rise in coolant level

Thanks for the heads up, Nigel. The 160 still has its original head gasket, as far as I know, the elastomer one… The 135 had its head gasket changed a few years ago to something purportedly designed by an Aston Martin mechanic.

Richard

I thought I'd update this older thread with some newer findings.

As it turned out, after a drive the coolant level of my 160 still rose frighteningly from the max level at the seam of the expansion tank, almost to the rim, percolating as an old coffee pot. On a drive from The Hague on the A12 we got stuck in the Traffic Jam from the Apocalypse. Temperature on the coolant gauge rose to just above the halfway indicator, but then, still stuck in traffic dropped to the level I was used to in the 160 (slightly higher than my 135). Without me having heard the fans come on, rad nor engine bay. When I opened the boot lid at home, the expansion tank was wet on the outside. As it turned out after cool-down, I hadn't lost much coolant.

I decided to bleed the cooling system again for good measure. I unclipped the soft top, got the isolation out, removed the "bonnet", filled the expansion tank, slid a drip tray under the car, and started bleeding: radiator first, heater next, then coolant rail. I let the coolant gush out before redoing the bolts. Not a single air bubble in sight. I removed the hose leading from the jiggle valve to the expansion tank at the T-piece, shoved in an unused caulking gun nozzle and blew into the hose to see if the jiggle valve was stuck. Which it wasn't. I refitted the hose, started the engine and let it idle for almost half an hour. I let it cool down a little and restarted the bleeding process – this time without testing the jiggle valve. Again, no air bubbles. I screwed on a new expansion tank cap , and have made several trips since.

The coolant level rises somewhat, but not nearly as much as it used to do. No percolating. No visible loss of coolant. The needle of the temp gauge sits rock steady at the level of my 135, so somewhat lower than what I was used to in the 160, even in warm weather and dense traffic. I now tentatively permit myself to conclude the issue is resolved. But what was it that did the resolving? The second bleed? Did I unstuck the plastic ball from the jiggle valve? Is it the new cap?

As an aside: before I started the above procedure I tested whether the fans behind the radiator and the one in the engine bay were working, so I removed the plug from the sensor with ignition on and engine off (only engine bay) and with the engine idling (engine bay and radiator fans).

Richard

Thank you for checking back. All too often members solicit information & once their problem is resolve, nothing more is heard until another irritant hove into view & back they come. It you fail to respond to a feedback request on eBay you are hounded until you comment. Now there’s a thought.
M

But what was it that did the resolving? The second bleed? Did I unstuck the plastic ball from the jiggle valve? Is it the new cap?

Probably the new cap...

Hi. I hope it is ok to bump a relatively recent thread, to see if there are any further updates? I came across this forum as I appear to have a very similar problem. I recently had the head gasket replaced TF 135 for the first time, by a mobile mechanic. I've had car since new. The first few drives were ok. Then suddenly I noticed the coolant almost at the top of the expansion tank. The following day It was still high but I opened the radiator bleed screw and just as coolant eventually started to ooze out, I closed it. The level in the expansion tank was then back to normal.I bought a new coolant cap (from DMGRS) but if anything it seems to be worse. i.e. it happens more quickly. I wonder if my original cap was just starting to fail and keep sufficient pressure and the new cap was just DOA. If the consensus is that it is highly likely to be the cap, I'll order a new one, either from the same place or If I can find one in stock, elsewhere. Thanks.

The new cap failure rate is surprisingly high. There are cheap fakes out there and it is good policy to buy only from recommended suppliers. If possible pressure test any new cap. I only use original type caps and always carry a good spare. 

I have tried other pattern caps and they usually fail in short order.

Thanks for the good advice, David.
Who is your supplier of choice for your caps?

Rimmer Bros; Brown & Gammons; Mgfntfbitz

Ta

At least a couple of those places were/are out of stock but there are some available. I got hold of a second replacement cap and it appears to have fixed it. I'll do a longer drive tomorrow to make sure. The latest one was in a sealed MG Rover bag, unlike the DMGRS one which was just in a resealable bag. They are all identical except the latest working one has three letters printed on it, TRE I think from memory or something like that. No idea what that meant!

I got the same problem here and the the extensive bleeding 3 time with no air escaping .
Now i read here somthing thats calles a jiggle valve ??
where is that thing located and how do check the working of this ?

Just got back from my longer 2nd drive. All good. It's fixed!