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MP7 building pressure in cooling system


steeler
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2009 mp7, what are you guys seeing as the most likely culprit for building pressure in the cooling system? This one is building quickly, literally spraying out of the overflow cap.

I know I'm probably looking at either head/gasket, injector cup or air compressor. Trying to decide which row to take here.

 

 

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No sir. Trying to finish up a couple other projects first.

Still trying to decide where to start. Pulling out cups? Pulling head? I checked the buildup of pressure with the air compressor pumping, and with it kicked out and there was no change, so I think I can rule that out.

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10 hours ago, fjh said:

Easier  stuff first rad cap ,  egr cooler !  Is it throwing up any  codes?

No codes. What I do with these is put a pressure tester on the coolant tank, fire it up and watch to see if the pressure builds. This one instantly started climbing, normally I don't see much pressure building until the coolant temp starts to come up.

At an idle the pressure steadily climbed to 10 psi in about 3 minutes. If I ran the rpms up it would build pressure even faster.

I've only seen this on an mp7 one other time which ended up being pitting in the head where the injector cup seats, letting compression into the cooling system. 

As far as the egr cooler, am I correct that there wouldn't even be 10 psi of pressure there at an idle? I know that it isn't leaking coolant anyway.

 

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I have a thought ! Do it in order of ease if there is such a thing specialy if its an MR !  Remove the turbo hose to the after cooler so it will not build boost at all! run the engine( N/A ) See if this condition persists! This would nail it down to the head area ! then proceed to your cup theory then move on to the head gasket theory if the cups don't show up anything !    just a thought!

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  • 1 month later...

Well, I ended up pulling the cups, didn't see anything so went on and pulled the head, sent it out to be checked. It all checked ok.

Put it back together, same problem! Turns out you can't eliminate the air compressor the way I've always done with older (real) macks. I removed the main air line from the compressor and problem goes away. Shoot air into the compressor at main air line and have bubbles in the coolant tank 

Air compressor replacement time, yay!

 

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18 hours ago, steeler said:

Well, I ended up pulling the cups, didn't see anything so went on and pulled the head, sent it out to be checked. It all checked ok.

Put it back together, same problem! Turns out you can't eliminate the air compressor the way I've always done with older (real) macks. I removed the main air line from the compressor and problem goes away. Shoot air into the compressor at main air line and have bubbles in the coolant tank 

Air compressor replacement time, yay!

 

Too bad we had to go this far to find that compressor is almost harder to do than the EGR cooler O well At least you found it!

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I had to change the compressor on the mp7 at work it was in a frontloader took me over half the morning very tight area to work in. The compressor would pump just fine for a given time then just wouldn't pump I tried to get the valve kits but I was told not available pretty expensive pump on exchange. That sob would pump and then quit and would start pumping again about as bad as when a starter gets a bad spot in it and once a month it wont spin the engine but by the time I show up I turn the key and off it starts. 

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Yes those compressors suck balls! 

Went ahead and did the egr cooler while the head was off, it was pretty clogged.

She's all fixed now. I hate that I pulled a damn head for an air compressor problem. Damn. Oh well I know for the next one.

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  • 11 months later...

Had the same situation today. Checked a customers truck that was blowing out coolant.   His compressor was weak Building pressure also. First I used shop air to fill tanks from the governor fitting and got full pressure on dash gauges.  Then pulled tank plugs all out and let run. No problem with coolsnt

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