I've recently done head gasket, mild head rebuild.

Has been running well for 3-4 weeks, no oil loss, no coolant loss.

I have a 1.6 but with a retro-fitted colour dash, the temp gauge moves normally to 12'o'clock position (90c) and stays there the whole time, which I don't quite trust as OBD2 has showed fluctuations up to 94c in the past...though I haven't actually tried it recently.

Anyway, the other day I noticed I had no water pressure after a drive. Coolant was hot and was higher in the expansion tank than when cold but all looked normal. I've had no coolant loss so I assumed I had a faulty cap, and I was just lucky not to boil over the coolant.

Anyway, new cap arrived today, but it hasn't solved the issue. I definitely had pressure when hot before I did the head rebuild (issue was leaky exhaust valve, no issues with head gasket).

Anyway, I'm stumped as to how to test, what to look for next etc. I don't like that it isn't pressured, so I don;'t want to drive too far currently.

If you are not loosing coolant then either there is no issue or the engine is running too cool. In ths case the coolant isn't getting to boiling point at atmospheric pressure, even in the hot parts of the engine. This could be caused by a stuck open (or missing) thermostat or possibly mis-routing of coolant pipework.
First thing is to get Multiecuscan on the car and see what that says the coolant temperature is. If you want to check the system for holding pressure you can get a pressure test kit that is a header tank cap with a fitting for a hand pump and gauge. You can pressurise the system cold and check for leaks.

Robert G8RPI.

You should be able to pull the cap after the engine is warm and have it hiss with pressure, being a sealed system. Sounds like you're not getting that.

The fact that you're seeing a temperature is promising. I dont know where the temp sender is on a 1.6 (its in the stat housing on my 2.4) but they're usually around the same place. Centre of the gauge is 90 deg, which is operating temp, so the fact you're getting to and not exceeding operating temp is good sign.

I'd expect that if you werent properly circulating coolant you'd see abhorrent readings on the temp gauge, either wildly high or unrealistically cool. You're showing pretty normal so good sign.

You can do some simple checks to see if you're circulating coolant, which are pretty simple to perform.

As the car warms up, feel the top radiator hose. Once at running temperature that top hose should get nice and toasty.

You can follow that through and see if you feel the bottom hose getting warm. If you're circulating coolant properly the bottom hose should get warmer, obviously not as hot as the top having gone round the radiator, but it should warm up.

The next obvious one is turning the hot air on. If you don't blow hot air the hot coolant isn't getting to the heat exchanger - which is a bad sign.

If you're not moving coolant then the answer can only be the water pump really. They do seize and I've known impellers to fall to bits too. I dont know the specific design for the 1.6 but a lot of impellers are plastic, so simply crumble after repeated heat cycles. They can look perfectly fine from the outside but be dead inside - much like my wife

using Torque (OBD2 bluetooth), the temp built steadily on the way to work (6 minutes) hitting about 90 as I arrived.

On first run after rebuild, top hose remained cold for a bit longer than I expected (the one activated by the thermostat) but after a longer run it heated up fine.

I was going to change the waterpump but couldn't get to one of the bolts...needed an offset spanner which I didn't have in that size, typical. The waterpump is not on the timing belt though, so I can change it at a later date.

I'm getting flow into the expansion tank via the small top tube, and as there's no boiling issues obvious, plus the steady rise in coolant temp over the journey this morning, I think the pump is working ok.

I bled both places during the rebuild, and get hot air in the cabin.

Having coolant tubes mis-placed is a possibility, though I think the only ones I dismantled that could go on wrong are the front top and bottom hoses to the thermostat housing, but again, I'd expect boiling and gurgling and pressure build up if something wasn't getting flow?

I think you're right about doing a pressure test, though as I want to test the cap I think I need to add in the pressure somewhere else, maybe make a fitting or something. I have a compressor and leakdown kit so maybe there's some scope to do this with a single fitting of some kind.

One last thing, both my old cap and new cap screw right to the bottom of the thread where a sticky-out bit on the cap catches and stops the cap turning more, but the old cap never felt like it encountered resistance (like a rubber seal being squished) and the new cap has the same resistance all the way (due to new threads I suspect). I'm used to caps that feel like they've encountered resistance but the stilo one has the inner part with the O-ring so I guess that's where the seal should happen? What's your experience of this?

Thanks for your input g8rpi and Artemis, let me know if you think of something else.

Apart from the coolant header tank cap not hissing when you open it (hot.. but be careful with that... ) it sounds completely normal to me.

Your car warms up to mid-way (88C)... so the thermostat and the temp' sensor are okay.

The temperature doesn't continue to increase, so the water pump and the radiator are okay and there's no air lock.

The Stilo cap is as you describe. It seems to wind down and the "lock" via the notches on the cap, rather than pressure up as the rubber cap gasket is clamped down. Anyway, your cap is new, so let's assume it's okay.

The only thing left is the expansion tank. Has anyone interfered with it, where the cap O-ring seals in particular? Is it a Stilo tank and not something from a Toyota Avensis or something?

On the other hand, tanks don't wear out. Drive the beast around all weekend as usual, without touching the cap. Then on Sunday afternoon with the car cooling down after a good drive (so it's been hot) and with all the relevant safety gear (long gloves on your arms, safety spectacles and a wet rag over the cap) just unscrew it to break the seal and listen for a hiss.

My old JTD doesn't do the usual boiling out like a normal type tank and cap does.. it just makes a quick hiss and it's all over. I suspect yours is the same and you imagine it's not normal whereas it might be.


Ralf S.

I'm checking pressure by squeezing the radiator top hose, which has no extra pressure and easily pumps coolant into the expansion tank.

The tank looks like every other Stilo one I've seen, plus it retained pressure fine before the rebuild. Or was there something iffy that I fixed without realising during the rebuild that means the cooling system is just running better? I guess a leaking exhaust valve will heat the ports up higher than normal so maybe this was boiling some coolant in a specific place?

Thanks for the info about the cap, puts mind at ease I guess

I only had a very stiff top hose (ooer! ) when a head gasket went on my old Alfa v6.

That wasn't a usual "oil in the coolant" job - instead I was getting gas in the coolant, which forced the coolant out of the radiator and then pressurized the top-hose. Eventually the car over-heated (since there was only air, not coolant, in the radiator) and the displaced coolant ended up exiting via the expansion tank cap, as designed.

I'd say your rebuild did something to remove air (or gas) from the system and now it's all ship-shape, whereas before it was probably suffering from some gas.

It sounds pretty much like mine (just small hiss when you remove the cap from a warm system) and my beast has had a new thermostat, water pump and radiator the last couple of years and it's always behaved like it does now.


Ralf S.