got an ls/vtec swap in an eg coupe. recently got a bigger radiator and bled all the lines ocrrectly. when driving at low RPMs the needle doesnt move past about a 1/4 as soon as vtec pops the needle goes right to the top and stays for a bit then slowly makes it waty back down staying at 3/4...any ideas? thermostat maybe?

 

Any gas bubbles seen in the coolant or white smoke in the exhaust?

 

well are two hoses the same temperature? could signal u to the thermostat? did u torque down the head gasket correct? when was the last time u changed ur pump?

 

what Water pump are you running with your setting? I heard if you use and LS water pump with 19 Teeth, it spends to fast causing air bubbles and overheating issues. If you change to GSR/B16 with 22 teeth remember you have to change your timing belt to an GSR/B16 with more teeth then the LS.

 

the teeth wont make it spin faster on the water pump. it would be the size of the pulley being used. so if the overall diameter of the pulley is bigger or smaller then i could see it spinning faster or slower.

the water pump is completly submerged in coolant so i find it hard to beleive that you will be sucking in air bubbles do to spinning to fast. your cooling system is a sealed system so the only way you could bring in air bubbles is if you have a leak somewhere.

i could be very wrong on this but this seems logical.

if tempature is risng and falling and you JUST worked with the cooling system tehn the most common cause is an air bubble liek ron stated. start with bleeding the system and keep adding fluid whenever you can since your driving the car still. those air bubbles will work out eventually overtime but bleeding the system will work faster and safer for you.

heat is the enemy of motors so if your running "hot" your basically hurting your motor.

 

Water pump installation. It would be to your advantage if you went out and purchased an OEM ITR/GSR (P72) water pump. But, if you use this water pump, you must also use the ITR/GSR (P72) timing belt. If you use the LS water pump, use the LS timing belt. The P72 water pump has 22 teeth as opposed to the 19 teeth on the LS pump. This means the GSR/ITR pump spins slower at higher RPM's, and vise versa. You may think this is bad, but it is good, because at those higher RPM's with an LS water pump, you will theoretically be spinning the pump so fast, that it doesn't even push water; it just creates bubbles (cavitation). Get it? Ok, so take your water pump now and spread a bead of RTV in the gasket groove, and then slip in the gasket. Bolt up the water pump and torque down to specs. Tighten them down in a criss-cross pattern as you would lug nuts. Torque to spec. Do not overtighten as you can warp the pump or crack it, possibly even strip the bolts. Bad.

https://honda-tech.com/forums/all-motor-naturally-aspirated-44/how-build-%22reliable%22-lsvtec-b20vtec-1676914/
Scroll 1/4 down to the waterpump area.