Ok here is the prob. Just finished building a new motor and I am now breaking it in. It was fine for the first 1000 miles. I had a small leak coming off one of the hoses on the iac. I fixed it and it stays dry.Now after running it on the highway when I come to a red light the temp gauge starts to climb. I have went over it three times looking for a pinhole leak or anything. My radiator and overflow are right on the money. The gauge never goes past 3/4 of the way up. It goes down once the fan kicks on and then will climb back up if I let it sit to long. It was fine for three days after I bled the system. I have all new hoses and new termostat. The heater core hoses dont get very warm or the hose coming off the control valve.Also when I turn the heat full blast to help bleed the system it doesnt blow as hot as it use to. Both upper and lower hoses get hot as well as the hose that connects to termostat. The car is a 98 hatch with a built itr. I still have the stock cx radiator. Could that be causing the bad flow of the coolant making it run hot? I had a gsr swap with bolt ons and never had this issue. Any help would be nice. Thanks.

 

It might be the water pump going out, air bubbles trapped in the system(happened to me). What does the build consist of? OEM rebuild, or high compression? What ecu/tuning? Is it running lean?

 

Probally has a air pocket i would check that and check your thermostat.But if its all new not sure its going to run a little on the hot side until everything seats.

 

The build is: Gsr block with 81.5 rs machine itr pistons,recond gsr rods with arp bolts,polished crank,all new bearings. The head is itr with skunk tuner stage 2 cams,skunk gears,skunk springs and retainers,st flat head valves,arp head studs,oem itr water and oil pump,all brand new oem gaskets. The head has the normall port/polish and valve job. It also has all new heater related hoses and a new oem thermostat. I have bled the system 3 times and yes bubbles did come out for a while and then stopped. I am kinda thinking its that stock cx radiator. It is from 98 and is prob meant to cool a stock single cam. Like I said both heater core hose are not getting very warm or the heater control valve hose. It has a mild street tune on chrome. Vtec is set at 6000 for the break in. WOT is 13.1-13.4 on my aem. Oil psi is 63-78 on the gas.

 

I would get a fluidyne but it shouldnt be over heating its only 81.5 gsr.

 

Rad. could be clogged, check to see if the hoses are hot on both intlet and outlet of the rad. Also, make sure you bleed it completely, I bleed mine 6 times before I got all the air out and solved my overheating issue. Squeeze your rad. hoses to help get any air out.
Do a compression and leak down test, might have a bad head gasket or burnt valves. Were the valves adjusted, head studs retorqued after 10 heat cycles?

 

Thanks for the info. I am done bleeding for now. I have a new rad with thin fan on the way, plus a J's rad hose set,j's fan switch,j's cap,and thermostat. I will then redrain and flush the whole system. If all that doesnt solve the issue then its what I dont want it to be. Blown headgasket! Ill keep it posted.

 

I had the exact same thing happen when changing coolant 1 time. Your heater issue is key, no heat indicates you probably have an air bubble trapped. I installed a radiator flushing tee in the top of the highest heater hose, sure enough the overheating and lack of heat gone.

 

Ill try that once I install all the new parts. Might as well flush the whole system while I am at it. Thanks for the info.

 

You didn't answer all of my questions,
were the valves adjusted properly, were the head studs retorqued after 10 heats cycles like ARP recommend?

 

I vote air bubble in system also. I had to fix that gremlin before, and it was very time consuming.

I bought a Lisle 24610 Spill-Free Funnel off Amazon, this works great. The key is to start the car from full cold with heater all the way on (fan speed is irrelevant), keep the coolant level in the funnel at about 2/3. Run the engine up to operating temp (fan will come on), then hold at ~2,000 RPM for 2-3 minutes, this circulates the water with enough speed to force out the air trapped in the heater core.