'00 Durango 5.9l,

I recently did a side job for a friend of a friend that needed immediate repair. With her having 3 kids and being recently unemployed, I agreed to work something out. Anyway, I now have a Durango to wake up from it's 3 year coma.

Apparently, it was parked after overheating. The coolant res. was at the correct fill mark, but the upper hose was bone dry. I filled what I could through the upper hose/ pressure cap. I also changed the oil, which looked sludgy but had no coolant I could see, the oil fill cap had a white sludgy discoloration, not sure if it was just from sitting, or was relative to gasket failure/ head fracture. The engine fired right up but, has a rough idle. I did not feel coolant pressure or heat on the lower rad. hose, heater core lines, or radiator in the time I felt the thermostat should have opened. The Temp Gauge slooooowly climbed up but never got to operation range, I assumed the readings were inaccurate. I shut the engine off and ran a compression test. I pulled cyl#1 first and the spark plug looked carbonized and the rest were looking good.

Compression test: (factor in a 30+yo tester, and /or operator error)
Cyl. #1 slightly above 75 psi, <80psi.
Cyl. 2- 8 between 100psi -105psi
(cold engine)

Still no Fault Codes at this point.
I changed out the water pump, therm. (195), and replaced the spark plugs. The engine still runs rough, also the vibration damper looks to have a wobble. Coolant is now flowing but I also see large bubbles with the cap off (at upper hose), unsure if that is trapped coolant system air or exhaust. The headers Y into a single cat. then dual off. So the slight steam/ fog was equal between pipes and seemed adequate to the 60 degree weather. I had to pick up my kid so I left it at that. So if the verdict is a cracked head, what are the options? I would love to replace both and do a full rebuild, but, my wallet disagrees. What would replacing one head effect?
http://kingcylinderheads.com/Chrysle...ad-K181CG.html

 

With compression low in at least one cylinder and no rocker/lifter noise (at least nothing you've mentioned), the heads probably need to come off. It could be a burned exhaust valve, blown gasket, or a cracked head, if you're pretty sure your compression tester isn't reading accurately.

Normal cylinder pressure should be around 160 (give or take a little). It takes at least 90 PSI to get a cylinder to fire well enough to run. For you to have between 100 and 105 in 7 cylinders....well, again, I hope your guage is just reading low. If that really is the case, then the 75 PSI you read in #1 is probably over 100 PSI, and the miss could be caused by something else.

I've never actually cracked a 360 head, but on most vehicles, when you crack a head from overheating, it's between a couple of valves (usually exhaust) and both cylinders will get the about the same pressure reading.

A burned exhaust valve will usually cause near zero pressure and a dead miss.

A blown head gasket can present in many ways, but what you've described (low pressure in one cylinder, bubbles in radiator, engine miss), this would be my best guess.

My recommendation would be to pull the head off that side and check the valves for damage and the head for cracks and take a really close look at the gasket around #1 cylinder. Unless your head is actually cracked (my guess is that it is not), no need to replace it.

Also....any air trapped in your coolant system is usually forced out the first time the thermostat opens.

P.S.
Buy or borrow another compression tester and verify your readings. If those 7 cylinders are really that low.....well, that's an entirely different story and I'll talk about that if you do another compression test and post the results.

 

+1 on everything above. Use another compression tester to verify the results 'cause they sound low, but at least they're consisitent. Check the harmonic balancer for damage / wear. It'll cause rough running as well.

A cylinder leakdown test will give you some more information on the valve conditions, however if it's that much down on one cylinder it's gonna have to come apart anyways.

Bob

 

For the compression test I pulled the spark plugs off/ replaced individually between each test. Would the compression in the other cylinders lower the readings as well? The engine specified 100psi minimum and 25% difference max, but I reading an article about high/ low compression motors that stated 15 to 20 times the Compression Ratio is the PSI Range. This puts the 160psi mentioned in the range. Compression Ratio 9.1:1 (15)= 136.5,,,,,,,9.1 (20)= 182.... 136 to 182psi, I'll look for a tester and test correctly.

Now that you mentioned a burnt exhaust valve, I did smell fuel rich exhaust. The O2 sensors never picked it up, but I think it was still in the Closed Loop program. I pulled the plug on #1 and the idle never changed, but did with Cyl 3 removed, then popped off the driver side injectors to inspect/ clean, nothing visually alarming and read 13 ohms across them (within specs), replaced still no change. I then pulled the #1 injector wiring connector (to see if the PCM even works), and no idle change, but did for #3. The PCM did display the injector codes. I am waiting on the new cap/ rotor/ wires, but I should've swapped the cables to check for spark.

I am just curious what would happen running the motor with #1 spark plug removed, to see if the air bubbles in the coolant stop?

Well I'll start looking into rebuilding these heads.....

 

Do a dry and wet compression test.

First remove a plug and test and write down your results, then add about 2-3 caps of clean oil down the spark plug hole and re-test and write down the results. Do this on each cylinder and compare findings. If the compression goes up a bunch then the rings are bad, if it stays basically the same then the valves or head gasket is bad.

Now this is not a definitive test, but it does help you figure out what you are going to do.

 

Don't get ahead of yourself, you're not quite to that point yet. One thing I intended to mention before...pull all of the plugs before you do the compression test. You can sometimes get readings that are a little low if the battery isn't up, or if the starter is a little weak. If it's running with just a little miss, is able to pull itself OK and not smoking like a chuckwagon, I find it difficult to believe those compression readings you took the first time were accurate. A motor that has no more squeeze than that will be a real dog, and considering it would almost have to be the rings that are causing the compression to be so low, it would smoke badly.

Like I said before, get another compression tester, pull ALL of the plugs, and use a good battery. When you test each cylinder, turn it over for at least 5 to 7 seconds or more to allow the reading to be as accurate as possible. Once you've done this, you'll have a better idea where you stand. And even if the first readings were close to the truth, there could be other explanations. Timing, for example. A timing chain jumping a tooth or two can easily cause your compression to drop across the board. In fact, I'd think that far more likely than for all the rings to let go at once, without giving you several other indicators. Also, if your compression were that low across the board, the thing would be terribly hard starting.

Once you get another good compression test done, post the results (along with any other info you can think of) and let's take it one step at a time. No need to start thinking you need to rebuild both heads when the solution might be as simple as pulling a head and putting a new gasket in (a pretty easy job).

P.S.
Yes, you can start it with a plug out, but it's not particularly good for it. I've seen bearings turned that way, but that was on a high performance engine, and it was run under a significant load without the plug....still, I wouldn't do it myself.