Bleeding a PRRT-equipped cooling system- Solved!

[k80rum]

Has anyone that's fitted one of these have a technique for bleeding the air out of them?

 

I appreciate that being a mod, there isn't exactly a 'standard installation' for it, but if anyone's got any tips I'd be interested to hear them.

 

To date I've refilled the system 3 times - one being last night and twice I've had an airlock that's proved very difficult to shift. I'm not sure how I managed to avoid it the last time but I did.

 

I have my PRT mounted horizontally above the steering rack. Twice when I've experienced an airlock on filling they've occured at the same place - just in front of the PRT, at the exit of the rad. The symptoms are that the bottom radiator hose stays cold and judging by hose temperatures the stat doesn't appear to open.

 

I'm pretty sure what's happening is the following: The thermostat is shut when I fill the system, coolant fills the bypass and enters the rad at the top. As the water filters through the radiator, it's trapping air which is forced out of the bottom, into the S pipe the bottom of which connects to the rad outlet and the top of which connects to the PRT a few inches higher. The air is then trapped against the stat which is shut because its cold.

 

I'm filling the car as I always have - with the front jacked up and the expansion tank held high, hitting and squeezing hoses to dislodge any air bubbles. When coolant come out of the rad bleed screw at the top, I replace the bleed screw, make sure I've got some coolant in the expansion tank and run the engine up to temperature. However the airlock is still in the radiator bottom hose and because it doesn't heat up, the stat never opens and therefore the radiator isn't used.

 

Any suggestions? The only other things i can think of doing are loosening off the rad hose clip on the PRT to try and make sure air is purged at this point.

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54

 

Edited by - k80rum on 9 May 2008 11:08:46

 

Edited by - k80rum on 14 May 2008 13:36:14

[henry21p]

I put a little hole in the stat... Allows air/warm water to bleed past

[k80rum]

Thanks Dave - a top idea. I think I might give that a go.

 

What sort of size hole are we talking; 3mm or so? I take it this was on a remote thermostat as opposed to an OEM one in the housing next to the block?

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54

 

 

[7 wonders of the world]

Never had a problem with mine mounted in the same place:

 

It is possible to get air in the J hose if this runs higher than the OE stat housing however providing you have a bleed screw on the radiator header as the water trickles in the rad will fill and even if there is a little air trapped in the S hose once the stat opens which it will as there nothing to stop the warm water flowing in and out of the other 2 PRT unions this air pocket will circulate back into the engine and be bled by the 6mm hose to the expansion bottle adjacent to No 1 inlet. - check this line isnt blocked too!

 

Is your PRT outlet positioned slightly upward? as this will enxourage natural bleeding of the system.

 

 

 

Too young to be old !

[7 wonders of the world]

Just thought are you running a CC DS system? in which case the PRT is held some 100mm higher than normal making it higher than the OE stat housing as the S hose is 100mm taller.

 

Too young to be old !

[henry21p]

given that coolant is slightly more "viscous" in appearance than water (at room temp), want a hole big enough that little bubbles can actually get past etc... 3mm was what i did. just make sure when you install it that it's at the top, not the bottom, so air comes out in the right direction.

[Bricol]

Did you take the original stat out? Or rather, that the middle bit out of the orginal stat and re-insert the newly created washer back into the housing and re-install? You don't want the original stat in there, but I do think you want some restriction in there - hence re-fitting the washer.

 

My PRRT stat is installed so the hose back up to the rad top hose is uppermost. I have throttle bodies with no restriction in the hose to the expansion tank and a bleed tee in the top heater hose - although I'm not now convinced one is needed with the PRRT system.

 

I simply refilled it through the expansion tank. Left the level in the tank up to the top of the neck, cracked the bleed on the top of the rad, and the bleed tee cap, re-tightening each one as coolant came out, checked the level, fitted the expansion tank cap and then held it at 5000rpm for about 1.5 hours on the way to Stoneleigh. No air lock and temp nailed to 82 C on the guage. No jacking, no squeezing.

 

And it was similar on first installation a couple of years or more ago.

 

Bri

[k80rum]

Thanks 7WotW.

 

Perhaps I've occasionally been unlucky or have been filling the system too quickly - In my case it seems that the air bubble sitting against the thermostat on the inlet/radiator site prevents the thermostat from opening at all. As I understand it, the water temperature on this side is what will cause it to open and it's not as the hot water isn't able to reach it due to the air. As you say, air anywhere else can circulate and vent via the 6mm manifold tapping.

 

Interesting I've never been aware of air trapped in the J hose on my car, although it can collect there during filling. Being the silicone type makes it easy to squeeze and this is enough to displace any that accumulates. The main advantage here though is that it is in the 'vented' part of the system so it has somewhere to go.

 

Because I don't run a heater and haven't taken the water rail off the head to seal the old bypass outlet, I run a 15mm bypass hose from the water rail around to a T piece, which connects to the other end of the traditional bypass on the block-mounted (now empty) thermostat housing and to the expansion tank. This 'bypass' arrangement is a bit un-necessary, but it seems easier than trying to cap the ends.

 

Edited to add: Good thought about the longer S hose I'm running a Pace system though, so the S hose is the same - definitely slightly lower than the OE housing - if anything, my J hose has a very slight upwards run to it. Thanks though!

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54

 

 

 

Edited by - k80rum on 9 May 2008 11:25:40

[k80rum]

Dave21P: Okey-doke. cheers for that

 

Bri: Yep, I removed my old thermostat and replaced it with the spacer ring and washer I was using a bleed tee in the heater hose but have now done away with it because like you, I'm not convinced it achieved anything with my setup - air trapped anywhere else can be shifted with a bit of squeezing or seems to vent naturally when the engine is run up.

 

Your filling method sounds almost exactly like mine. Maybe I could try filling it slower and letting a bit more come out of the radiator bleed screw. I probably don't need the front of the car jacked up to fill it either. I definitely think I'll give Dave's hole a go though, I think with the layout of the system now, it's an easy point to trap air which wouldn't escape unless/until the thermostat opens.

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54

 

 

[henry21p]

too big a hole and you get a problem with the system not working as intended as too much is bleeding past - meaning it takes AGES to open the thermostat...

[7 wonders of the world]

If your not running heater Id be inlcined to blank off the water rail outlet and the inlet to the OE stat housing thus forcing all the water via the PRT otherwise your bypassing the bypass so to speak - which will slow down reaction times at the stat.

 

I run Pace DS to so I use the short S hose which SFS now make in silicone !, veiwd from the front my PRT outlet is about 10 o clock so air naturally bleeds from this, with the PRT itself stat about 5mm obve the rack.

 

Too young to be old !

[k80rum]

Thanks both.

 

One small hole now drilled and cleaned. I'll see how I go.

 

For those that have blanked off the heater bypass, how have you achieved this? I've tried silicone blanking caps without much success, a bolt plugging a piece of hose (which shot out on the drive after a run I could just try tightening the jubilee clip further but it didn't seem like a great solution in any case)

 

What did the K racers do? I connect the expansion tank to the inlet at the housing so that end's not an issue, but were there ever K water-rails without the bypass outlet in them (I must say, I've never seen such a thing), or is it just a case of taking the rail off and getting a plug/cap brazed in? If there's a choice, I'd rather get one that doesn't have this outlet in the first place..

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54

 

 

 

Edited by - k80rum on 9 May 2008 12:18:45

[Nifty]

Darren,

 

I'm slightly confused with your argument because it is the bypass water temperature which causes the PRRT to open, so any air block on the radiator side of the thermostat would not affect opening function. Arguably, if the thermostst has to open against an air block rather than water then the opening should be slightly easier due to the compressability of the air

 

I'm running with a heater and a CC Gold dry sump.

My PRRT is mounted vertically where the S pipe would normally be (i.e. I butchered an old standard S pipe to cut out the vertical section.

Although I was originally going to make my own bypass union pipe that would allow the heater return to feed back into the system before the PRRT, a need to get the car back on track meant that I have retained the original return/bypass to the thermostat housing. Also the R400 engine had neither a thermostat in the housing nor a restricting washer .. I have put it back on the engine as it came off.

 

The result of all of this was that the engine sits at a rock steady 82^oC even when the oil temperture is getting quite high on track.

The radiator fans will kick in at the correct temperature when left standing to heat up and the water temperature gets up to temperature, opening the thermostat a lot quicker than the previously.

 

 

Some poor pictures of my set up can be seen here.

 

 

Forgot to say that I bled mine in exactly the same way I did pre-PRRT, jack the front as high as possible so the radiator bleed is the highest point.

When Jason does it he drives the front axle onto the 4 poster and then lifts the car up about 3 feet, never had a problem yet

(Famous last words .. I'm hoping to get it out of hibernation this afternoon .. watch this space ❗ 😳)

 

 

 

Keep off the straight and narrow 😬

 

Edited by - Nifty on 10 May 2008 09:52:46

[Bricol]

Well that's the general position of mine - but mine is orientated slightly differently. The bypass back up to the top hose is vertical on mine. The connection to the slightly shorter "sub" pipe is angled back.

 

I left the restriction in the stat housing, I seem to recall, to ensure the heater circuit did something . . . I think . . . maybe. Which it does.

 

And as I mentioned, all I do is fill the system, let air out of the rad and heater hose and put the cap on. It's just done a blast to the Model Engineering show at Harrogate, a crawl through a red hot Harrogate, and a good blast on a different route home - nailed to 82 C.

 

PRRT system opens under pressure too tho I think, as well as temp.

 

Bri

[Nifty]

Part of the reason for mine being quite as it is is because i have air horns mounted above the steering rack.

 

Keep off the straight and narrow 😬

[k80rum]

Thanks chaps.

 

Nifty, you raised a good point about the PRT bypass temperature causing the thermostat to open. I'd thought it was the PRT inlet (or radiator outlet in hose terms).

 

Given this, and that the PRT relies on pressure, perhaps pressure is the underlying cause of my stat not appearing to open now, rather than there being an airlock (which I think is unlikely in the PRT bypass hose).

 

Perhaps the PRT bypass, combined with an obstruction-free heater bypass is lowering the pressure enough to affect operation.

 

I've only recently fitted the bypass hose and although I'm not 100% sure, I *think* I used a heater bypass the first time I had thermostat-opening problems. I think the time it's worked well has been when I've tried my capping attempts. Perhaps in your cases, the fact that the heater is present helps to keep the pressure high enough that the stat works as intended. My heater bypass is effectively increasing the diameter of the PRT bypass hose and lowering the pressure in it. Does that sound plausible?

 

 

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54

 

 

 

Edited by - k80rum on 10 May 2008 17:23:51

[Nifty]

Darren,

 

This web page gives a good description of how the PRRT works and the flow through it at various temperatures/openings

 

 

(P.S. I lied about my air horns .. they are actually below the steering rack )

 

 

Keep off the straight and narrow 😬

 

Edited by - Nifty on 10 May 2008 18:12:49

[Nifty]

Darren,

 

I've just started mine up for the first time this year.

 

I watched the gauges carefully and was surprised to see that the water temp got almost to 90 on the gauge before suddenly falling down to 82^oC.

 

 

Keep off the straight and narrow 😬

[k80rum]

Cheers Nifty!

 

I've found a 16mm cnc milled plug that should let me block off my water rail nicely. Just waiting on that to arrive and I'll fill it up and see how it goes.

 

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54

 

 

[k80rum]

My CNC'd blanking plug arrived today and I've just refilled the system and returned from a blat, where the water temperature was nailed at 85 degrees throughout.

 

I filled the car while it was on the level, with the expansion tank raised and the radiator bleed screw out until it wept. Cap on, run up to temperature and voila.

 

I can only assume that if you use a PRRT it's worth blanking off the heater bypass unless you have a heater fitted, otherwise it seems the extra bypass decreases pressure enough to affect the operation of the PRRT.

 

Now to get some more blatting in if I can!

 

Darren E

 

K80RUM Website and Emerald maps library

 

Superlight R #54

 

 

 

Edited by - k80rum on 14 May 2008 13:43:07

[Peter Carmichael]

This web page gives a good description of how the PRRT works and the flow through it at various temperatures/openings

---

 

Interesting read. The description of the restrictive flow of the bypass circuit is exactly what my datalogging was showing up the other week(header tank cap failure datalogging)

[TorAtle]

I chopped off the excess part of the water rail and had it welded. The outlet on the plastic thermostat housing now goes to the expansion bottle, and the outlet on the connecting pipe has been transformed into a bleeding point .