No it doesn't have to be open, helps but not necessary
you can usually borrow a pressure tester and compression tester from your local auto-parts store by leaving a deposit. the same is sometimes possible for the co2 tester, you just have to buy the chemical.
if you can not loan them, then HF is probably the cheapest place to go.

 

The head gasket can blow in different ways. It can just eject exhaust, it can mix coolant in the oil/cylinder, it can allow gas/pressure to migrate between cylinders, or it can allow oil and/or coolant to the outside of the engine. I think I've had most of those issues on different rover engines.... Anyway, when I had a COOLANT leak, it was plainly obvious because the coolant was low and the oil was thin/watery, and the expansion tank was "boiling" with exhaust gas being pushed through the system.

But I have been lucky because most of these symptoms, if not all, can also be cause by a cracked block. The crack can happen at a bolt, or behind a liner, or probably other places, too. A cracked aluminum block is no fun, so I've always bet on the head gaskets, which are... fun? No, they aren't fun, either, but they are much cheaper.

I thought the thermostat had to be open to test pressure at the tank but Dro has more experience than me, so his message is probably right. I also know you can get a chemical that you put in the expansion tank and its color will show the presence or absence of hydrocarbons. I am guessing that the pressure tester is a cap or plug for the expansion tank.

 

As soon as the dash needle moves from center that's considered too hot. Hence the need for monitoring the real temps.

 

Well, I did a bit more playing around with it today and discovered I could get the temp sensing to work. Pocketlogger to the rescue! Also, I reset MIL and P2172 is the only one that came back.

I have no idea if that is valid or not. This website (http://www.autotechscantools.co.za/....000071697.html) says it is P2172
Throttle Actuator Control System - Sudden High Airflow Detected

I saw a forum post for a Dodge SRT that had a guy get the issue with his MAF wiring harness that threw this code.

 

DiscoMike told me that the MAF can cause all sorts of crazy codes, and he was right. I ignored that advice (because my MAF was new) and threw parts at it until I called him a second time... I HAD REPLACED THE HEAD GASKETS AND STILL HAD MISFIRES... he said the same thing and I borrowed a friend's MAF (from his Disco II)... instant success. I didn't have that code but I was having a ton of other, rough idle, misfires... all because of the MAF.
DiscoMike, per usual, was right.

FWIW I bought the cheapo MAF on amazon it is has been doing fine for two years. But if you know anyone with a Disco II, borrow their MAF; you will know immediately whether that is the issue.

As for the MAF wiring harness, it is pretty basic looking at the MAF end. You might try taking the plug apart and spraying electronics cleaner in it. But unless you have been digging around in the bay and put force on the wiring, I doubt it is the wiring. I have been pretty rough with mine (put my food on the wire when I lost balance, pulled the plug loose from the wiring when my gloves slipped, cleaned the connector with BRAKE CLEANER when i didn't have my reading glasses on) and never had a problem.

I've actually never heard of that code before you posted it. Maybe someone else has gotten it before...

 

A particularly heavy sandwich.?

If the forum search is to be believed that's the first time that code has ever been posted.

 

Hahahahha Hahaha. That's funny!

FOOT. NOT FOOD. No food in the engine bay. What a typo!

 

I'm borrowing a pressure tester from O'Reilly auto parts. The adapter seems to screw right on the coolant expansion bottle, but I can't get it to pressurize. One reason is the overflow tube seems to be open, so the air goes right out of it. Does the adapter need to go down into the neck where the two o-rings are on the coolant tank cap? Because the Mityvac tester adaptor I found online isn't really better. ( ) As you can see, its doesn't go down into the neck, so wouldn't all of the air just rush out the overflow also? https://i.imgur.com/Bgr9Sw7.jpg https://i.imgur.com/TAsVSIi.jpg

 

Yes the adaptor has to go deep enough to block off pressure going out the vent. I have read that autozone does not have the correct adaptor either. the HF tester does have the correct cap.

 

HF? What is HF? It looks like the mityvac kit could work with MVA113. Anyway. I ran the truck again today with the pocketlogger attached, so I could monitor temperature.

I found the leak, or at least one. It is the head gasket, external to the head on the passenger side (US) head. I could coolant bubbling out. So the head gasket/gakets are definitely screwed. The other one might have been leaking by the serial number / compression ration stamp, but I couldn't say for sure.

The weird thing is, the system still seems to hold pressure. After you turn it off, when you remove the expansion tank cap there is hissing like it is releasing pressure. (unless that was vacuum)

Before I ran it today, I bled the system per the RAVE. It didn't seem to lose water from the expansion tank, but its hard to be certain. At least not like last time where the tank went pretty much empty. It still overheats, the temperature slowly increased to 200, I dropped the car in gear and it went to 212, then I stopped and it showed 221 and I turned it off immediately.

Could the head gasket alone leaking cause it to overheat? Besides the pressure test, which I will have to attempt later, what should my next step in diagnosing be?

EDIT: sorry for the wall of text, this forum ate all of my paragraph breaks.