because running a dynamo you switch it on and under 2000 revs the Ammeter goes left negative charge very quickly.  Maybe rethink this take it of when the rad is out run without it for a week and see if the temp is still going up. 

Phil.

Edited August 18, 2023 by phil Dean

[RobH]

I use a blower fan but rarely have to turn it on - normally only needed if standing in traffic when there is no airflow anyway. 

[Jtex60easy]

I agree with Mr. Mellor’s statements. Two mornings ago I headed out through the north Texas prairie. It was 26 degrees Celsius. When I got back into my urban traffic light arena, it was a full 40 degrees as it has routinely been this season. Once up to operating temperature, my aftermarket gauge moves back and forth slowly between 185 and 195 as the thermostat controller switch turns the electric fan off and on as needed. Stopped in traffic or doing 70mph, the slightly larger aluminum radiator does not send any coolant past the 7lb. cap and into the overflow bottle I thought I needed when I was listening to car guys who drive something else. I have learned to just let the engine keep the coolant about half way up the height of the filler neck.

Phil, as far as new or special parts go, you have to go with whatever ambient conditions demand. If you are going with a future alternator, be sure all of your relevant wiring is ready for it. 
— James

[phil Dean]

Yes James I will start researching it in a couple of weeks before I do anything.