Leaky AST Cap

[BenLewisMav]

I've had a search through some old threads and haven't quite found the direct answer to my problem(s);
1) Basically just that I noticed my alloy AST tank has leaked from the cap. I've seen it do it once just after I started the engine and it doesnt seem to have lost much coolant at all (both AST and filler neck levels are v.close to the top), but the area below the AST tank is very rusty, including all nuts and bolts below it, and the crossmember itself (to the point of paint flaking off). What is the knock on effect of the AST cap occasionally leaking?

2) It currently pretty standard setup (Type RZ), only the standard water temp gauge too (:(), which seems to go up normally from a cold start, but never quite reaches horizontal (9 o clock).. just sits somewhere shy of it (maybe 8 o clock), and when I was cruising (3000rpm/80mph) it seemed to drop a bit more, sometimes showing only slightly more than a quarter.. Is this realistic? What does a quarter translate to in terms of degrees C? My FC used to sit at around high 80's with a Koyo Rad.

[Nik da Greek]

I know there's loads of wisdom written about just how pointless the stock temp gauge is, but now I've got a proper GReddy one plumbed in, I can confirm that it's all true. My stock gauge, like yours, sits at nine o'clock, no matter what. Meanwhile, the GReddy one moves about loads depending on lots of factors, such as traffic, heavyness of right boot, speed, etc. I have a general range of between 80 degrees ish up to just shy of a hundred on really hot days in traffic, all the while the stock gauge doesn't budge a micron! Waste of space

As to the AST cap leaking, well, surely any loss of pressure from the cooling system will mean that the coolant can boil at a lower temperature than it's supposed to, since the pressure is what keeps the boiling point artificially high. This would obviously be, as Winnie the Pooh would say, A Bad Thing

[logicalChimp]

Hmmm

slightly off-topic, but Nik - did you add a greddy guage to the stock temp sender, or did you add an aftermarket sender as well? if you added the sender, did you try it wired up to the stock guage?

I'm just wondering where the prob lies - sender or guage, as I would like to get a 'useful' temp (and oil too) gauge, but keep the stock look...

[Nik da Greek]

No, it doesn't use the stock sensor. It's plumbed into the radiator hose using one of the cut and splice alloy unions with a tap for the sender already cut. Thus:
40573

I'm not sure whether it's the gauge or the sender that's cack on the stock set-up, tbh, but I certainly don't think I'd trust it any more, now I know better!

[nikp]

I'm not sure whether it's the gauge or the sender that's cack on the stock set-up, tbh, but I certainly don't think I'd trust it any more, now I know better!

If i recall correctly it's a bit of both. There are instructions somewhere on how to linearize the stock gauge so that it actually moves. But I can't remember where the instructions are!

If you have a power FC with commander, you can see engine temps already. I also used to have a rad temp gauge so that you could compare rad temps to engine temps - they can actually differ by a few degrees. Rad heats up first, and cools down first. Engine temps are usually more stable than rad temps.

[nikp]

Here we go: http://www.geocities.com/sdrx7_club/technical.html

[G@NDY]

Didnt notice that you had an alloy ast Bejamima . If its leaking I would suggest getting a good stock plastic ast, i had problems with 3 aftermarket types with the caps leaking. New Stock ast's are around £90 I think i recall so get a second hand one to try and save ££££

regards Andy

[G@NDY]

Heres one if you need it bro
http://cgi.ebay.co.uk/Mazda-RX7-Air-Separation-Tank-A-S-T-with-Cap_W0QQitemZ280260173559QQcmdZViewItem?hash=item2 80260173559&_trkparms=72%3A12%7C39%3A1%7C66%3A2%7C65%3A12%7C24 0%3A1318&_trksid=p3911.c0.m14

[antnicuk]

if its just the cap, get one from any motorfactors. Make sure its a 0.9 bar.

[BenLewisMav]

Cheers for the advice guys, will be buying that AST then. Tightened down the cap as much as poss and I haven't seen any more coolant leakage, but the whole subframe-y area below it is badly rusted so it must have been going on some time.. Better safe than sorry.

Great website too, tried fitting my Greddy warning meter water temp gauge to see if it was running hot at all, but the sender was fubar'ed, luckily had a spare sender from an oil temp gauge, unluckily when I tested it in boiling water from the kettle (95-100 deg) it read as just under 150 Deg C!
Also, when it was idling, just as the fans came on, it was right the way round off the gauge 160+.. Does this mean the fans come on past 100 deg? Or is the temp of the water actually reduced 'cause its pressurised?
Might need to see if I can wire in a resistor or something like that to make the temp match up. (Power FC on the cards however..)


Hope you had an easy journey back G@nd..
Pretty straightforward drive myself, popped by Hayward's as it was on route (just to have a peek around) but suprised to find them still there and just shutting up at 8pm!
Mental. Lots of nice FD's there, spoke to Carl about getting the car checked over and comp. tested next week.
Have you spoken anymore to Era about what way forward to go with the black beast?
Oh, and the guys a frickin legend! :) Really quality 'old boy' attitude, love it.

Tony, you *should* have mail!