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best way i know geoff, is to have the car on a flat surface & remove the bottom radiator hose from the radiator, have your heater switch right over on the "hot" side, that opens the heater valve & lets most of the water out of the heating system..........i think using the radiator hose to drain has the same effect as "milking" a car of petrol, the force of the water escaping the larger outlet creates a "suction" effect.............just my thoughts

Yes, it's a bugga to drain. There is a drain plug in the block on the exhaust side but I couldn't get at it. My technique was:

1. Drain the system at the radiator drain plug. Re-fit drain plug finger tight.
2. Re-fill with tap water, leave the radiator cap off and start the engine.
3. Loosen the radiator drain plug so that coolant starts to trickle out slowly. Adjust the trickle rate after proceeding to step 4.
4. Keep topping up the radiator so that the water stays just below the filler neck.
5. Let it run until only clear water comes out of the drain.
6. Close drain plug, fill radiator, wait until the top hose is warm and switch off.
7. Drain radiator again.
8. Fill with coolant concentrate and de-mineralised water as required.

Question JBT.
Doesn't this method end up retaining more \"tap\" water than before?

With the low cost of demineralised water, wouldn't it be better to introduce/sacrifice that to the system when purging the coolant rather than filling up with tap water?

Jules

Also, with the JBT method, does the thermostat stay open even when your flushing the system with cold water?

Is there an easy way to keep the thermostat open so you can flush the block as well or can you remove it all together for the purposes of a flush?

Sirbob,

I would REPLACE the thermostat whenever changing the coolant.


Jules

jules wrote:Doesn't this method end up retaining more "tap" water than before?

Nope, because it's pretty much (85%) all emptied out again. But you could use de-mineralised if you want. The coolant concentrate should neutralise any gooblies in what little tap water is in there.

sirbob wrote:does the thermostat stay open even when your flushing the system with cold water?

Yep, because the added water mixes with the hot water so it stays hot enough to keep the thermostat open. The idea is to set up a trickle flow out of the radiator drain and that way it won't just dump all the hot coolant.

jules wrote:I would REPLACE the thermostat whenever changing the coolant.

Overkill Jules. Every 6 years or at timing belt/water pump change would be enough.....if you've been changing the coolant every two years.

So you reckon 85% of fluids are expelled when you remove the bottom hose and/or open the radiator tap?


Jules

Yep, rounded up to the nearest 5%. I got 5 litres out of the 6 available.

OK, cool.
I'm going to do mine when I do the timing belt. I had to do a \"claytons\" anyway on the weekend when I took the condensor out, but I just used coolant and demineralised water (no flush yet).

Therefor I think I'll do the following.

1. Remove bottom hose.
2. Remove the thermostat and temporarily replace the housing.
3. Reverse flush radiator with tap water.
3. Flush the engine through thermostat housing.
4. Replace thermostat and hoses
5. Fill with coolant concentrate and de-mineralised water as required.

It's just another option that may be easier if you are going to replace the thermostat. Mine hasn't been looked at for 3 years, so it's going to go.


Jules

What you plan to do Jules is ideal, especially as you will have the thermostat out anyay. Are you getting all new hoses too?

My method is just the \"disturb nothing\" way of doing it between cam belt changes.

To be honest JBT, I hadn't even considered the hoses
I guess the bottom one is actually getting pretty soft, at least it felt pretty soft.

Perhaps I should add them to the list (which is getting very long). All the small hoses have been replaced.

Jules

Just to clarify, turning on the heater in an MX-5 won't change coolant flow, so you're not going to trap any in the heatercore by having the heater off. Thermostats will typically last a long time, also.

There's a bolt covering a coolant feed on the side of the block which was designed for the turbocharger on the original 323 that the engine was taken from. If you remove this you'll get even more coolant out, as when you drain the coolant from a cold engine, there is still coolant trapped in the block between the water pump and thermostat.

JBt's method would be easier, though.

Where on the block, and is it very accessible?

Jules

The plug





More here

I've always parked my car slightly up hill when doing coolant changes in fear of retaining air pockets in the head when refilling. If you've owned a VL you'll know what I mean.

Easiest way to drain is to rip the hoses off and start her up for 20 seconds, if the car is cold this is fine to do. I did my MX a while back, pretty straight forward job.