Quote Originally Posted by EG52NV View Post
Looks like car is juat getting hot coz its being pushed, and my last option is investing in a low temp thermostat to move the hot coolant out of the block sooner!

But aren't these bad for daily driven cars?
Na low temp thermostats are fine as long as you don’t get one with an extremely low opening point..
Stock B16/18 open at 87-90c from memory, just get a 87c or 82c unit if you’re worried but they go all the way down to 65c I think.
Sounds head gasket related to me and possibly why the previous owner ran without a thermostat

Bubbling out of overflow bottle can point to a leak/break in the head gasket between the blocks water pipes and one of the cylinders... this type of leak can sometimes only show-up after long driving due to heat soak/build-up and not show-up on small runs even if you hit it hard.
This type of leak pushed hot air from the cylinders into the cooling system and does two things.. one, added heat and two, added air the cooling system than needs to be pressurized to work correctly and thus pushed coolant into the overflow bottle

Things I’d do:

1. Get a low temp thermostats (82c)
2. Make sure your radiator fans connected and working correctly (if not working unplug the fans two pin socket from behind the thermostats and bridge two pins with a paperclip, this with trick the fans into running the whole time but it’s only a temp fix.
3. Make sure you don’t have too much coolant in your system, more water the better in fact.. 10-20% coolant the rest plain water!
4. Make sure the radiator cups sealing and it’s the right pressure spring for your setup.
5. Check for leaks in the water hoses.
6. Maybe get a radiator pressure test a flush.
Remember the cooling system is designed to work under pressure and any leak or air bubble will affect its ability to work correctly and cooling efficacy

Quote Originally Posted by tiksie View Post
Just run no thermostat!
Engines are designed and setup to run with-in a certain heat range for optimal performance and longevity, the cooling system needs to be configed to handle all the different variations.
Not running a thermostat means you actually have no control over the heat/cooling system and temps will fluctuate quite a bit, especially as it’s a daily driver and that’s bad.
Track cars can kind’a get away with no thermostat if needed as they’re being run hard the whole time and need to displace big heat, I’ve been told that it’s very hard to tune a car without a thermostat due to the big temp fluctuations I’ve just mentioned..