Coolant system pressurising
Discussion
Morning all,
I have an issue with the Honda K20 (civic type r) engine in my Ariel Atom. Driving on the road everything is fine. When driven hard on track, the coolant system is pressurising. The coolant level in the expansion tank rises and eventually leaks out of the cap. Air was present in the radiator at the front of the car (I opened the bleed bolt in the top of it). I tried a new cap but the symptoms persisted, I then drained and refilled the cooling system. I got a garage to do a sniffer test on the expansion tank for combustion gases as I feared head gasket woes. The car was left running for around 20-30mins and the fan was kicking in, so up to "normal" temp. No trace of combustion gases were present. They suspected I had had an air lock that had been resolved when I drained and refilled. Went to another track day and after the first session, I checked the expansion tank; the levels had risen to the top again and coolant was escaping out of the cap, air was again present in the radiator. Letting the air out the rad causes the coolant level in the expansion tank to drop (with the expansion tank cap off).
I took the car to a local trusted garage and got them to bleed the system and do another sniffer test. Again, no trace of combustion gases present. I got the car back and drove at 70mph in 3rd gear for a few miles, with some hard acceleration when appropriate to try and simulate track conditions as best I could given the constraints of driving on the public road. The coolant level started to leak out of the expansion tank cap. I let a load of air out the radiator and the coolant level in the expansion tank dropped back to normal. I immediately repeated the test and got exactly the same results; another load of air in the radiator and coolant leaking out of the expansion tank cap. Bubbles were visible periodically rising in the expansion tank.
At no point did the coolant temp rise above "normal" readings, and driving "normally" for road use the problem does not manifest, it only happens under hard use.
I'm not sure what to do next. The vehicle has a mechanical and electrical water pump. The electric pump is working, and I assume the mechanical one is as well. The fan is operating normally. My gut is saying it's a head gasket issue causing the coolant system to pressurise, but the lack of gas detection on the sniffer test goes against this. However, the sniffer test has not been carried out after "hard" use. Is it possible a dodgy head gasket can only leak combustion gases under hard use and not "normal" use? I'm wondering whether to change the thermostat, but I don't see how that would cause air to forum in the top of the radiator?
Any help or advice welcome, got some charity days coming up soon so need to get this resolved!
Cheers
I have an issue with the Honda K20 (civic type r) engine in my Ariel Atom. Driving on the road everything is fine. When driven hard on track, the coolant system is pressurising. The coolant level in the expansion tank rises and eventually leaks out of the cap. Air was present in the radiator at the front of the car (I opened the bleed bolt in the top of it). I tried a new cap but the symptoms persisted, I then drained and refilled the cooling system. I got a garage to do a sniffer test on the expansion tank for combustion gases as I feared head gasket woes. The car was left running for around 20-30mins and the fan was kicking in, so up to "normal" temp. No trace of combustion gases were present. They suspected I had had an air lock that had been resolved when I drained and refilled. Went to another track day and after the first session, I checked the expansion tank; the levels had risen to the top again and coolant was escaping out of the cap, air was again present in the radiator. Letting the air out the rad causes the coolant level in the expansion tank to drop (with the expansion tank cap off).
I took the car to a local trusted garage and got them to bleed the system and do another sniffer test. Again, no trace of combustion gases present. I got the car back and drove at 70mph in 3rd gear for a few miles, with some hard acceleration when appropriate to try and simulate track conditions as best I could given the constraints of driving on the public road. The coolant level started to leak out of the expansion tank cap. I let a load of air out the radiator and the coolant level in the expansion tank dropped back to normal. I immediately repeated the test and got exactly the same results; another load of air in the radiator and coolant leaking out of the expansion tank cap. Bubbles were visible periodically rising in the expansion tank.
At no point did the coolant temp rise above "normal" readings, and driving "normally" for road use the problem does not manifest, it only happens under hard use.
I'm not sure what to do next. The vehicle has a mechanical and electrical water pump. The electric pump is working, and I assume the mechanical one is as well. The fan is operating normally. My gut is saying it's a head gasket issue causing the coolant system to pressurise, but the lack of gas detection on the sniffer test goes against this. However, the sniffer test has not been carried out after "hard" use. Is it possible a dodgy head gasket can only leak combustion gases under hard use and not "normal" use? I'm wondering whether to change the thermostat, but I don't see how that would cause air to forum in the top of the radiator?
Any help or advice welcome, got some charity days coming up soon so need to get this resolved!
Cheers
SteveSlowboy said:
As a first stab I would try replacing the radiator cap - perhaps it's not holding the pressure required?
There isn't a radiator cap, just a bleed bolt on top of radiator. However, I have replaced the expansion tank cap (as stated above) but the coolant is still being forced out past it. Cheers
Cheers for all the replies, much appreciated.
To answer some of the questions:
The expansion tank holds, at a rough guess, around 1 litre. Unlike most normal systems, there isn't a return feed to it. There is one connection, a hose attached to the bottom which must feed into the coolant system. The system doesn't appear to have any "self bleed" mechanism that I can tell. There is a single outlet/inlet connection at the top of the expansion tank but this is capped/blocked off. I checked with the factory and this is correct.
The radiator is vertical at the front, and I am not loosing coolant from anywhere other than via the expansion tank cap (which I have replaced) when the engine is driven hard.
I am measuring the coolant temp via the dash display, and also via the OBD port using a Bluetooth dongle and a tablet (there is approx 4 degrees difference between the two, one sensor for the dash and one for the ECU).
I will investigate further and try some of the suggestions and report back.
Thanks again
To answer some of the questions:
The expansion tank holds, at a rough guess, around 1 litre. Unlike most normal systems, there isn't a return feed to it. There is one connection, a hose attached to the bottom which must feed into the coolant system. The system doesn't appear to have any "self bleed" mechanism that I can tell. There is a single outlet/inlet connection at the top of the expansion tank but this is capped/blocked off. I checked with the factory and this is correct.
The radiator is vertical at the front, and I am not loosing coolant from anywhere other than via the expansion tank cap (which I have replaced) when the engine is driven hard.
I am measuring the coolant temp via the dash display, and also via the OBD port using a Bluetooth dongle and a tablet (there is approx 4 degrees difference between the two, one sensor for the dash and one for the ECU).
I will investigate further and try some of the suggestions and report back.
Thanks again
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff