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Hey guys,Im having a bit of a issue with a 2004 CX 613 Mack tractor. A month ago after a 150 mile trip up to Albany NY, the expansion tank in the truck filled up with coolant and built up pressure like it was going to burst. I shut it down and cracked open the line on the upper radiator hose to relieve the pressure. Once I did that I was able to hear the coolant start flowing through the engine again and I drained out the expansion tank. I refilled the upper tank and kept a eye on it the ride back. The truck never overheated or ran hot the entire time this happened but it just pressurized the expansion tank.

When I got back to the shop I installed 2 new thermostats and found that the radiator cap wouldn't hold pressure so I replaced that too. I have no oil in the coolant, no coolant in the oil, no white smoke, no bubbles in the coolant, no exhaust smell from the coolant, no coolant consumption,and nothing that would point towards head gasket. I also checked the air tanks to be sure the compressor wasn't at fault.

I drove the truck hard all around the neighborhood and lugged it down as much as I could but I couldn't replicate the problem so I figured it was fixed. That was until I took the truck out on a short haul into NJ and had the same issue within the first 40 miles of the trip. Now here's what I noticed. If I baby the truck and keep it running at 1/2 throttle with no load, the temp and the coolant will be normal and not build pressure. If I keep it at full throttle with a load on, it will build up pressure and start blowing out the expansion tank. On some extended drives at full throttle with the cruise control on, I would get the electronic malfunction light on the dash and I would loose all turbo boost for a few seconds then it would clear and the truck would pull like normal. Lately it hasn't been doing that but started building this pressure under a load. I been reading about the EGR coolers failing so I'm wondering if this would sound like something related to that problem or am I looking at something more serious?

Within the last 2 yrs,the oil cooler filter was replaced. The water pump was replaced 3 months ago due to it leaking out the weep hole along with the water filter and a full coolant flush was done.

Thanks for any info.

Edited by Astoria Mechanic
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Hey guys,Im having a bit of a issue with a 2004 CX 613 Mack tractor. A month ago after a 150 mile trip up to Albany NY, the expansion tank in the truck filled up with coolant and built up pressure like it was going to burst. I shut it down and cracked open the line on the upper radiator hose to relieve the pressure. Once I did that I was able to hear the coolant start flowing through the engine again and I drained out the expansion tank. I refilled the upper tank and kept a eye on it the ride back. The truck never overheated or ran hot the entire time this happened but it just pressurized the expansion tank.

When I got back to the shop I installed 2 new thermostats and found that the radiator cap wouldn't hold pressure so I replaced that too. I have no oil in the coolant, no coolant in the oil, no white smoke, no bubbles in the coolant, no exhaust smell from the coolant, no coolant consumption,and nothing that would point towards head gasket. I also checked the air tanks to be sure the compressor wasn't at fault.

I drove the truck hard all around the neighborhood and lugged it down as much as I could but I couldn't replicate the problem so I figured it was fixed. That was until I took the truck out on a short haul into NJ and had the same issue within the first 40 miles of the trip. Now here's what I noticed. If I baby the truck and keep it running at 1/2 throttle with no load, the temp and the coolant will be normal and not build pressure. If I keep it at full throttle with a load on, it will build up pressure and start blowing out the expansion tank. On some extended drives at full throttle with the cruise control on, I would get the electronic malfunction light on the dash and I would loose all turbo boost for a few seconds then it would clear and the truck would pull like normal. Lately it hasn't been doing that but started building this pressure under a load. I been reading about the EGR coolers failing so I'm wondering if this would sound like something related to that problem or am I looking at something more serious?

Within the last 2 yrs,the oil cooler filter was replaced. The water pump was replaced 3 months ago due to it leaking out the weep hole along with the water filter and a full coolant flush was done.

Thanks for any info.

Check the screen in the lower radiator pipe leading to the oil cooler.

"Mebbe I'm too ugly and stupid to give up!"

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Hey guys,Im having a bit of a issue with a 2004 CX 613 Mack tractor. A month ago after a 150 mile trip up to Albany NY, the expansion tank in the truck filled up with coolant and built up pressure like it was going to burst. I shut it down and cracked open the line on the upper radiator hose to relieve the pressure. Once I did that I was able to hear the coolant start flowing through the engine again and I drained out the expansion tank. I refilled the upper tank and kept a eye on it the ride back. The truck never overheated or ran hot the entire time this happened but it just pressurized the expansion tank.

When I got back to the shop I installed 2 new thermostats and found that the radiator cap wouldn't hold pressure so I replaced that too. I have no oil in the coolant, no coolant in the oil, no white smoke, no bubbles in the coolant, no exhaust smell from the coolant, no coolant consumption,and nothing that would point towards head gasket. I also checked the air tanks to be sure the compressor wasn't at fault.

I drove the truck hard all around the neighborhood and lugged it down as much as I could but I couldn't replicate the problem so I figured it was fixed. That was until I took the truck out on a short haul into NJ and had the same issue within the first 40 miles of the trip. Now here's what I noticed. If I baby the truck and keep it running at 1/2 throttle with no load, the temp and the coolant will be normal and not build pressure. If I keep it at full throttle with a load on, it will build up pressure and start blowing out the expansion tank. On some extended drives at full throttle with the cruise control on, I would get the electronic malfunction light on the dash and I would loose all turbo boost for a few seconds then it would clear and the truck would pull like normal. Lately it hasn't been doing that but started building this pressure under a load. I been reading about the EGR coolers failing so I'm wondering if this would sound like something related to that problem or am I looking at something more serious?

Within the last 2 yrs,the oil cooler filter was replaced. The water pump was replaced 3 months ago due to it leaking out the weep hole along with the water filter and a full coolant flush was done.

Thanks for any info.

That flush that was done might have broke loose some scale in the block and now its clogged the oil cooler inlet screen and now overheated the EGR cooler and cracked it causing coolant push. I would first pull out that oil cooler inlet screen in the "Y" pipe that connects the lower radiator piping the the oil cooler. Rasler probably has that Mack service bulletin and can post it as I dont have it on this computer. Hopefully it didnt crack the EGR cooler. Its easy to change a EGR cooler but $$$$$

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Thanks for the replies! We purchased the truck from a Mack dealer in 06 and I'm pretty sure they performed the thermostat housing updates. I will still go over the details in the file and make sure. That one update from 2008 may have come back and caused the issue. We have 3 identical trucks all purchased at the same time and only my truck is having the problem.

Thanks for the info! Ill post up when I start going through it either tonight or tomorrow.

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Today I put a lot of effort in the truck. I checked the oil cooler filter and it was clean, I pulled the steel tube off the oil cooler to the EGR, it was dry and had only carbon inside, I pulled the radiator hoses off and flushed it out. It was also clean and had no restrictions. I checked the oil in the trans and it was clean. I put a new water filter on it and checked the anti-freeze I drained out and that was clean. I pressure tested it and its holding full pressure without dropping. I also pulled out the water pump to make sure the impeller wasn't slipping on the shaft. That was tight and fine too.

How long before I set this thing on fire? :rolleyes:

Edited by Astoria Mechanic
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Here are a couple of things you might check. If you have a two piece reservoir arrangement replace it with the one piece metal tank. If the cooling system is not updated with the parts in the bulletin I would install them. The water pump cartridge may be sucking air or the water pump housing (big aluminum housing that the cartridge is bolted into) may be cavitated, this will cause your problem. Measure the OD of the pulley on the water pump cartridge. The AC cartridge has a 5 1/4" pulley, the AI uses a 5 7/8" pulley. Installing the AI pump cartridge will cause 10% higher coolant temperatures.

"Mebbe I'm too ugly and stupid to give up!"

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Here are a couple of things you might check. If you have a two piece reservoir arrangement replace it with the one piece metal tank. If the cooling system is not updated with the parts in the bulletin I would install them. The water pump cartridge may be sucking air or the water pump housing (big aluminum housing that the cartridge is bolted into) may be cavitated, this will cause your problem. Measure the OD of the pulley on the water pump cartridge. The AC cartridge has a 5 1/4" pulley, the AI uses a 5 7/8" pulley. Installing the AI pump cartridge will cause 10% higher coolant temperatures.

Thanks for the tips. Just what does AC and AI stand for? The truck has close to 300K miles on it, I just find it strange that these problems would happen all of a sudden. The water pump theory sounds on par with whats going on. I'm wondering if the dealer sent us the wrong pump and that is the issue. It seems that this pumping pressure into the expansion tank seemed to happen after the waterpump install. Today when I had it out I checked the backplate that the impeller of the waterpump spins against and it was clean and had no marks on it.

I will get a measurement on that pulley. I can see how a smaller pulley will turn faster and cause cavitation inside the housing under higher RPM.

Edited by Astoria Mechanic
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Thanks for the tips. Just what does AC and AI stand for? The truck has close to 300K miles on it, I just find it strange that these problems would happen all of a sudden. The water pump theory sounds on par with whats going on. I'm wondering if the dealer sent us the wrong pump and that is the issue. It seems that this pumping pressure into the expansion tank seemed to happen after the waterpump install. Today when I had it out I checked the backplate that the impeller of the waterpump spins against and it was clean and had no marks on it.

I will get a measurement on that pulley. I can see how a smaller pulley will turn faster and cause cavitation inside the housing under higher RPM.

AC is ASET cooled EGR, AI/AMI is internal EGR. The ASET engines were designated as either AC (highway usage) or AI/AMI (vocational usage). Both engines have EGR. The AC has a "selective" system that allows the engine ecu to increase and decrease EGR as needed through control of an EGR valve. The AI/AMI on the other hand inducts EGR gas on every stroke due to an extra bump on the cam lobe.

"Mebbe I'm too ugly and stupid to give up!"

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AC is ASET cooled EGR, AI/AMI is internal EGR. The ASET engines were designated as either AC (highway usage) or AI/AMI (vocational usage). Both engines have EGR. The AC has a "selective" system that allows the engine ecu to increase and decrease EGR as needed through control of an EGR valve. The AI/AMI on the other hand inducts EGR gas on every stroke due to an extra bump on the cam lobe.

Thanks for the education on these engines. If it was a mechanical 300 or 350 in a R model, I would have this already figured out. This engine is foreign to me in more ways then just saying Renault on it! Its a day cab tractor, nothing heavy duty, it was originally built to haul a tanker when we bought it which would probably make it fall into the AI usage. I haven't had the EGR apart or even know if it has the "selective" system in it, but we have 2 other identical tractors that I can compare the water pump pulley to if I have a doubt. The more I think about it the more it would make sense that its fine at a lower RPM and would build pressure at a higher RPM if the pump is turning too fast and cavitating in the housing. I have also noticed that the coolant temp is lower then the other two trucks which would also be a indication of it turning faster then it should be. I really appreciate the info. It is something that I would have over looked considering its a brand new pump and I had no idea of 2 different variations of it. I hope to have a answer tomorrow if there is a difference.

Thanks a million!!! :thumb:

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I think I was a little unclear regarding the engines, here's a little more information. A CH, CX, CHN, or CXN chassis with an engine built after 2002 will have an AC engine, easily identified by an external EGR valve on the exhaust manifold and a VGT turbo. A CV, LE, MR, or RB chassis with an engine built after 2002 will have an AI or AMI. These engines have no EGR valve and have a standard turbo. The AI and AMI originally had the same front design (old style water pump) as the earlier E-Tech enignes, but later adopted the same front end (except for LE, possibly MR) sometime around 2004.

I would look into changing the coolant reservoir to the one piece metal tank.

"Mebbe I'm too ugly and stupid to give up!"

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I think I was a little unclear regarding the engines, here's a little more information. A CH, CX, CHN, or CXN chassis with an engine built after 2002 will have an AC engine, easily identified by an external EGR valve on the exhaust manifold and a VGT turbo. A CV, LE, MR, or RB chassis with an engine built after 2002 will have an AI or AMI. These engines have no EGR valve and have a standard turbo. The AI and AMI originally had the same front design (old style water pump) as the earlier E-Tech enignes, but later adopted the same front end (except for LE, possibly MR) sometime around 2004.

I would look into changing the coolant reservoir to the one piece metal tank.

I certainly agree with rhaslers suggestion to change to the one piece metal coolant tank,i went through a similar situation with my 2001 CX,went through 6 plastic replacements before the metal tank was even available as an option!.....it will sure save you a lot of aggravation/greif! since the change i have had 0 problems with the new set-up...................Mark

Mack Truck literate. Computer illiterate.

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I certainly agree with rhaslers suggestion to change to the one piece metal coolant tank,i went through a similar situation with my 2001 CX,went through 6 plastic replacements before the metal tank was even available as an option!.....it will sure save you a lot of aggravation/greif! since the change i have had 0 problems with the new set-up...................Mark

Yeah I think I may look into that. I checked the pulley and its the 5-7/8 one. The one piece metal tank eliminates the expansion tank and makes it a completely closed system? If Im building pressure like that wouldn't that blow the cap off it instead?

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Thanks for the tips. Just what does AC and AI stand for? The truck has close to 300K miles on it, I just find it strange that these problems would happen all of a sudden. The water pump theory sounds on par with whats going on. I'm wondering if the dealer sent us the wrong pump and that is the issue. It seems that this pumping pressure into the expansion tank seemed to happen after the waterpump install. Today when I had it out I checked the backplate that the impeller of the waterpump spins against and it was clean and had no marks on it.

I will get a measurement on that pulley. I can see how a smaller pulley will turn faster and cause cavitation inside the housing under higher RPM.

The AC engine comes in the CX/CH style trucks while the AI/AMI comes in the CV/CT/MR/LE style trucks. Make sure you have a 16 psi radiator cap on there too.

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Yeah I think I may look into that. I checked the pulley and its the 5-7/8 one. The one piece metal tank eliminates the expansion tank and makes it a completely closed system? If Im building pressure like that wouldn't that blow the cap off it instead?

The one piece tank has an overflow fitting soldered into the filler neck.

"Mebbe I'm too ugly and stupid to give up!"

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Yeah I think I may look into that. I checked the pulley and its the 5-7/8 one. The one piece metal tank eliminates the expansion tank and makes it a completely closed system? If Im building pressure like that wouldn't that blow the cap off it instead?

If the pulley is 5 7/8" and it's on an AC engine then it's the wrong pump. Check back and see what part you were sold, the part number for the AC cartridge used to be 316GC3193. I don't know if the number has changed though.

I just checked, same number still.

"Mebbe I'm too ugly and stupid to give up!"

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If the pulley is 5 7/8" and it's on an AC engine then it's the wrong pump. Check back and see what part you were sold, the part number for the AC cartridge used to be 316GC3193. I don't know if the number has changed though.

I just checked, same number still.

I measured it and then measured the pulleys in the other 2 identical tractors and they are all the same size. I think I will follow the advise and go for a one piece metal tank. I appreciate all the responses. Its always better to get advice from guys who have experienced this and found a solution then for me to just throw money and time into the truck and never solve anything.

I shall start my search for a tank tonight!

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Just a update... I ordered the one piece tank from Mack yesterday and today and they sent me the wrong part. The parts guy cross-referenced the tank part number on the TSB and came up with the number of the part he sent me which was just the top half metal tank. Thanks to you guys, I faxed him over the TSB showing the tank and Ill have the right tank on Friday morning. Crazy thing was that the top metal half of the tank at my cost was $370, the one piece metal tank was around $295. You would think half a tank would be cheaper! :rolleyes:

Im just wondering that after running almost 290K miles with the split tank set-up, why would it all of a sudden start to build pressure? Im wondering if higher mileage plays a part in this or just a design flaw that shows its ugly head at any given time?

Ill have it installed on Friday then run the hell out of it and see what it does. Next step after this is to tear it down. :(

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  • 2 weeks later...

Well today was the first day out with the new tank setup. I have 2 runs from the Trade center to NJ and I been pushing it as hard as I can to see if its really fixed, so far so good. The temp gauge has been doing its normal up and down sweeps as well as the oil temp. Nothing blowing out the overflow line and the temp also comes down after idling for a while unlike it did the last time. I would have to really put some long distance miles on it like I did when it was blowing out the last time to really prove its fixed, but so far its back in service.

Thanks for all your help gentlemen with the TSB info. I probably would have ended up tearing this thing down only to have the same issue after all that labor.

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I had the same issue w one of our macs, it drove me nuts, it was the Egr. It had a very small in crack that would only build pressure under loads, once I R/R Egr ran like a champ and never broke down again. Hope this helps, UPS mechanic.

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Check the air compressor.

I had a E7 427 that was puking coolant & overheating, turned out that there was a crack in the air compressor allowing air pressure into the cooling system.

Also, this past week where I work now, we had a Cat c13 in a IH Paystar blowing coolant out so bad it ruptured the reservoir tank. Turned out to be a blown head gasket in the air compressor.

"If You Can't Shift It Smoothly, You Shouldn't Be Driving It"

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