BGP21 here with another mystery (to me, anyway) for your mulling pleasure...

The Background:
I just completed a multiple-months-long coolant system overhaul (among other supercharger/intake/ignition repairs), including installing a new water pump, upgraded coolant pipes, new coil packs, spark plugs, intake gaskets, new S/C coupler & snout, not to mention my blood/sweat/tears shed along the way.

The Mystery:
In the normal transmission Drive mode, the car drives great, sounds great, no issues to report. I've taken it out on 15-20 mile stints on three separate occasions and it feels better than it ever has in most ways. It doesn't overheat, coolant doesn't leak. BUT... if I put the transmission into Sport Mode, within a mile or two, coolant will come out of the reservoir cap. Not enough to drain the reservoir, but enough to drain it well below the minimal line. Then the engine temp will start to spike very quickly. Yes, of course not enough coolant will cause a car engine to overheat, but the dramatic spike in heat related to the amount of coolant loss seems extreme.

The Troubleshooting:
I have tested the coolant balance (water to coolant percentage), and it is where it should be. I've tested the pressure in the system and have found no leaks. Also, the coolant level in the reservoir doesn't fall, even if the car sits for 48+ hours. I have ordered a new reservoir cap to see if that might be the issue. I suspect that it will not be, since I didn't have an issue with it before all of the fixes. I'm open to the option that anything is possible, though.

Is there anything that is happening from a mechanical perspective, when the transmission is put into Sport Mode vs. Normal Drive Mode, which I should be troubleshooting? Could it be something with the radiators in the S/C, and they don't really come into play until the car is working harder, so it's only happening in Sport Mode? Air pockets in the system that only come into play when the water pump is circulating coolant more aggressively? Should I be exploring some other channels for potential issues? It feels so tied to the Sport Mode because of how quickly it happens.

Thanks for your time. (Also, Happy New Year, everyone!)

 

I'm not an expert on the subject, but it seems odd that sport mode or any changes in the shift pattern on keeping the revs up longer should have an affect on coolant pressure. I've never seen pressure rise to the pointe (on my car at least) where coolant actually comes out of the pressure cap. The only thing that usually affects the coolant pressure drastically is a head gasket issue, which I'm sure you've eliminated. Please keep us posted. I'm quite interested myself with what is going on with your car as this is a first for me. Sorry, I couldn't be more helpful. PS...How many miles on your car?

 

I appreciate your thoughts. I also don't know why Sport Mode would come into play either, it's just that the dots seem to be connecting on a consistent basis. It's very odd.

To answer your question, the Gray Ghost only has 65,000 miles on it and has spent most of it's life being taken care of from what I can tell (no rust, interior in almost perfect condition, coolant Y pipe was replaced with metal option previously, paint in good shape, etc.)

 

Sport mode adds load, load adds heat, heat adds pressure. You may have air trapped in the supercharger. How did you fill the system? Our cooling systems are best vacuum filled. if there’s air trapped in the supercharger intercooler cores, that’s the spot where the heat is most intense under boost. If it were my car, I would stop driving in sport mode, rent or buy a vacuum coolant filler, perform the vacuum fill procedure. Then slowly ease back into your sport mode habits.

 

Do you have the capability to read trans temp. Certain scanners can do it. The reason i ask is because sport mode changes the trans shift points and holds the gear longer for more use of power and thus engages the supercharger more often and raises trans temps because the lockup clutch on the convertor also engages earlier. I would double check that the supercharger intercooler pump is working also. An easy way is to feel the charge coolers on the engine. If working properly they should be warm and not scalding hot like a radiator hose. After a drive. The supercharger coolant pump is always on when the car is running. Another thing is when coolant is cold take out the supercharger cooling system fill plug and check to see if coolant is at the top. I am leaning towards an air lock myself

 

Considering you have just completed a cooling system service, I agree that an air pocket could be a culprit. Vacuum fill and/or proper bleeding should resolve any lingering air pockets.

 

Its a pain to manually bleed the system without a vacuum bleed but it can be done
Ive experienced the same issues as you.
Just keep topping it up and bleeding it about 3-5 times and the air will come out.
or use a coolant fill funnel that connects to the reservoir. Still needs multiple bleeds.

 

bgpenguin21, I had a coolant issue and took the option of changing to a racing coolant that comes without pressure in the system. I'm happy with it, and the experience provoked an idea. By using 100% coolant and not the mix, don't you eliminate the factor of pressure in the system? With your burping of the coolant system, this may react better for you. All for a few dollars more and its the water that makes the steam and pressure. ...

 

Thanks for the feedback everyone. I agree with many replies that air in the system makes the most sense.

For filling the system, I did use a funnel with an extension pipe to raise the funnel high above the level of the top of the SC. Maybe it's time to invest in a vacuum filling solution though.

I will be working on getting any extra air that might be trapped in the system, this weekend. I will update then.

Cheers!

 

UPDATE: I worked to get any lingering air out of the system this weekend. I tried burping the system via the large radiator hose and also removed the expansion tank overflow hose (where it attaches to the upper Y-pipe) again until I saw coolant come out the little hole there.

Took the GG out for a long test drive (30+ mins). Coolant temps looked great the whole time (never touched 90 degrees C). No obvious leaks. Cool.

1/2 mile before my home I gave it the beans in a passing zone. 5,000RPMs in normal drive mode for about 4 seconds. Almost immediately, there's a misting of coolant hitting my windshield on the driver's (LHD) side. Not cool.

It was the lightest misting so I went straight to my garage to visually troubleshoot while the engine was idling. Discovered that the misting was from coolant that was coming out of the hood vent (with the word 'Supercharged') on the left side and then being blown onto the windshield. Anyway, I quickly popped the hood to check where it was coming from and already the leak was nowhere to be seen. Yes, there was some coolant on some of the parts on the front of the engine, but no active leaks that I could see and certainly nothing that would cause a spray of coolant to get out through the hood vent.

I'm thinking that what makes the most sense with regards to the spray effect is that coolant is getting on one of the belts and then being thrown out the vent opening. But I took out my my little bendy camera and did not see any coolant on the belts though. Most of the pooling coolant can be seen near the top of the thermostat housing, on that lip where the hard plastic of the housing meets the upper hose, so I suspect that the leak is at that point or higher.

It's just so odd that the leak can come on so quickly once more than average pressure is applied, but also go away so quickly after just maybe 200 yards of 2,500RPMs. When I check the coolant level in the reservoir when it's cool again (like I did this morning), the smallest amount of coolant is missing. Not even the difference between the High and Low markers on the expansion tank. Could I have the smallest pin-hole leak in history? Enough to create misting, but not enough to invite a blow-out? Should I call Guinness? Grrr...

Note: The thermostat assembly is one of the parts that I recently replaced. It was brand new and OEM and not a cheap knock-off. Is it worth exploring that there might just be a manufacturing defect in that brand new assembly? Has anyone else experienced this before?

I'm interested in anyone's additional thoughts, similar experiences or suggestions for troubleshooting steps to take next. Thanks!

 

Yes.same as before but now you know you have a leak. Rent a pressure tester from an auto parts store. They refund your rental fee when you return it. Then once you find and fix the leak, vacuum fill the system. Remove the under scuttle while you leak check. PIA I know but sometimes the best view is under the car.

 

Thanks @Sean W. That makes perfect sense. That will be my next step. Appreciate the reply. Cheers.