Slow Coolant Leak

I picked up my 03 C2 in January and have only been able to drive it 3,000 miles. It's a saga to say the least. 70K miles on the chassis about 70K on a donor engine transplanted in 3K miles ago I've put more than a gallon of coolant in it It slowly goes down, but is consistent No chocolate milk in the motor oil Had the transmission out for clutch replacement 2K miles ago Did a thorough inspection of the car front to back with under carriage covers off My friend who is a mechanic also looked and we can find any sign of coolant leaking I had the front bumper off and cleaned the radiators. No sign of leaking there. Any ideas of where the coolant could be going? The only place I can think of is inside the engine. Thx for any insights you may have!

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Have you had your mechanic pressure test the system ?

Combustion Chamber . . . Cracked Casting &/or Defective Head Gasket. Easy way to check for this. Search Google for <Exhaust Gas in Coolant Test> there are any number of "kits" for ~$30 that will allow you to identify this. That said, if you can't see or find where it's going elsewhere, this is probably it.

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When the engine was replaced, I assume you flushed and refilled using an airlift system? If not, this may be normal for the car to push the coolant through the system. While it may seem like it's "leaking" out, the water pump is pushing it through the entire length of the car included areas like the heater core. The tank level will go down as air bubbles are released through the pressure valve on the expansion tank. If you're not getting any puddles on the pavement, I wouldn't worry. Just keep the levels normal.

Also check the coolant reservoir and cap.

You should pressure test the system correctly, system pressure test to 18.85 psi, cap test to open at 20.3 psi and close at 14.5 psi.

Are you getting a "sweet" smell from the exhaust? If the missing coolant is being burned up in your combustion chambers, you would typically get a "sweet" smell in your exhaust gases, most notably upon shutdown of the engine. If so, that would indicate a cracked head or cylinder, or a faulty head gasket, which are allowing coolant into the combustion chambers. A pressure test of your cooling system, as previously mentioned, should be your next diagnostic step. Best of luck.

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The engine swap was done by Deman Motor Sports https://demanmotorsport.com/ . My guess is that they did this. Good thought as we initially thought the same thing. I've added 7 liters of coolant in 3000 miles. I feel the need to reach out here and figure out what's wrong.

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The good news is that there is not any white smoke coming out the exhaust and no sweet smell there either. I've been looking for exactly these signs. Thx! heading to NAPA to get a pressure tester today.

Also keep an eye on your oil level and make sure it's not rising.

Not sure if mentioned above. Lay on your back and look up the left wheel well for any chaulky white residue. If so, leak. Could be tank, could be hoses or more likely a connector. I would pull the air box and look under the coolant tank too. Hopefully just air pushing through the systems which would reduce the level. I replaced my coolant tank over the winter. With that said, if I can do it, anyone can. Best of luck.

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Hate to say this but 7 liters in 3k miles is not a small leak, its a problem. Im laying odds it has a cracked head and i would tell that shop to come pick it up with a tow truck.

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What we know is he's not getting intermix in the coolant nor the engine oil. No smoke. He's confirmed there are no coolant puddles or obvious leaks around the car when sitting. My bet is the shop didn't flush and refill properly. Remember, these cars hold 22 liters of coolant. Personally, I don't think his situation is absurd considering the circumstances. But we'll see.

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Well we really dont know much except fot a visual observation. My point is that for what one of these engines cost i would not be driving the car. Either do a proper flush and monitor or do some proper diagnostics to confirm there is no issue internally. Either way im sure a pretty penny was spent in the motor swap and i would send it back to verify the motor they put in is in good shape. If the shop didnt drive the car enough to notice it was missing 1/3 of its coolant.... what else was missed?

I borrowed this tool from NAPA today. Drove the car there and then it sat all day. When I pulled the cap off it still had a good bit of pressure that needed to be released. I would have preferred no pressure as it would point towards a leak. I didn't attach the tool tight enough the first time & it popped off spraying coolant everywhere Going to let this sit.

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This is exactly what we thought and I'm hopeful that this is the case. However, I keep topping it off. Hence the reason I reached out to this group. I would also be very happy to replace the coolant tank. Seems like a regular thing given that it bakes on top of the exhaust. I need new motor mounts anyway and if I lower the engine I'll do that job at the same time. Thank you everyone! I'll let you know. With gratitude.

After u pressurized the coolant system did the needle on the gauge move after an hour or 2? If so u gave a leak. The pressure needle should be in the same place after 2 hours. The fact that it still gas "some" pressure means it may just be a small leak. If the needle dropped and u cant see fluid drips anywhere then the leak is internal. If the needle didnt move at all thats a good thing and the system us sealed. this kit will detect combustion gases in the coolant. It would indicate a cracked head as the head gaskets dont fail on these motors. Amazon Amazon

The update: there is a leak. No surprises there. Pressure falls in about 3 hours. No exhaust gases present.

I guess it's the coolant tank. I've looked all around with a flash light and there are no usual tells about a leak. Although you'd think with 7 liters, and counting, of coolant it would be pretty obvious. Thoughts? I'm fine replacing the coolant tank. While I'm there I'll replace the motor mounts. I'm also getting a Secondary Air failure code. it's probably vacuum related and I've replaced everything that I can get to easily. Is there any space advantages with the tank removed that would make the removal and replacement of the secondary air injection check valve easier? If I can get to all of it I'll just do both of those jobs at one time. Thanks for the comments!

Now with the proper tests u now have a direction to go. 3hrs to loose that amount of pressure is a pretty small leak. U may actually be steaming the fluid off and thas why u r not seeing fluid. U are gonna have to get the coolant up to temp and do some investigating. If u want to isolate the tank u can get some clamps and close the hoses. This would be my next step before i bought any parts. Also what is the secondary air code u r getting. cheap example of the clamps Amazon Amazon

Could it be a leak at a hose on the oil cooler? That�d explain why you never see it. It might be gassing off at the front of the engine (just above the transmission) and you�ll likely never be able to visually detect it otherwise.

Replace your cap and check the overflow hose. Mine was laying right on the first ignition coil and venting periodically like you describe. I found it by smell and refilling and finally coils misfiring and when remove They were showing coolant hit them. I replace the cap and lengthened the hose to vent to the ground and not the engine area.

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Its not his cap. He presurised the system without the cap and it leaks down.... although the cap may still be bad.

Get a cheap bore scope and you'll find the white residue...

I have those tools (pressure tester) and a few psi of leak after 3 hours is ... not a leak. If you do not have a good seal at the top of the tank (where the cap screws in) you would probably lose a few psi in 3 hours. I would first replace the cap, then the tank. Replacement of the tank is not a simple DIY.

Thanks for the conversation! I had the transmission out earlier this summer, 2000 miles ago. Looked the entire engine over from the back side as well. See below. Debated on replacing the oil cooler and actually bought one and had it in stock when I did the clutch. After a thorough examination I decided not to do the oil cooler job and sent the parts back to FCP. With the transmission out and all the under carriage covers off the entire car was combed over for leaks. We did not find any. Coil packs and plugs replaced 3,000 miles ago in May. Did not notice any leaks. Replacing the coolant tank is not big deal for me and it's one of those jobs that will need done eventually. I'd like to diagnose the real problem to be sure. I could replace the tank, again not a problem, but still be left with the original leak. 7 liters in 3K miles seems like a lot. the CEL is a P0492 Secondary Air Injection system, Bank 2 malfunction. I replaced vacuum hoses & a Y splitter while I was in the back of the engine. Replaced all the vacuum hoses I could get to with out taking anything apart from the front. Still getting the CEL. If taking out the tank would buy me some room I'd be wiling to replace the vacuum system entirely while I'm there. However, It doesnt seem like there would be much more room with intake manifold between the coolant tank and SAI check valve.

Pick up some coolant system dye. It will make it much easier to find the leak.

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Hopefully you can get the black light to the source of the leak.

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good idea. I've got some in stock & a UV light. Slowly working through the process. Thank you for the help!

When I replaced some coolant hoses I didn't tighten one of the screw clamps properly(big hose that exit the engine). The engine started leaking quite a lot when it was hot, which I noticed when I did a stop on my test drive, and looked underneath the engine. 20min later at home all I could see was some white residue on the tube, there was no obvious wet parts or leaks after parking.

3 hours to lose about 5psi. Wouldn't that fall into the territory of normal pressure bleed off? Typically if you're looking for a cooling system leak via a pressure tester you're looking for a leak down rate of 1 or 2 psi loss every few minutes. This has me wondering if the system was just low on coolant from from years of being driven and the reservoir not being checked. You lose a bit of coolant every year from just normal operation.

Here is the update and the solution to this slow leak problem. I did put some UV dye in the cooling system. Got it from NAPA and was particular to the cooling system. I had some UV dye in stock, but it was for oil, transmission, and power steering systems. Ran it for 75 miles and still couldn't find the leak. However, I did get a bunch of cool UV pix of the engine. The only dye that lit up was some splash around the coolant tank. I dismissed it because I knew I had spilled some. During this process I also dismissed splash around the overflow tank because I thought I hadn't tightened the cap enough. Then a buddy of mine read the part number on the cap. It was a .01. I mistakenly thought that because it was blue it was the updated version. In all of this I never read the part number of the cap. That said I ordered a new cap and I've been driving the car for several hours and a couple hundred miles with a constant coolant level. Sorry for missing this, but I'm very happy with the support from this group. It was clearly brought up early the conversation about the cap, but I thought I had that sorted. The good news is that I feel pretty confident that it was the cap. All the other possibilities were eliminated. It's also a pretty difficult thing to diagnose in that I kept dismissing the cap being the problem because I spilled coolant or didn't tighten it enough. Thank you gentlemen! What a cool group. pun intended.