I picked up a 2002 fullsize XLS with 3.5 L, 180,000 miles. Owner said it had a bad head gasket and had minorly overheated once or twice as he drove it home. I confirmed there is water in the oil, and some missing radiator coolant. He installed a new radiator but that didn't fix overheat problem.

It wouldn't crank for 3 days and then yesterday it started up. Very rough and seems to be placing a lot of unburnt fuel out tailpipe. Not smoking very badly at all, just sounds and smells very fuel rich. Very little faint white smoke, which I hope means the head gasket break is very small.

Ran the code reader and it shows P0300, Multiple Cylinder Misfires Present.

My friend thinks a bad fuel injector may have blown the head gasket. Is that true? If so, I want to check them all over.

Do these injectors commonly fail and cause damage to themselves?

Has anyone has success at checking and bench cleaning the injectors like the YouTube videos describe?

After I check injectors I plan on changing motor oil/filter with 15w-40. Then draining, flushing and backflushing radiator and heater core. And finally adding a bottle of Steel Seal to see if I can solve head gasket leak that way, without pulling heads off.

Any suggestions on what to check other than injectors, for the bad head gasket cause? I don't want to repair it just to have it break again if I can avoid that. Thank you!

A bad fuel injector will not cause a head gasket to blow. Injectors on Monteros are not known to fail - it's far more likely that you've got fouled plugs that are misfiring and allowing unburned fuel out the exhaust. I wouldn't be running the engine much as unburned fuel will kill your catalytic converter in short order.

Head gasket failures are almost always due to overheating - I'd pressure test the cooling system then plan a thorough overhaul with new thermostat, hoses, radiator cap, etc. Use OEM Mitsubishi thermostat and radiator cap - the Stant garbage at your local parts store is worthless. What kind of radiator did the previous owner install? A cheap plastic eBay radiator is almost as worthless as a Stant thermostat.

Steel Seal is worth trying - beats having to replace the head gasket.

I've had great luck with Steel Seal. I say a leak down test, a compression check will tell you a loud about that motor.

One observation wrt thermostats...

Put them in a pot of water with the thermometer and see at what temperature they open. Failure rate (not opening at listed temperature) is high. I don't find Stant to be any worse than OEM. What I have noted is a shift to Made in China which I find a higher failure rate.

Recently replaced thermostat. My new one opened at 200 degrees. I need 190. As it was late, I dug out my spare from my emergency kit that had been there for more than 15 years. 190 degree. Both were Stant. One Made in USA, the other made in China.

Key take away, don't trust the listed temp. Always test it....

I totally agree. OEM or Stant not reliable, even "OEM" might be made by Stant.
I used to trust Stant. Most people don't know as they only have faux gauges. I'd also say opening before spec'd temperature is as common.

Compression checking cooling system sounds like a good idea. I think before I remove heads I'll compression and leak down tests the V6.

It seems to be flooding so quickly and badly I can smell unburnt fumes from motor area and tailgate. There isn't any pooling or tank loss I can see. After it sits for 48+ hours or more it will start when I hold pedal to floor. Tonight it started twice, and was only ran for about 8 minutes total. Would not start up on 3rd try when I was going to test transmission in parking lot.

I think the previous owner had it when this Montero started having problems and somehow it has led to it dumping excess fuel into the system. My guess is an injector is either stuck open or on, or like someone else said, something controlling/feeding ECU or injectors emissions info is causing the injector(s) to flood the engine.

But the only diagnostic code I have is the P0300 "random multiple cylinder misfires". Which is common to blown head gasket also, which it seems to have based on water in the oil. So I guess I'll pull the injectors (while I'm getting to everything else), and plugs/coils of course, test what I can, and then DIY clean them with process I saw on YouTube using a battery and spray can carb cleaner. Replace o-rings and screens if I can find kit.

Looking to source a rebuild kit for the injectors. If anyone has used one from a supplier and been happy with quality and price.

Anyone used a good repaie manual for 2002 year?

Do an oil change, the fuel is diluting the oil and your bearings will be toast if you're not careful.



I send mine to Witchhunter.com. For $22 per injector they'll test, clean, fix, re-test with report, and you'll get new seals. Turnaround about 1 week.