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Coolant Filling

Postby Stuart McGuigan » 06 Nov 2015 16:05

Anyone who has done the job will know what a pain it is to refill the RV8 cooling system when changing the coolant, or following work on the system. Filling has to be done very slowly and, in the final stages, you are as likely to fill the valley gasket as the cooling system, when trapped air coughs back through the filler pipe. No amount of squeezing of the top radiator hose will fully purge air locks from the system, and entrapped air will accumulate in the arch of the hose when the engine is running - leading to reduced coolant flow and possible engine overheating.

I have devised a solution in the form of a bleed insert fitted in the top radiator hose. The unit is shown below: [IMG_5098.JPG[/attachment]
A prototype fitted to my car is also shown below: [IMG_5098A.JPG[/attachment] My company has now made a small batch of the bleed inserts and these are now available through Clive Wheatley at V8 & RV8 Parts.

The procedure to fit the bleed insert and fill the cooling system is as follows:
1. Partially drain down the system so that the top hose is emptied. Cut the top hose in the centre of the arched portion. Fit the bleed insert, secure with two 45mm hose clips [preferably stainless steel] and remove the bleed screw.

2. Set the car heater control to 'hot' [in order to fill the heater matrix with coolant].

3. Remove the coolant filler plug located to the right of the inlet plenum chamber. [You will probably already have replaced the original unreliable plastic filler plug with a metal one. If not, standard flanged brass plugs are readily and cheaply available from plumbers merchants - or on EBay; the size is 1/2 BSP.]

4. Remove the expansion tank cap.

5. Fill with the correct type and strength of coolant via the filler pipe, until the correct level in the expansion tank is reached. [It is necessary to fill fairly slowly to avoid spillage from the filler pipe. A plastic funnel screwed into the pipe is helpful, as is wrapping a piece of absorbent rag or kitchen roll round the pipe to catch any spills.] There should be minimal coughing back into the funnel when pouring the coolant in, and self-purging of entrapped air in the system via the bleed screw hole as the system fills up.

8. Refit the expansion tank cap when the level is correct and then continue to fill until coolant starts to issue from the bleed screw hole in the bleed insert. A rag placed under the insert will catch any small spillage.

9. Refit the bleed screw, with its sealing washer, and tighten. Continue to fill until the fluid reaches the top of the filler pipe.

10. After a trial run - and after allowing the system to cool, of course - depressurise the system by removing the expansion tank cap and top up the tank to the correct level, if necessary. Replace the expansion tank cap. Then remove the filler plug, check the coolant level in the filler pipe and purge any remaining entrapped air by simply 'cracking' the bleed screw. Top up the filler pipe after purging and replace the plug.

11. You should also check on your trial run that the heater is actually working, which of course it should be, since the heater valve will still be open!

12. After a few more runs, it is wise to recheck for entrapped air, as at point 10 above.

The above twelve point procedure still appears fairly involved when written down step by step, but is quick and easy to carry out in practice and - as Clive Wheatley says - it works a treat!
Bleed Insert Fitted
RV8 Bleed Insert for Top Hose
Last edited by Stuart McGuigan on 12 Nov 2015 09:05, edited 2 times in total.
Stuart McGuigan
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Joined: 21 Aug 2015 18:37

Re: Coolant Filling

Postby V8webmaster » 06 Nov 2015 17:24

A very useful modification and part too. I will add the note to the RV8NOTES series.
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Re: Coolant Filling

Postby Peter Garton » 07 Nov 2015 07:42

Well done, a jolly good thread, Stuart, which is going to be a boon to RV8 owners since we have all been through the filling nightmare, so often!
Peter Garton
Posts: 43
Joined: 16 Dec 2012 16:28

Re: Coolant Filling

Postby Peter Varley » 11 Feb 2017 05:06

Hi Stuart,
I have just had one made up from your photos (see photo attached). However as you can see my local radiator repair shop went a little overboard. I am in two minds as to weather I will leave it or simplify it at a later date. Thanks for the idea. In case you are wondering as to why I did not purchase one of your designs, my one only cost $25AUS to make and that included the hose clamps. Freight to Australia would have been about the same about the $25AUD.

A little overkill
Peter Varley
Posts: 19
Joined: 19 Dec 2012 06:39

Re: Coolant Filling

Postby Philip Irving » 11 Feb 2017 08:36

Just a comment from my side: Over last few years of ownership, I have changed the coolant completely many times but I've never had an issue at all with re-filling the coolant system.

My secret is to use a plastic funnel (regular one from a hardware store) which can be screwed lightly into the header rail filler - this ensures that the coolant never spills on the engine or into the V, and allows you to vigourously squeeze the top coolant pipe to push out the air. The funnel may occasionally fill with coolant, but won't overfil.

I think it's self-explanatory but if someone would like a photo how it looks let me know.
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Posts: 31
Joined: 11 May 2013 19:00
Location: Cologne / Bonn, Germany

Re: Coolant Filling

Postby Peter Varley » 12 Feb 2017 00:08

Hi Phillip,
I hear what you are saying. I used the same procedure, but how do you really know that your system is totally free of trapped air ? The bleed screw also cuts down in the time to complete the job if refilling the system (see the RV8 Note 357 by Peter Garton who also uses your procedure and comments "is a job that can take several days").

Draining and refilling the RV8 coolant system
Following a query raised on the V8 Bulletin Board, Peter Garton sets out the procedure he uses to drain and refill the coolant system on his RV8.. (Apr 12)

It must be emphasize right from the start that refilling the coolant in a 3.9 litre V8 engine with an RV8 is a job that can take several days. The reason for this is the series of air locks encountered by the amateur. The airlocks result in no heating or a loss of water level visible in the expansion tank! Patience and still more patience is required here. Thus we can commence by draining off the coolant.
Peter Varley
Posts: 19
Joined: 19 Dec 2012 06:39

Re: Coolant Filling

Postby Philip Irving » 13 Feb 2017 12:14

For sure, like everyone else - I experienced that there is no way simple way to eliminate the trapped air on the first fill. I will usually top up once or twice after replacing my coolant until it stabilises and the air is out of the system.
I guess I don't find the refilling procedure I use too onerous.
Nothwithstanding this, this is a nice improvement suggestion !
Philip Irving
Posts: 31
Joined: 11 May 2013 19:00
Location: Cologne / Bonn, Germany

Re: Coolant Filling

Postby Paul Taylor » 13 Feb 2017 21:59

The bleed nipple in the top hose looks like a good idea. Would just add that, like Philip Irving, I use a plastic funnel - with an 'O' ring rolled onto the funnel neck which seals when pushed into the filler pipe. I then use a small (1 litre) jug for pouring and try to carefully deliver a thin, clean 'thread' of coolant into the engine without flooding the funnel and hopefully avoiding air pockets. Initial filling only seems to take 30-40 mins.
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Joined: 06 Jun 2016 21:41

Re: Coolant Filling

Postby Stuart McGuigan » 17 Feb 2017 18:11

I have now devised an improved top hose insert which, in addition to facilitating filling of the system, makes the top hose (and thus the whole cooling system) self-purging of entrapped air, once correctly filled with coolant. This is described in the attached file. My wife and I toured the Basque country of Southern France and Spain in the car last year and she proved entirely free of overheating - even when crawling for more than half an hour in a traffic queue, in ambient temperatures in the 30s.
RV8 Self-purging Hose Insert.doc
(1.23 MiB) Downloaded 62 times
Stuart McGuigan
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Re: Coolant Filling

Postby Martin Cridford » 17 Feb 2017 19:52

A great idea Stuart. I've been thinking along the lines of the MGF/TF arrangement which is similar.
Those that know the F/TF will know that cooling system has at least two few self bleed pipes, on the cooling system and the head, running back to the coolant expansion tank in a similar way to Stuart's scheme.
As the F/TF is mid-engine with long cooling pipes to the front mounted radiator in addition it also has 3 other system bleed points that must be bled several times before air pockets are cleared. One on the engine cooling rail, one on the heater matrix and one on the radiator itself.
In spite of their reputation for cooling problems a well maintained F/TF will not suffer overheating if the system is kept in good condition. A low coolant alarm is also recommended!
Martin Cridford
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Joined: 20 Feb 2016 08:19
Location: Exeter, UK 1995 RV8 1422, 2003 MGTF 160 Sprint

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