A little history of my civic; it’s a 97 dx hatchback with the stock d16y7 mt. The car only has 69k on it and it’s my daily driver, a few months ago it over heated due to what I believe was the original radiator going bad. I was on my way home from work on the highway and just happened to look at my temp gauge and it was in the red. I immediately pulled over and shut off the engine but kept the heat running. I sat there for a minute or so and turned the car back on and the temp was normal again so I made it to a gas station without it over heating again. Checked and the radiator was co covered in coolant. They didn’t have any coolant At the gas station so I filled it With water and drove home. Replaced the upper and lower hose and radiator and everything was good again. About a month after that I rearended someone and resulted in my front passenger side being pushed in. Drove it home 50 miles with no issues. Fixed the car myself with two new headlights, new hood, rad support and front passenger fender. The new radiator was bent just slightly but wasn’t leaking so I reused it. Fast forward to today when I just finished putting it all back together. Took the car out and it was running great until it got up to operating temp. It started surging at low rpms (below 2500) when I would put the engine under load. It was like it’s being starved of fuel and shaking the car. Get it above 25000 rpms and it runs great. Get it home and I thought it was the ground that goes from the engine block to the rad support. I thought maybe the new support was too thin of metal or something coming from China. So I bolted it to the chassis and took it out again. No luck. I thought maybe the radiator cap got damaged in the accident. Replaced it. No luck. I thought there might be air in the cooling system so I parked it on an incline and put it on jack stands to get the front up more. Took the radiator cap off, turned on the heat to max, and ran the car for about 15 minutes. No bubbles really came out, it just overflowed. I should mention I don’t believe it really got up to operating temp doing this. It’s cold here in southern pa. So I don’t think the thermostat opened. I closed it back up and took it for a drive. No luck. Came back and noticed there were a few bubbles coming from the tube in the overflow coolant. They stopped and I haven’t seen them since. (Went on one more drive after that). Also I noticed that the top radiator hose is hot like normals but the bottom one is cold. I couldn’t remember if that was normal. The tail pipe is dry, no signs of leaking coolant anywhere, oil looks fine. I’m at a loss. Any help would be GREATLY appreciated. Idk if it could be distributer related or air still in the cooling system or head gasket or electrical or what. It baffles me that it runs great until it’s warmed up and then only under 2500 rpms exactly is when it’s surging. Thanks to anyone with advice.

would that cause it to surge only under 2500? And how would I test that? Thanks!

I should also note the CEL isn’t on

not sure... haven’t checked for codes yet

so far today, I purchased a coolant funnel, put the car up on ramps and tried to properly bleed the coolant system. Had the heat set to hot and engine running, when it got up to temp, it just started boiling. Fan never kicked on. I then pulled the plugs as seen above... they look uniform to me. Maybe a little lean? They go left to eight cylinder 4321. Then to see If the fan is working I jumped the t stat housing connector with a safety pin and I could hear the relay switching on and off but fan didn’t come on. I then ran two wires directly to the battery and thouched the fan positive and negative leads. Fan kicked on. Thoughts?

how can you tell the plugs weren’t tight enough?... they were very easy to get out. I fixed the fan not coming on... tracked it down to the fuse being blown. Haven’t checked the iac yet and can’t find any vacuum leaks. I found on another forum a guy was having the exact same issues as me, turned out to be his o2 sensors...

ah lol. Yea I thought they were too easy to remove... and ok thanks! ... unplugging them won’t make it surge more? Or would it just throw the cel? Thanks for the reply

awesome, thanks! I’m going to give it a try

haven’t touched that yet, that will be next if the o2 sensors don’t fix it.

awesome, thanks man. I’ll give that a try after I test out the o2 sensors... I’ve been reading a bunch of people with the same issue find luck in just disconnecting the o2 sensors first and seeing if that helps it at all... would the iacv have to do with the rpms under 2500? That my main issue. After 2500, it runs great.

it actually idles very low after warmup. Doesn’t fluctuate too much, but it idles very low. Almost like it’s gonna stall

lol I plan on trying it all. Starting with unplugging the o2 sensors and going for a drive. Seems like it’s rhe easiest to start with. Then going on to cleaning the tb and the Iacv. I’m at work now so I’ll do it in the am and report back. Thanks

Went home this morning and disconnected the o2 sensors then went on a 20 mile drive... no surging and the engine was idling great! But then I felt the radiator hoses and they were extreamly hard. Couple days ago I bought a new rad cap and it did it with that one too. The day before that, the top hose was hard and the bottom one was cold and soft. When I squeezed it, it almost felt like it was going to collapse. Bad thermostat?

really? They get really hard. I thought you should still be able to squeeze them

yea the cap that’s on there right now is the one that came with the radiator from Napa. It doesn’t have any number on it. The cap I just bought the other day from car quest has 1.1 stamped on it but the hoses also got very hard with that one too. I ordered a new oem thermostat since I never changed that when I changed the radiator and on Tuesday I’m doing a combustion chamber leak test to see if it’s the hg.

A little update... I did the combustion chamber leak test and all seems to be good there so I don’t think it’s hg. There seems to be a big difference in temp and pressure between the top and bottom rad hose so I’ve got the t stat ordered. Car started surging again even with the o2 sensors unplugged. Popped off the distributer cap and there is a lot of moister and rust built up in there. And no o ring to properly seal it so I’m hoping that’s the cause of that. I read on another forum of a guy having the same issues as me, Gus was due to water in the distributer as well so we’ll see.