Hi all,

I've got a stock Civic Si (D16Z6) with a cold running problem.

When I start the engine from cold:

- For the first minute, if I rev the engine I can hear it hesitating slightly, like there's a timing or ignition problem, but after a minute the problem goes away and the engine revs up smoothly.

- For the next 5 mins, whenever I stop the car, i.e. take my foot completely off the gas, the revs plummet past the idle mark, the engine nearly stalls (couple of times it has), then bounces back up to a normal idle.

Other symptoms:

- Losing coolant - I have to completely refill the expansion tank every couple of weeks.
- Running cold - According to the temp gauge, which never gets above 1/3 - used to run at a steady 1/2.
- Slight petrol smell - Not that bad but just about noticeable in the cabin at times.

My first thought was a leaking head gasket so I ran a compression test:

Cylinder 1 - 225 psi
Cylinder 2 - 220 psi
Cylinder 3 - 215 psi
Cylinder 4 - 210 psi

Anything to worry about there? All 4 cylinders are well above the standard 184 psi, which I assume is due to carbonisation as the engine's done over 150k - would that make sense? There's also a 15 psi difference between cyls 1 and 4 - does that tell us anything?

Or perhaps I'm way off base - any thoughts and suggestions would be much appreciated.

Thanks in advance,

Rob

 

i have a d15b7 but if i remember right there can be up to 25 or so psi difference between cylinders. or like 18% somthing like that its in the hayes manual. as for the head gasket im not sure i just know it will drive like crap( no power) if the head gasket goes bad and smoke alot out of the exhaust (from burning coolant) the exhaust will also have a sweet smell. any leek that you can see? warm you car completly to operating temperature and then check for any leaks. the ruber hoses expand when they get hot so a crack may only be noticable or leakwhen hot. also look around the head for coolant when its hot to check for leaky head gasket. you may not be leaking into the cylinders so no smoke but it may be leaking out the outside of the head

hope that helps a little

 

Is white smoke coming from the exhaust?

Can you detect a coolant leak anywhere?

Also, your thermostat may be stuck open.

 

Thanks for the replies.

The compression test results are basically within spec, it drives fine (when it's warmed up) and it's not smoking, so it's looking decreasingly likely it's the head gasket.

Had a look round underneath when it was warmed up and running and couldn't see any leaks.

RonJ, you reminded me - when I was bleeding the cooling system I ran the engine with the rad cap off and noticed that water was flowing through the rad - from cold.

Would that point to a stuck thermostat? I guess it'd explain the rough cold idle and low temp reading, but what about the lost coolant?

 

Yeah, sounds like a stuck open thermostat. Try replacing.

With regard to the lost coolant, it has to be going somewhere. If you're not burning coolant, then you have a leak somewhere. Check all engine coolant hoses, connections, the area below the water pump, and the heater core inside the car.

 

Thanks - I'll give that a try.

Thinking about it I only seem to be losing the coolant from the expansion tank, whenever I've taken the radiator cap it's always been full to the brim and the engine isn't overheating at all.

Any idea why that would be? Could I be losing coolant through the rad cap?

 

It could be leaking from the reservoir, though you should be able to detect such a leak. Alternatively, you have a leak somewhere else in the engine cooling system, causing the system to draw coolant from the reservoir.

 

OK, I replaced the thermostat.

The good news: Coolant now only flows through the radiator when the engine is warm.

The bad news: It hasn't fixed my cold running problems - idle is still weak, engine still runs cold, and the petrol/exhaust fumes are so potent they gave me headache - and I'm working on the car outside!

I noticed something else when replacing the stat. With the radiator cap off, the coolant flows normally, but if I rev up the engine it bubbles and swells out of the filler neck - is that normal when revving the engine or does it point back to a leaking head gasket?

 

Could be exhaust gases entering the cooling system due to a bad head gasket or cracked head.

 

Hmm... I dunno.

Some people say water pushing back while revving is normal, others that it's a sure sign of a leaking head gasket.

I'm also getting some (not much) white smoke, even when the car is warmed up, but it is a bit cold here at the mo - around 40 degrees. Again, normal or a sure sign of a blown HG?

On top of all that I've just noticed I'm getting a whooshing sound from the muffler under heavy acceleration - another pointer to a bad HG or just that my muffler is on the way out?

So confused!