robertmee
02-21-2018, 01:37 PM
I've been fighting coolant issues for a few months now. I've replaced the thermostat and the reservoir cap. Still the issue persists. What's weird is I can go a month and all is fine, then suddenly, overheat. I do the full FastBlackMerc burp each time on an incline in my driveway, so it's not a matter of burping. What I noticed last time, is that coolant was constantly leaking from the top of the reservoir under the cap. I thought it was a bad cap, so I swapped caps with the overflow tank, but it didn't help. So I bought a new cap, and that seemed to solve it for over a month. Until today, when I parked, the car was not overheating, but I saw coolant under my car when I came out of the gas station. Was hoping it was someone else's, so I drove a couple of miles to my destination and then popped the hood to check. Sure enough, coolant was again flowing from underneath the reservoir cap. It wasn't boiling, and the dash gauge still showed under 1/2. My Aerometer showed 206 degrees.
I assumed I could limp home, but after about 10 miles, it started to climb. The Aerometer gauge reached 218. I pulled over, let it cool, filled up the reservoir, opened the crossover and burped it best I could and made it home with the dash gauge never going above half. Aerometer again showed around 208 degrees.
So, a couple of questions.
1) Is the cap ever supposed to let liquid out? I thought it vented steam, but the liquid was supposed to go the small overflow tank. Could it be the threads on the fill hole of the reservoir are allowing air in? They don't look munged, but maybe?
2) Is the cap supposed to be able to twist on indefinitely? My OEM cap, would start clicking and you could turn it forever in the tighten direction. My new aftermarket cap, initially didn't do that. But during this hot overflow condition, I found I could also turn it forever...it would seem to get loose, then tight, then too far, loose again.
3) Is there something more insidious going on? This is a trilogy setup, and the engine is now forged and has about 20K on it. I've never let it overheat, and up until this sporadic overheating, it's run like a champ.
I assumed I could limp home, but after about 10 miles, it started to climb. The Aerometer gauge reached 218. I pulled over, let it cool, filled up the reservoir, opened the crossover and burped it best I could and made it home with the dash gauge never going above half. Aerometer again showed around 208 degrees.
So, a couple of questions.
1) Is the cap ever supposed to let liquid out? I thought it vented steam, but the liquid was supposed to go the small overflow tank. Could it be the threads on the fill hole of the reservoir are allowing air in? They don't look munged, but maybe?
2) Is the cap supposed to be able to twist on indefinitely? My OEM cap, would start clicking and you could turn it forever in the tighten direction. My new aftermarket cap, initially didn't do that. But during this hot overflow condition, I found I could also turn it forever...it would seem to get loose, then tight, then too far, loose again.
3) Is there something more insidious going on? This is a trilogy setup, and the engine is now forged and has about 20K on it. I've never let it overheat, and up until this sporadic overheating, it's run like a champ.