When should rad cap release pressure?

Angus · Post by **Angus** » Thu Apr 11, 2013 7:48 pm

1. I burst a heater hose the other day ... on replacing, I notice a small smear of oil coming from the VTEC solenoid area, so that's my next job.

2. Over the last couple of years, I've had to keep an eye on my coolant, because the reservoir drains itself every couple of weeks. There's no sign of coolant leaks anywhere (believe me, I've looked). I've had a new radiator (about a month ago), silicon rad hoses and thermostat within that time. New water pump with timing belt only last week, though I am now running an underdrive crank pulley.

Today I thought I'd leave the overflow hose hanging over the front of the car to see if anything came out of it at any point.

Well, it didn't. This was after refilling and bleeding the system, taking the car for a 10 minute VTEC-engaging drive and then letting it sit at idle for at least 15 minutes - enough for the fans to come on twice.

Not one drop came out of the overflow. Meantime, the coolant hoses all got well pressurised.

I'd have expected some overflow by this stage.

I'm suspecting the radiator cap not releasing pressure - is that reasonable? Should it be spitting coolant into the reservoir by that time?

BTW, I never get any bubbling in the reservoir so I'm not thinking head gasket, and the car runs just fine.

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Thu Apr 11, 2013 8:27 pm

I don't think that's anything unusual at all.
The coolant level in the car should stay stable once it's all properly bled, provided there are no leaks/over-heating/over-pressuring etc. problems (i.e. everything normal and as it should be)

I actually gave up topping up the overflow tank a couple of years ago on the UKDM, 'cause it was just turning out to be a waste of coolant.
I'd top it up, it gradually evaporates and end up empty again.
The rad level doesn't drop, so there was nothing coming out of it to replace the evaporated stuff from the overflow tank.

Haven't driven the JDM/had it long enough to know how well that behaves, so I'm sort of topping it up (not religiously checking it, but if I'm in there, I'll probably have a look and maybe top it up).

Angus · Post by **Angus** » Thu Apr 11, 2013 9:13 pm

Wow - that's quite interesting. Can coolant evaporate out of the reservoir that quickly? There's not much room for it to escape - you'd think it would mostly condense back in. I need to add about a 1/2 litre every ten days or so to keep the level up.

The thing that made me think about it a bit more was the burst hose, which naturally led to suspicion of over-pressurising. But then the heater hoses are probably 20 years old, plus there's that wee dribble of oil from the VTEC solenoid area that must've got onto it (before the whole area was power-washed with coolant the other day!).

Today, after my run out and idle, the coolant hoses all felt pretty hard - which added to my suspicion of high pressure. So I let it cool and restarted the engine to see whether the hoses got hard quick (i.e. combustion gas, head gasket). They didn't - fortunately I've had a couple of GT4 Celica ST185s, so i know exactly how quickly rad hoses get with a leaky HG!

I might invest in a new rad cap anyway for peace of mind, seeing as the current one's several years old now.

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Thu Apr 11, 2013 10:11 pm

I hadn't really thought about it before now, tbh.

Maybe it depends how the car's driven?
If it's mostly around town driving, the engine bay will be hot and the reservoir's right next to the rad and near the exhaust manifold, so it will get quite a bit of heat soak.
If it's mainly used on long runs, it won't get as hot (a lot of cooling air over it, being right at the front)?

It's enclosed, but not really sealed. The fitting at the top is a loose fit in the cap so you can screw the cap on and as the rest of the bottle would be warm, it wouldn't allow the vapour to condense?

Dunno...

Post by **vanzep** » Thu Apr 11, 2013 11:29 pm

Ive had exactly the same on my BB4 - had to top up resevoir tank frequently- thought rad or hoses werent leaking but they were - first the upper rad hose balloned up but didnt burst, fixed that with a new hose, then i noticed the rad had a tiny hole in near the manifold and this was spraying onto the mani and evaporating hence no visible leak, so replaced the rad and coolant level in the expansion tank has remained constant ever since - i had trouble throughout in bleeding the system properly and eventually had to resort to the mouth over the rad filler neck and blowing the coolant through - that seem to clear the airlock and has not been an issue since - but now still paranoid about overheating when in stop start town traffic

im still assuming it might be a slightly lazy thermostat.....
hope this helps in some way

oh i replaced the rad cap as well

Angus · Post by **Angus** » Fri Apr 12, 2013 8:25 am

Well, I had a new radiator a few weeks ago (turns out the old one was pretty manky down the side of the fan shroud where I couldn't see it, thought that would solve the coolant loss, but it hasn't.) So I'll be a bit miffed if there's a pinhole in it. Will investigate, though.

Speaking of radiators, check this one that I took out of one of my Celicas (just after I'd bought it - I didn't let it get like that myself!

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Off to get a rad cap today, and see what happens over the next while.

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Fri Apr 12, 2013 11:49 am

Useful rad, that!

I took one out of a CX that wasn't much dissimilar. Couldn't see how bad it was 'cause from the front it was hidden by the air con condenser and the rear, by the twin fans. The only clue was the copper bits on the front of the engine!

My UKDM had a brand new rad fitted at Honda about 2 months before I bought it

Confused · Post by **Confused** » Fri Apr 12, 2013 11:59 am

A new rad cap is the cheapest to try first.

OK, actually, checking that the pipe from the rad cap to the expansion bottle is clear is the cheapest to try first. After that it's a rad cap.

You can then see whether the expansion/contraction of coolant is taking place correctly.

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Fri Apr 12, 2013 1:30 pm

This con-current thread relevant.

http://www.ludegeneration.co.uk/post114977.html#p114977

Angus · Post by **Angus** » Fri Apr 12, 2013 8:03 pm

Confused ... yeah, overflow hose is clear.

Went out this morning to turn the engine with the rad cap off. Huge gush of coolant from the rad. Bleh. Not a high pressure fountain, just a major dumping of coolant.

Filled up and "bled", tried again, more gushing. Switched off, attempted to bleed but no dice. The rad overflowed with lots of big air bubbles (not a stream of little ones) popping out - and there was no sign of coolant at the bleed valve.

Filled rad, closed it all up and ran the engine. Hoses didn't get hard. Switched off after a couple of mins, took rad cap off, switched on again. No gushing this time, and no air bubbles.

Tried it again just now, cold engine, rad cap off, turned it over. No coolant movement. It has sucked in about a cupful of coolant from the reservoir since this morning though, and there was a slight release of pressure when I took the cap off.

I wonder if I got extra air somewhere in the system after I swapped out the heater inlet hose?

Rad cap and thermostat on their way from Import Car Parts. Which means cracking everything open again, so more fun when they arrive no doubt.