Ok it happened since I changed the thermostat.

I idled the engine for 30 seconds to check the thermostat to see if it was working.

For that period there was no water in the engine block since the thermostat was blocking it.

After the engine air in the head heated hot enough it let the water in that was only warm.

Now I'm thinking what could have that done to cause bad idling and almost stalling and an engine sounding rough like when you get the firing order incorrect.

may sound stupid, but is it the right one, or is it upside down, coz it could be the wrong way, thermo is like a none return valve (cant spell) will only let it go in 1 direction, and diff cars have diff tension on the the spring so can be to much pressure on spring so no coolant can get though

coulda done alota damage but i doubt 30 sec would have even got the water warm enough for the thermostat to crack, why dident you just throw it ina pot of water?

?????

I filled it up through the surge tank.

It never occured to me that the thermostat would block it.

I believe it's in the right way, the spring is facing down

was there an airbleed valve on the thermostat, like a hole drilled out and a peice of wire poked through it and flat on the ends (sory about the poor description) or was it solid with just the thermostat valve?

Thermostats only work when they are submerged in water. They can not be tested inside a engine. You need to put it in a kettle with water on the boil with a therometer in it to see at what temperature it opens at. If the engine idles down really quick it sounds like damage has already been done. Drain the oil and look for metal shavings. It sounds like something has grabbed and let go. Sorry!?