[ThatstockishCRX]

Before anyone says there's a search bar to look, I've been searching and searching different forums for days now. I recently pulled a D15B2(bad seals, almost 300kmiles, burned oil) out of my 91 crx. 98% sure it was the stock motor, the heat worked great and I never had a issue with it overheating even with a 30y/o radiator. Well I found a D15B7 that came out of a del-sol on marketplace that didn't leak, smoke nor had major issues. The guy told me he ran nitrous through it a couple of times but said it was a healthy strong motor(reputable guy in my town). I swapped over my DPFI intake manifold and dizzy and thermostat to the B7 and got a new timing kit with a gates waterpump and drop her in. Did a vinager flush to get gunk out of the motor but forgot to close the heater core. After the first 3 test drives the car would over heat and the fans not come on( most likely bad fan switch, is now jumped with paper clip). Did a few more flushes to get the gunk out and took it for a ride after bleeding the coolant system. Temp was fine until up to highway speeds, spent a day chasing it and was about to replace the HG. Decided to buy a new rad( since I'm pretty sure it still had the stock one in it ) and put it in and It didn't over heat after the first few test drives. I drive it last night to work and I get into the parking lot after crusing at 75-80mph for about 7-8 miles on the highway and I look down and noticed the temp skyrocketing, I immediately turn on the heat and it blew hot air for a couple of seconds and stuck the paper clip in the plug for the fans, after doing all that she was still in the high temps so I hit the gas in neutral to get some rpms going and she cools back down to operating temp. I drive it again tonight and I get to the parking lot and sit there(fan switch has been jumped for the entire ride). 10 mins go by as im changing a brake light and I notice the temp rising a little above half way so I hop in and hit the gas and the temp goes back down. Same thing in the drive thru after getting off the high way, about 10 mins of sitting after driving the temp goes up kinda slow but not fast either. Hit the gas and set the rpms to about 2k and the temp goes back down. I'm stumped about this and have no idea whats causing the overheating.

 

[Gtmorgan]

Sounds like the head gasket.didnt seat correctly.

 

[Soul Engineering]

Sounds like too much nitrous a time or two and the head gasket is having issues. I'd put a new head gasket on it and new head bolts. Could also be bolt stretch depending on how big of a nitrous hit they were taking. I've seen the floaty gauge a few times that will run up at idle and come down with rpm. Thats generally the head gasket. Sometimes the Tstat but you have new, so. The vinegar may have caused those last remaining pieces of graphite holding hands in there to say, nope, no more, we give up. Do it right with new head bolts and it'll probably be just fine.

 

[drtalon123]

Check for head and block deck surface warpage too, otherwise new HG is just going to blow again if out of spec.

Might also want to have head pressure tested at machine shop when you get it cut back flat.

 

[transzex]

hot leak down test, likely a cracked head. it a D15B2 thing

 

[ThatstockishCRX]

Thanks all for the responses, I took a gamble and drove it 6 hours to see my family in NEGA, never once did it overheat while driving but if I sat for more than 1 or 2 minutes the temps would start rising and I would keep it at 2k rpms and the temps would come down

 

[bobski]

Sounds like a big bubble in the cooling system that settles in the head when RPMs are low. As others have said, head gasket is suspect. Just to cover the base, you tried using the bleeder on the upper radiator hose neck?