Air-locking radiator
 

Those of you who were at Llandow will remember that I exited the first track session after about 4 laps in a satisfyingly spectacular cloud of steam, having airlocked my radiator and overheated. Various debates ensued about the placement of bleed points for the top of the head and since then I have fiddled on with it without reaching a satisfactory conclusion, and I still need to stop and bleed the radiator every 150 miles or so (or more frequently if I'm driving hard). Experimentation has shown there is no air trapped in the head and my bleed position purges this back to the bottle fine. What seems to happen is that the airspace in the expansion bottle migrates to the radiator during driving - i.e. the bottle ends up almost brim full and the air is in the radiator instead.

My expansion bottle is set up to feed into the radiator return hose next to the thermostat, and bleed back from the head outlet casting. All I can assume is happening is that turbulence in the expansion bottle entrains bubbles down into the coolant which then only settle out in the radiator. Anyone else suffered similar problems? My thoughts were to baffle the expansion tank (with a sponge block perhaps), restrict the bleed line to a smaller size (it's about 6mm at the mo), or fit a permanent bleed back from the radiator top to the expansion bottle at high level down the side of the chassis.

Any thoughts?
Richard

Richard

Sounds an intersting one, for fear of the silly question, is the expansion tank as high as it can be? The other thought is, would a non return valve be of any use, the baffles ideas was my imediate reaction.

Be intersted to hear others thoughts.

Steve

Hi Steve,
For info, yes, the tank is in the "standard" marlin position on the main bulkhead top tube and as high as it could be without fouling the body. It is certainly the highest point in the system.
Where in the system did you wonder about the non-return valve? I've been wondering if one of the central heating type "auto-bleed" valves on top of the radiator might do the trick, but then I also need a way of getting air back in to the expansion bottle...

Richard

My initial thougts were to put it in the top return pipe, my idea would be, if the water cant flow back via the small pipe, then nor can the air. This maynot be the best conclusion, but for me it would be my stater for 10. The other thing is, is the seal on the expansion tank cap good, on the rover they reccomend it to be changed every couple of years, it maybe alowing air though under pressure. Beyond that, I am at a loss.

Steve

Rich,

If you're considering trying a different expansion tank I'd suggest a VW globe style tank, as they're very cheap from the likes of GSF and ECP. The VW tank is certainly baffled in some way.

I did also wonder about an auto-air-valve, but I would think it'd be better to cure the cause, rather than deal with the effect.

Cheers,

John.

Rich, been away so only just read your post!

I found it interesting as it brought back a memory about a conversation I had with a honda elise converter ages ago.

I dont know the why and the hows just relaying what was said!

Basically I asked the question why is it that someone would spend £10,000 upto £19,000 on a honda conversion (yes that is how much they cost) but they keep the crappy expansion tank from the k-series?????

The answer was that the expansion tanks are all brand new from rover and not the old ones but the reason it is the rover tank is that plumbed correctly they found it was the only tank that did not suffer from air locks in the system??????????????????

Strange?? yes very but any honda conversion on any elise anywhere will be plumbed exactly the same with the rover tank no matter who carried out the conversion.

The tanks dont even look as high as ours are either

http://i157.photobucket.com/albums/t...hurricane2.jpg

http://i157.photobucket.com/albums/t...version322.jpg

As I have said I don't know and you are the only one of us with the car on the road so I don't know how mine will behave yet just thought I would share this with you

Just thought I'd bump this back up the forum as John was asking if I'd had any success. Short answer is no! Regular radiator bleeding still required. However, I'm now looking at the problem again and finding out some interesting stuff. First I've finally noticed that when the engine is cold, instead of purging coolant back into the bottle, the bleed pipe gently sucks in air from the bottle (not sure what makes it do this sometimes and not others.... maybe heater control position or just thermostat position).
I was prompted to look at elises by the pics Craig posted above (which I'd missed seeing first time round Craig, sorry!). Doing a bit of digging I turned up this useful site:
http://www.elisetyper.com/archives/25#more-25
If you look about a third of the way down you notice that the expansion tank has a one way valve in the bleed inlet.... Aha! It looks like Steve was on to something. Digging further it seems (at least some?) Rovers might have this feature in their bleeds:
http://forums.mg-rover.org/archive/i.../t-148671.html

So - I'm going to see if I still have one knocking around in my Rover bits, or else maybe even better I was thinking of installing a dip pipe from the bleed inlet into the tank going to the bottom, so any suck-back takes in coolant, not air!

I also noticed the elise conversion makes use of the vacuum control position on the outlet casting to take off the bleed. Is this what you have used, Craig and John? I have my coolant temp sensor there right now but I was thinking of adding a Tee and connecting both the sensor and bleed to this point.

Anyway, I'll make some changes and report back.
Richard

Rich,

Yes, I have, and to my knowledge so has Craig, removed the wax-stat air bypass from the head coolant outlet. I only see water going into the header, not out, though when cold and at idle the flow is negligible.

My retest is on Monday, so I'll watch the fluid level on mine again, and see if it remains where it is - certainly no air made its way to the top of the radiator last time. After seeing your car, the bleed valve on the rad inlet pipe was one of the first things I checked when I got to the SVA.

Cheers,

John.

Rich, mine has never been driven any distance but has idled for a couple of hours non stop and never had any issues with the way it is plumbed (the same as the honda elise)
I have not installed the one way valve yet as I was told that I would not need it plumbed the way it is but hey I'll wait and see, I did remove the gobin on the top and replace with this
http://i157.photobucket.com/albums/t...y/DSC00153.jpg

As for the coolant sensor I put mine here as it's very neat! Only took five minutes to tap into the blanking plug above the oil filter

http://i157.photobucket.com/albums/t...y/DSC01078.jpg

Ta for the replies. I've gone ahead and installed a small-bore dip-pipe into the tank now. Been idling for a while up to full temperature with no problems (but then it always seemed to idle fine and only really drew air through when I was driving. Weather forecast for tomorow is nice so I think a test-drive is in order!
Where did you get the quick-release fuel fitting Craig? I looked everywhere for those damn things and eventually fitted a compression fitting instead (the rail being a handy 8mm).

Good luck with the retest John. Looks like Monday is going to be a great day for a drive :)

Richard

Rich, the quick release was already on the engine all the hoses etc were still attached but you can buy them from honda or eliseparts I think sell them in shiny alloy
Craig

Craig is that your engine in the top picture??

If so, that is seriously clean! Did it ever see service in a car, or was the car binned within spitting distance of the dealership's forecourt????

As you know, my engine, after the last drive, looks like someone sprayed it in road turd! It was clean, prior to the drive, though the cam cover had missing paint (battery acid removed it during the donor's crash).

http://www.johndry.com/enginebay/200...ne_bay_004.jpg

http://www.johndry.com/enginebay/200...ne_bay_005.jpg
http://www.johndry.com/enginebay/200...ne_bay_006.jpg

John, no it's not mine haha mines actually cleaner than that engine and has braided hoses I will post an identical pic when I take one and see what you think!

The elises have undertrays and the sides are sealed so tend to stay really clean my car has 19k on the clock

I thought I recognised that image, from when you paid a visit to the garage that converts Elises to Honda power.

Rich - weather was glorious here today. I know you live somewhere north of the M4, which is a different world to the tropical south, but I presume you managed to brave the elements and give the header tank a test.

Problem solved?

Yay, problem solved, yes!
My little dip pipe mod seems to have done the trick. Spent much of today hammering round North Wales and not a sniff of air has made it to the radiator. Weather was cloudy with some sun but great driving conditions.

You know it's amazing how friendly people are when you have an interesting car - coming over to chat and so on. I was getting petrol this afternoon (this is required quite often) and the whole crew form the tyre place came over for a look. The boss, who knew his stuff was talking to me about the suspension because I mentioned I was trying out more rear toe in, so he offered a free tracking check once I'd filled up :) I'm now running 3mm toe-in at the rear and it's amazing how much more planted it feels. I have also got the diffuser fitted now which might make a bit of difference too I suppose, but I'm inclined to think it's mostly the geometry!
Richard

Excellent - an easy fix too!

Yep, I know what you mean about onlookers, and that's from my very limited exposure - I had an unusually long chat with the garage attendant when I filled up a few weeks ago, and this evening a number of yoooofs walked past while I was putting the car on the trailer, and all of them, including the girlies, said in unison "cool car".

That said, driving through Crewkerne on the way back from the SVA, some old fella took exception to the noise (I was driving at a constant 32 in 5th), looked at me with displeasure, and waved his walking stick. I look forward to being an old git, when I can pointlessly moan about the young-uns!

Richard

Pleased you are all fixed up now, always a feeling of elation when a problem is resolved, and now any more of the guys can benefit from your experience as always with this forum.

In the matter of on lookers I have had the quite abit and even after a number of times its nice to talk about the car and the build. I had a chat with a guy yesterday as I picket the good lady up from work at lunchtime, it was so nice here it was an open top day.

Steve

Just a quick note on this thread!

I have done 1k now with no one way valve and no air locking issues so guess it was down to the way it is plumbed??

Craig