Overheating issues continue - pulling out hair

[robertmee]

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.

[RF Overlord]

Sounds like the threads on the reservoir are fubar. Borrow a pressure tester and pump up the system to 16 pounds and see if it holds.

[fastblackmerc]

Could be the cap or threads on the tank.

[MMBLUE]

Cooling Mod done?
Did you drain entire system?
Have you confirmed water pump working?
Is it a 185 T-stat ?
Did you test the T-stat in boiling water to confirm it is working?

[Comin' in Hot]

Where did you get your thermostat? It’s different from a Crown vic, I would go to the dealer and get a ford thermostat.

[fastblackmerc]

I suggest a 170 degree Reisch Performance thermostat.

[RubberCtyRauder]

any t stat temp other than stock will need to be addressed for in a tune. 170 stat for ex. makes no diff if pcm thinks it has a 195 in it. the pcm controls the fan

[Chayton]

FIRST TIME I WENT TO FLAPS AND ASKED SPECIFICALLY FOR 2003 MERCURY MARAUDER THERMOSTAT I WAS GIVEN A CROWN VIC ONE! MY COOLING PROBLEMS FROM THERE ONLY GOT WORSE. IRONICALLY IT WAS A BAD CAP TO BEGIN WITH. I ENDED UP PUTTING THE ORIGINAL TSTAT BACK IN, AND BEATING THE HE DOUBLE HOCKEY STICK OUT OF THE REPLACEMENT WITH A BFH

[robertmee]

Lol on the BFH. Yeah it's a MM tstat. I'm thinking it might be the tank threads even though they look ok. I noticed when burping yet again today, the cap doesn't go on level...I could put it on at an angle.

But just for my own education should fluid ever pour out of the cap? I've always seen caps release steam and then blow up fluid if opened...but this was a constant river of fluid running out of the cap.

[fastblackmerc]

Sounds like it might be cross threaded. Is the gasket in the cap intact?

[8UWITH6]

Before you waste anymore time throwing parts at this what caused the overheat or temperature issues? Was it out of the blue? While these cars are difficult to bleed the cooling system your intermittent issue has me worried. I would have a shop perform a block test on your car. It checks for the presence of combustion gasses in the cooling system. IE - blown headgasket, cracked head, etc.

[robertmee]

I have a block test kit...no combustion gasses in the fluid. Ordered a new fomoco reservoir and cap. Will update when I install...flu has me down right now.

[Turbov6Bryan]

Dont forget to replace that COT oring. I have plenty here in you guys need some.
2.00 shipped for 2 cot orings

[Spectragod]

#1 problem for mod motors overheating..... bad cap on the tank. From a fleet perspective I see it regularly, it’s not uncommon. If your cap now spins and didn’t before, your caps bad.


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[Svashtar]

Dont forget to replace that COT oring. I have plenty here in you guys need some.

2.00 shipped for 2 cot orings

LOL! Figures. Think I paid $14 online for the pair I got recently. Then realized I should replace the third in the middle as well, and “only” paid $5 for that one.

Should have checked here first.