Head Gasket Question

[GICarey]

Hi Folks,

Decided a new thread might be sensible for this question, rather than losing it within my overheating saga http://www.igmaynard.co.uk/bongo/forum/ ... 41&start=0.


So, cutting a long story short:

• Initial overheat led to replacement thermostat, radiator, and water pump, and what I'm told was a proper bleed according to the fact-sheet, via a local (now untrusted) garage.
• Snif-test (using the blue chemical which turns yellow) performed on the header tank doesn't identify any hydrocarbons in the water.
• Following above work, car drove fine for a 100 mile motorway journey at 2250rpm/60mph on Friday night, and five subsequent, short (2-10km) trips over the weekend.
• Upon first attempt at a reversal of the 100 mile motorway journey on sat night, overheat occurred within 3 miles. Nothing under the bonnet (i.e. hoses to/from rad; hoses to/from header tank) were warm, with cold coolant blowing out of the header tank overflow pipe.
• Dropping coolant, refilling, and following bleed procedure subsequently allowed a successful repeat of the 100 mile return journey home.

So, the questions then are:

• The type of overheat I'm seeing here appears, to me, to be zero circulation of coolant away from the engine, suggesting air block (else would expect rad top hose and header tank to be warming) - fair?
• Is it likely a Bongo will run for 100 miles fine, and then for some air in the system to have found its way to a bad spot in the system for a later journey? Seems odd/unlikely to me (would expect, once the stat is open, and water whizzing round, any remaining small bubbles ought to be sorting themselves out via the expansion tank?)
• Is it likely that bubbles are "getting in" somewhere when the Bongo is left to stand? Perhaps a pin-hole I've been unable to detect in a "bad place" is allowing air to be sucked into the system when the car stands for some time, whilst coolant loss remains insignificant/invisible from the header-tank? I shall have to get some of the UV chemicals a-la-Hayden to check for this.
• Can a head-gasket failure be such that everything will be fine for such a long journey, with air air subsequently being allowed between burn side and water when the engine cools? I've been of the opinion this is more of a "once it's gone, it's gone" thing, and more likely to be obvious with a nice hot engine than a cold one?
• Anything else which might be the cause? I'm still hoping it was continued poor-bleeding by local garage which was the trigger for all of this?

Thanks, again, for your time, and expertise!

Gav.

[Doone]

As the wife of a mechanic, personally I don't know enough about overheating issues to comment for sure on the technical aspects of your overheating problems. I don't know if the problems you are experiencing are due to air still being in the system because it hasn't been bled correctly, or because of other problems related (or not related) to the overheating episodes. From what you've written here, I would guess that there could have still been air in the system, or the thermostat jammed. Or there's a small leak letting air into the system - you can get the system pressurised to check for this. Fingers crossed the head is OK.

I can speak from personal experience of the Freda we own. It had overheated prior to us purchasing it. My husbands vast experience of overheated bongos led us to believe that as it had overheated a few weeks before we bought it, related problems may occur.

And unfortunately they did...

Hubby has written up what happened (on his website, on the 'Bongo Spec' page), if you want all the details. But in a nutshell, what happened was that it had previously overheated and the old owner had a new hose fitted, so we assume it overheated due to coolant loss.

When we got it, my husband noticed that the water pump was leaking, so he replaced it. As the 'standard' temperature gauge was just a little high he suspected there may be problems with the head, but the system pressure tested OK. The radiator was partially blocked so he replaced it and the thermostat and 4 main hoses.

It then ran for about 1,000 miles with the 'standard' temperature gauge needle happily at the 'normal' position. But the cooling fans were coming on a bit more often than they should. He wasn't happy with it and wanted to look at it again but was very busy so I just carried on driving it.

A couple of days later we were driving in heavy traffic at night and the coolant erupted through the expansion bottle. Anyone who has had this happen will know the noises and rumblings that accompany it are pretty dramatic.
It was not safe to stop where we were, so we had to drive a few hundred yards to a safe place to stop. Of course, my husband knew that the head was now wrecked.

He replaced the head etc and it's all running really really well now.

By the way, hubby is an expert bleeder of Bongos as Haydn (and many others) can tell you. So we were confident that our problems were not due to air in the system. We think that the initial overheating epsiode (before we bought it) was bad enough to weaken the head, which eventually gave up. Fortunately we bought the Freda cheaply with this in mind.

And so you're not demoralised, overheating problems can be due to someting as simple as a leak letting air in to the system which is simple enough to fix once you find the leak. I hope this helps and good luck with getting to the bottom of it.

[GICarey]

Thanks Doone, appreciate the commentary, am hoping ours was just a poor bleed and that our attempt was better (tho will have to be done again as there's no anti-freeze in there at the moment, difficult to obtain at 1800hrs on a sunday).

Oh, if only there was a good bongo garage nearby!

[Doone]

It's good to get these problems out there, so others know what can (but fingers crossed won't) happen. Fingers crossed too that yours is OK now, but if not no harm in checking for leaks - as you mentioned, the dye makes one easier to find.