RAYSTRASH Posted January 3, 2014 Share Posted January 3, 2014 Our 2009 MRU with and MP7, we pressure tested the cooling system and took off the return lines on the fuel tank and fluid (coolant/fuel) was coming out of the return lines. Is this normal, or would it be a sign of bad injector cups? Or could it be something else. Where else should I look? I have new sets of cups and O-rings, but if I don't have to use them, I will send them back. Quote Link to comment https://www.bigmacktrucks.com/topic/34106-2009-mru-w-mp7-coolant-in-fuel/ Share on other sites More sharing options...
Challenger Posted January 4, 2014 Share Posted January 4, 2014 Coolant in the fuel is not normal.Do you have a Davco fuel water seperater? If you do, try bypassing it and recheck. Ive seen bad cups put fuel in the coolant but not coolant in the fuel. This is just what Ive seen, anything is possible. Quote Link to comment https://www.bigmacktrucks.com/topic/34106-2009-mru-w-mp7-coolant-in-fuel/#findComment-224735 Share on other sites More sharing options...
turckster Posted January 4, 2014 Share Posted January 4, 2014 The most likely culprit is going to be the injector cup o-ring(s). It's the one place on the engine that both coolant and fuel are anywhere near each other. You will have to drain the coolant anyway which gives you the opportunity to make sure there is no fuel in the coolant. If there is fuel in the coolant then be prepared to replace coolant o-rings/rubber gaskets in the near future. The fuel will swell the rubber coolant o-rings and gaskets. The first one to usually go is the rectangular o-ring/gasket between the water pump housing and oil cooler cover. When replacing the injector cups, make sure that all old o-ring material is cleaned off the cup bores or this will happen again. Good luck. Quote Link to comment https://www.bigmacktrucks.com/topic/34106-2009-mru-w-mp7-coolant-in-fuel/#findComment-224758 Share on other sites More sharing options...
Challenger Posted January 4, 2014 Share Posted January 4, 2014 The Davco fuel water seperater has coolant flowing through the bottom to heat the fuel. Its pretty common on trucks here in Pa. We've seen problems with them cracking. Quote Link to comment https://www.bigmacktrucks.com/topic/34106-2009-mru-w-mp7-coolant-in-fuel/#findComment-224847 Share on other sites More sharing options...
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