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My car is a UK Diesel Honda Accord 2.2 CDTi

So I've had a problem with my car for about a week, it started overheating and not accelerating when I put my foot down on the accelerator (losing power)

I realised after the first time it happened that it's because the coolant level was below the minimum in the reserve tank

So I topped it up with about 0.75 litres of tap water and the engine temperature was ok after that, drove it a couple hundred miles over the next few days and then had to top up the reserve tank again because it was low, but the car did not have any problems with overheating or losing power

A mechanic friend brought over a pressure testing kit which he used to increase the pressure on the coolant system to 1.5 bar (the system is rated to 1.3 bar) and we ran the engine for about 20 minutes but couldn't see any water leaking from anywhere in the engine compartment, water pump, any of the hoses, radiator or exhaust

There's no white gunk in the oil filler cap, or in the dipstick so I don't think it's a gasket

I can't see and haven't seen at any time water dripping from anywhere underneath the car or in the driver or passenger foot well

Any ideas where the water could be going? It must be about 3-4 litres now over a week, the coolant system holds 6.3 litres according to owners manual

EDIT: I've ordered a UV dye and trace kit to see if that helps trace the problem, will update once I've had a chance to use it

UPDATE 28-07-2019: Have tried the UV dye for a few weeks now but still haven't been able to find the source of the leak, tried another liquid called FIXT engine coolant stop leak but I think it's still losing coolant, perhaps more slowly than before. The car itself runs fine otherwise

  • Someone at work asked if the heating has problems, which it does, for months now (maybe more than year) the heating doesn't work until the engine is warmed up and even then, sometimes it will stop blowing hot air (it's an old car so I figured some air con thingie needed looking at and I just learned to live with it) Anyway, he recommended that I bleed the coolant system since that's a symptom that there's air in the engine, so I'm going to try that and see what happens – Spikyface May 28 at 18:11
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If its not in the oil, not in the cabin, and you are really really sure its not on the ground, then it must be in the cylinders. This is consistent with the loss of power earlier this week. A leak down test could help to confirm this.

Here is a bit of maybe-false hope for you though: You don't really know for sure how long its been low on coolant. An empty overflow tank and a partially full radiator may still keep you out of trouble longer than you would expect. Considering your heater has been intermittent for months, I'd ponder that the problem has been slower coming than it seems.

The first thing to do is figure out, when cold, if the radiator is full, and how much water is in the expansion tank. From there, you can figure out exactly how much its losing over a week. This tells you either "a bunch (more than a liter)" or "just a bit(1/4 of a liter)"

"a bunch" leads you to what you already know: the cylinders

"just a bit" could lead to a re-examination of the "on the ground" possibility. Assuming the diesel looks like other Hondas from that era, there is plenty of places a small amount of fluid could pool and evaporate without your knowledge. A drip could travel along the bottom of the car for quite a ways. It might not even make it to the ground if its losing, say, 30ml a trip for the last 6 months.

Make sure it isn't gonna freeze anytime soon if you are running tap water. And whatever you do, keep a close eye on the coolant level until you get it resolved.

  • Since yesterday the coolant level stopped dropping. I drove it for 30 miles in the morning for an hour and the same in the evening but the coolant level didn't drop and the temperature was stable. I tried bleeding it but coolant immediately came out of the cylinder head bleed bolt when it was open and I started the car and it was clear green liquid so seems like coolant. Still haven't been able to find any water pooling or dripping underneath yet except under the air con tank when I use it while driving (I have photos if you want to see this). It's summer here so not cold enough to freeze yet – Spikyface May 30 at 5:45
  • Thanks for your detailed response. I also checked the heater more thoroughly, when the AC is off, the fan does blow hot air into the cabin when the engine is running, it's only when the AC is on the the heating issue happens so I don't think there actually is air in the engine. I suspect that water was dripping somewhere and evaporating because of heat OR it happens on the road – Spikyface May 30 at 13:05
  • When I'm driving fast for a long time? I'll keep an eye on it and see if it happens again. Should have a UV dye kit soon to trace leaks so maybe that will help – Spikyface May 30 at 13:13
  • @Spikyface do you happen to know the history of the car? Maybe its been low on coolant since you got it. Pouring new coolant isn't the same as pouring water in a cup. You can "top it off," but it needs to get circulated to fill all the channels. Just because the radiator is full doesn't mean all the channels are. And if you are filling through the expansion tank only, it needs to run to draw that fluid in. Maybe all it needed was to be re-filled and bled. Keep watching cold coolant levels, radiator and overflow, and see if its really stopped. 30 miles over an hour is a pretty good run. – Zshoulders May 30 at 16:16
  • Yes, I bought the car more than 10 years ago when it was four years old and have driven it since then, do I don't think it's been low since I got it. I've driven it several more times since two days ago and the coolant levels aren't dropping so I hope you're right. I'll think about if it was given to anyone or take to a garage for any reason and they might have drained it somehow. Perhaps it the issue didn't occur unless it's doing longer distances? I'll keep an eye on it. Thanks for the response – Spikyface Jun 1 at 6:05

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