Coolant flush ... today's tinkering exercise

[TR5tar]

I'm at it again. A couple of hours to spare, so I think to myself I'll have a crack at changing the coolant and testing the thermostat. Well, what else is there to do on a Bank Holiday? I know it would probably have been better to do it nearer the end of the year, but it's not been done in a while, so I wanted to get on with it and I'm bored anyway.

 

Right, bottom tap of radiator opened and coolant released. It's actually a nice blue colour and clean looking, so perhaps it's not necessary to do a flush. However, I read in the manual that as well as opening the radiator drain tap I should also open the block drain tap. Having looked around underneath I was unable to find anything that looked like the picture of it in the manual, but from the top of the engine I spot this this brass tap (see attached).

 

Questions: 1. Is that the drain tap? As coolant looks pretty clean, is it worth opening that tap and draining? Also, as coolant looks clean, is it worth using a chemical flush?

 

Cheers, Darren

Edited May 29, 2017 by TR5tar

[RogerH]

Hi Darren,

if it looks clean then I would put new antifreeze in and top up.

 

If you really wanted to do something extra you could remove the rad bottom hose and stick a hose in the top then bottom to move any large lumps.

 

Roger

[Fireman049]

Hi Darren ~

 

Puzzle find the drain hole in my 3A block!

 

With regards to opening your block drain tap. I would suggest that you fit some sort of drain

to prevent your starter motor being flooded. I changed my block drain tap to one with a lip

to which I fitted a length of plastic pipe.

 

Tom.

 

[Rob Salisbury]

Hi Darren, yes that's the block drain tap, if it's not moved for some time it may take some careful persuasion (they will sheer with not much force), you could unscrew the whole body from the block and tend to the tap on the bench, and at the same time have a bit of a scrape around inside the block with some stiff wire (coat hangers or welding rods are good for this) to dislodge any sediment and general crud.

Cheers Rob

[aardvark]

Hello Darren.

 

When I changed my nice looking blue coolant last year I drained the first bit into a plastic cup to check what sediments were in there and was surprised at how little there was floating around. Non the less, I opened the block drain plug and did the same. Still blue coolant coming out but clearly a bit of mud in there too. I resorted to a poke with a coat hanger and a lot of brown mud came out. I flushed the whole system frontwards and backwards and all good.

 

Summary, I'd always poke the engine drain hole even if the coolant looks clear.

 

Cheers

 

Dave

[TR5tar]

Thanks chaps.

 

Managed to get a bit of aluminium tube over the the bar and open the block drain tap. I let it drain out slowly so it didn't flood the starter motor too much, but that tap with a lip looks a good idea Tom. Where did you get it?

 

Water has finished draining from the block now and once again it was clear. No brown, rusty water coming through. I had bought some of that Forte coolant flush, suggested by Alec in an earlier thread, but with everything looking so good, I reckon I might save it for another time.

 

However, now just seen Dave's post. I'll give it a poke and see if I get anything!

[Fireman049]

Hi Darren ~

 

I can't recall where I got the tap from. I think it may have been Moss? I'll check my invoices

to see if I can find it. It may have come from my local Serk's depot?

 

Tom.

[TR5tar]

Poked it ... no crud, no more water coming through. Any point in flushing?

[aardvark]

by the sound of it, no point.

 

Don't forget to refill allowing the system to 'burp'.

[ianc]

Darren - with good quality modern antifreeze which is replaced every 2 or 3 years, you should not get any accumulation of rubbish by the block drain cock.

In the days when folk ran water in summer and anti-freeze in winter only, corrosion occurred and calcium deposits built up. Nowadays, it's usual (and advisable) to run anti-freeze (or waterless coolant) all year round.

From your description, I don't think you need to flush your engine.

Ian Cornish

[TR5tar]

Thanks Dave and Ian. I'll save the flush for another day.

 

By "burp" Dave, do you mean by squeezing the top radiator hose? Bleeding the system of air was going to be one of my next questions.

 

Also, one of the reasons I wanted to do the coolant change now was because I have a slightly odd issue with temperature. It's not the usual overheating, but rather that when I'm moving the gauge doesn't get above about a quarter. However, if I stop in traffic for a few seconds, the gauge moves quickly to the half way point and the fan kicks in. I've been wondering if the thermostat might be faulty, so I thought I'd test it. Now I have it out, I find it's a 74c one instead of the standard 82c. Would that account for the temperature not rising above a quarter when moving and if so would it be better to swap it for the 82c version?

Edited May 29, 2017 by TR5tar

[stillp]

Would that account for the temperature not rising above a quarter when moving and if so would it be better to swap it for the 82c version?

Yes, and yes.

 

Pete

[Guest ntc]

No and No it is fine as is,to burp the system have a mixture of water ready to top up,fill the rad cap off start the car and let it run the stat will open then top up bdq replace cap sorted,do not forget to have the heater valve open.

[TR5tar]

Hmmm, different answers on the thermostat.

 

If it's not the 74c thermostat that is stopping the temp going above a quarter when moving Neil, what do you reckon is causing that? I ask, because a few people have said that running the engine too cool isn't good for it. Of course, I don't want to make a change and then find I have overheating issues.

 

Thanks for directions on burping the system.

[Guest ntc]

Where it is, is how it should be as you have found out at halfway the fan kicks in, sounds like Robin set it right.

[TR5tar]

Fan does kick in at the correct point (half way), but when moving the temperature never reaches that point. It never gets above about a quarter. Only when I sit not moving with engine running for a few seconds, does the gauge move to half way and fan kicks in. But, yes, if it was Robin that put the 74c thermostat in, he must have had a reason for it. I'll drop him a PM to see what he reckons. Thanks Neil.

 

I guess the question is, is it better for the engine not to have it reach the higher temperature, or to have it running hotter and the fan kicking in more.

Edited May 29, 2017 by TR5tar

[Guest ntc]

Remember the sender if repro will not be on the money.Running it should be where it is at.

Edited May 29, 2017 by ntc

[Ben Freer]

As NTC suggests the gauge is not deadly accurate. They tend to be rather vague. The important thing is to notice when it changes from its habitual position. ????

[Nigel A]

My temp gauge used to read a quarter, changed the sender a while ago and now reads half

 

Cheers

 

Nigel

[TR5tar]

Yes, it could be a faulty sender or gauge giving an inaccurate reading, but we don't know that for sure. How would I test it?

 

To answer Ben's point, I do notice when the reading changes from it's usual position and it's very consistent. If I start the engine and idle it, the gauge will move to the half way point after 8-10 minutes (longer in cold weather), and once there the fan kicks in. When driving the car, the gauge never moves above a quarter, unless I'm stationary or moving very slowly in traffic, when it moves to halfway and again the fan kicks in. Therefore, the fan seems to be activating at the correct point (when the gauge reads just above halfway).

 

What we do know for sure is that there's a 74c thermostat in there. Would that not be an explanation in itself of why the temperature reading isn't getting above quarter when moving? What I'm interested to find out is if the 74c thermostat was fitted for a particular reason, perhaps to stop an overheating problem.

[Alec Pringle]

If you can put fingers on the top of the radiator for 2 seconds, it's not got past 1/4 on the gauge.

 

If you can't do more than touch the top for 1/2 second it's on normal running, I/2 way up the gauge.

 

If you get a blister, it's too damn hot . . . . .

 

I can't really see the point in investigating the cooling system and then doing only half a job - flush and backflush with the hose, then chemical flush, then both ways with the hose again. At least after that you know you're starting again from a reasonable reference point . . . . .

 

Cheers

 

Alec

[ChrisR-4A]

If the gauge is moving from 1/4 to half in some seconds then it sounds iffy. My 4a with only electric fan runs at lower mark of normal segment and then if stopped takes 1-2 minutes to move to just past centre of normal and fan comes on.

[ShaunC]

Should be an 82degC thermostat which is why the temp gauge was previously indicating low. Good find!

[ShaunC]

I guess the question is, is it better for the engine not to have it reach the higher temperature, or to have it running hotter and the fan kicking in more.

 

The target would be for the water temperature reading to remain constant at all driving conditions once engine up to 'normal' operating temperature.

 

In reality you should be able to get the system to run with a fairly consistent temperature gauge reading but it requires just a little fine tuning of the fan set point temperature, if adjustable on yours (which I would hope so). Also may depend on where your fan probe is? Mine is on the top of the radiator close to the top hose........always useful to measure the water temperature as close as possible to the fan probe with an independent unit when setting up and checking the dynamics of the system (on the run too) to see how close you are to the thermostat temperature.

 

Remember, the original engine driven fan would have been running all the time whilst the thermostat was modulating so you'll need your electric fan to come on before the thermostat has fully opened otherwise you'll get temperature overshoot which won't be a problem, but, like me you will want the temp reading as stable as possible like a modern car!

 

You may notice that the fan will come on more frequently but probably for a shorter duration, this should only be in slow moving traffic or when stationary though.

[Bill Bourne]

Hi Darren

 

I believe, there are 2 types of thermostat. 1 for summer running, i.e. the 72 and 1 for winter running - the 82.

 

Best Bill