Anyone replaced thermostat and had problems getting the air out?

Noticed my fans turn on to high speed for the first time ever.

Pulled over and temperature via obd had reached 102c

Nice hot air coming from both front and rear heaters, so pump is working.

Checked for leaks around pump, nothing, and no signs of any crusty coolant deposits.

Left it to cool down, topped up coolant as it had reduced below low mark.

Both outlet and inlet hoses were cold

Took 2 hours to get the thermostat off. The nuts are a pain if you don't have the right flexibility and patience.

Have to remove idler pulley, as the housing will not come off otherwise.

Everything refitted, got it refilled and everything seemed to be good, hoses getting warm, temperature back to mid 90s.

Next day, coolant has dropped, which is kinda expected, but I've since been unable to clear some stubborn airlock.

Got the heaters back to hot, fans are screaming and radiator and hoses are cold.

I've massaged hoses, bleed air from top of engine via bleed valve, but no luck.

This morning I managed to drive it about a mile without a problem, but as soon as I headed downhill, air must have moved up to the thermostat and the problem came back.

Anyone else changed thermostat and suffered the same?

The old thermostat was definitely jammed in the closed position, and fails to open when tested.

I haven't got any specific advice, but I have heard good things about using a vacuum pump to remove all the air from the coolant system first, and then coolant is admitted. With no air to get trapped there should be no need to bleed it.

This is a kit I found on eBay, but I have no personal experience of using one LINK

I haven't had to change the thermostat on my Alphard yet but in the past, when bleeding is difficult I used a funnel sealed on to the top of the rad to bring the coolant level up, well above the head. then it allows plenty of expansion when revving the water pump. Could there be a bleed port anywhere on the system? as it stretches quite far down to the rear wheel well if i remember correctly.

I hope you installed a Toyota thermostat. I've never had luck with aftermarket ones. 2GR coolant bleed video. Should be similar. https://youtu.be/UJe1dbFVoqw?si=AET-oN19swXAOhjf

There is a bleed valve on the block of the V6, as this is a pressurised system, there is no radiator cap.

Bleeding actually was not the problem.

The actual thermostat was not correct.

The Toyota part number is listed by many aftermarket suppliers of thermostats, but beware, the majority are NOT the same as the alphard one.

The thermostat that was fitted definitely did not open the same distance, and I suspect what is happening is that the system operates as it should until a load is placed on the engine, the pump then increases the pressure along with the climbing temperature, and the water takes path of least resistance that is the unclosed bypass path, which leads to the thermostat closing and cutting off circulation to the radiator.

I ordered an official part, which took 2 weeks to arrive yesterday.

I'll get around to fitting this part this week (identical to the original that was removed).

Ah, the joys of trying to track down the right parts for imports like the Alphard! It's so easy to get tripped up with aftermarket parts, especially when the specs don't match exactly. Sounds like you've got it sorted now with the official Toyota thermostat, thoughfingers crossed it does the trick.

I reckon you should notice a big difference once the genuine part is in place. Let us know how the fitting goes and if things smooth out after that. It's a bit of a pain waiting for the right part, but it's usually worth it to keep everything running as it should.

cheers
-Tango!