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Doubled

So I’ve never even laid eyes on an 870 but something in the previous posts didn’t quite add up. I found a diagram on quickserve of an 870 EGR circuit. It’s the same as an 871 so why wouldn’t you use a bypass tube after removing the cooler?

(03-09-2023 )schISM Wrote: [ -> ]So I’ve never even laid eyes on an 870 but something in the previous posts didn’t quite add up. I found a diagram on quickserve of an 870 EGR circuit. It’s the same as an 871 so why wouldn’t you use a bypass tube after removing the cooler?

This diagram is wrong for the CM870, The EGR valve is attached directly to the exhaust manifold before the cooler.

(03-09-2023 )marek4792 Wrote: [ -> ]

(03-09-2023 )schISM Wrote: [ -> ]So I’ve never even laid eyes on an 870 but something in the previous posts didn’t quite add up. I found a diagram on quickserve of an 870 EGR circuit. It’s the same as an 871 so why wouldn’t you use a bypass tube after removing the cooler?

This diagram is wrong for the CM870, The EGR valve is attached directly to the exhaust manifold before the cooler.

Hmmm, esn# 79153300, CPL#8518 2006 CM870. Does anyone have a proper diagram of the cooler structure mentioned above?

(03-09-2023 )schISM Wrote: [ -> ]Hmmm, esn# 79153300, CPL#8518 2006 CM870. Does anyone have a proper diagram of the cooler structure mentioned above?

looks like this. #12 goes to the block up front and #22 goes from the egr cooler to the thermostat housing.
[attachment=8822]

Ok, just found some pics on ebay. Now I understand, that is one sorry looking design both for valve placement and heat dissipation to the water jacket. How those tiny lines could flow enough to cool the egr gasses is beyond me.

(03-09-2023 )marek4792 Wrote: [ -> ]

(03-09-2023 )schISM Wrote: [ -> ]Hmmm, esn# 79153300, CPL#8518 2006 CM870. Does anyone have a proper diagram of the cooler structure mentioned above?

looks like this. #12 goes to the block up front and #22 goes from the egr cooler to the thermostat housing.

Thanks marek, a pic is worth a thousand words!

also the passages for coolant flow into the head at each cylinder in the head gasket for the CM870 are larger as well.

regardless... a lot of thermo testing has been done and indeed the CM871's run hotter on #5 and especially #6 if there is no coolant flow to the back of the block via the egr cooler circuit with it plated off.

Also, the CM871 and newer water pump suffers 70+ PSI of head pressure on the now, dead circuit at the back of the pump for that port, if someone plates it off because they removed the egr cooler. This face-loads the bearings and shortens the life of the water pump as well.


The coolant flow is more balanced in the 871's and newer engines overall too ... and yes, CM870's do run actually run slightly hotter on #5 and #6 as well ... even from factory.. but it is not as bad though with them due to larger passageways in the head gasket and more flow thru the older style of water pump.


also.. on all newer-designed 15-litre QSX and non-egr engines that do not have an egr cooler installed, they have in place, a factory bypass for just this reason.

here is a reference to this...
http://rawze.com/forums/uploads/201908/p...1e0970.pdf

Replaced the coolant reservoir today because it was starting to leak. Once I finished installing it I got the truck up to 182 degrees and it wasn’t puking coolant.Here’s a video of it https://imgur.com/a/YB8voDd