Jizzo17 Posted September 30 Share Posted September 30 (edited) I’m having a coolant issue on my 1985 Mack r with a em6-300. VIN is 1M1N179YXFA099577. I have flushed the coolant system at least 8 times with cascade powder. It was finally running out clear when I drained it so I put my new thermostat in, new water filter, and filled the radiator with the red coolant and distilled water at around a 55/45 ratio. It was holding temp at 180* with a few test runs I made but I was hauling gravel today and it got up to 230+. I wasn’t concerned at first thinking it might be a faulty gauge or sensor, but it started puking water out of the radiator cap. I parked it and let it idle but it still never came back down below 220. The fan feels like it’s pulling a good amount of air through the radiator. So I’m led to believe it may be the water pump. Has anyone else had any similar issues? thanks. Edited September 30 by Jizzo17 Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/ Share on other sites More sharing options...
Joey Mack Posted September 30 Share Posted September 30 Cavitation in the water pump housing. ?? Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583638 Share on other sites More sharing options...
Jizzo17 Posted September 30 Author Share Posted September 30 13 minutes ago, Joey Mack said: Cavitation in the water pump housing. ?? How would I check for this? I may end up ordering a new water pump and slapping it on regardless. Would a new fan clutch be recommended as well? Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583639 Share on other sites More sharing options...
Joey Mack Posted September 30 Share Posted September 30 When you pull the water pump, the inside of the housing will be visible. If its pitted real bad, it needs to be replaced. Yes to a new viscous fan clutch. Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583640 Share on other sites More sharing options...
Geoff Weeks Posted October 2 Share Posted October 2 More likely to be plugged tubes in the radiator, with a history of 8 flushes to get the clear water. Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583726 Share on other sites More sharing options...
Joey Mack Posted October 2 Share Posted October 2 Are willing to take the radiator out and remove the tanks to inspect the tubes ? Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583727 Share on other sites More sharing options...
Popular Post Geoff Weeks Posted October 2 Popular Post Share Posted October 2 5 minutes ago, Joey Mack said: Are willing to take the radiator out and remove the tanks to inspect the tubes ? If you are asking if I am, no! However a 40 year old cooling system that has been neglected to the point it takes 8 flushes to clear it is most likely. Water pump pull is easy, but I would be surprised that a water pump alone would cure the problem. The age of the radiator has not be established to my knowledge, but if more than a few years old, it would be suspect. Human nature to look for the easy solution, but a well maintained will be clear inside after years of running. One that isn't will be gooky, this one is (or was) gooky. 4 Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583728 Share on other sites More sharing options...
Jizzo17 Posted Saturday at 01:21 PM Author Share Posted Saturday at 01:21 PM (edited) On 10/2/2025 at 11:29 AM, Geoff Weeks said: More likely to be plugged tubes in the radiator, with a history of 8 flushes to get the clear water. I was afraid it might be the radiator. The old pump has a date stamped ‘86 on it but was not pitted and turned fairly easy when separated from the fan clutch. The fan clutch itself still had resistance. I have the radiator detached to the point where I was able to lean it forwards and pull the pump and fan out as one unit. So a few more hoses to unhook and I can lift the Rad out. Being as the pump was original I would bet the radiator is also original to this truck lol i am getting coolant flowing throughout the cooling system. Would plugged tubes still allow that? Edited Saturday at 01:35 PM by Jizzo17 Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583799 Share on other sites More sharing options...
Joey Mack Posted Saturday at 05:05 PM Share Posted Saturday at 05:05 PM It flows through the heater core if the valve is open and the open tubes in the radiator. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583804 Share on other sites More sharing options...
Jizzo17 Posted Saturday at 07:08 PM Author Share Posted Saturday at 07:08 PM What is the round tube that the water pump forces water into? It’s in front of the 3 oil filters on the driver side of the engine. Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583806 Share on other sites More sharing options...
D-Day Posted Saturday at 08:39 PM Share Posted Saturday at 08:39 PM It sounds like you are describing the oil cooler 1 Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583809 Share on other sites More sharing options...
Joey Mack Posted Saturday at 09:06 PM Share Posted Saturday at 09:06 PM Oil cooler... Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583813 Share on other sites More sharing options...
Jizzo17 Posted Saturday at 11:49 PM Author Share Posted Saturday at 11:49 PM 2 hours ago, Joey Mack said: Oil cooler... 3 hours ago, D-Day said: It sounds like you are describing the oil cooler Thanks. I thought so. Would it be possible for it to be plugged as well? Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583822 Share on other sites More sharing options...
D-Day Posted Sunday at 01:44 AM Share Posted Sunday at 01:44 AM It is possible I have found gobs of silicone and rust chunks blocking the cooling tubes but that should not affect the coolant temperature overall but would affect the oil temperature more if it was severely blocked it could restrict the overall flow of the cooling system slightly 1 Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583831 Share on other sites More sharing options...
Jizzo17 Posted Sunday at 11:15 PM Author Share Posted Sunday at 11:15 PM Here is a picture of the oil cooler tubes. I ran a wire through several of the holes and there is some sludge inside. Could I just blow air through them or can they be replaced? Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583854 Share on other sites More sharing options...
Joey Mack Posted Sunday at 11:51 PM Share Posted Sunday at 11:51 PM Did you pressure test it before taking the end caps off ? Do you have new gaskets for it ? I have to ask.... Are you familiar with this oil cooler? Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583855 Share on other sites More sharing options...
terry Posted Sunday at 11:53 PM Share Posted Sunday at 11:53 PM The whole bundle can be replaced, Joey might have a idea on cleaning it. terry Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583856 Share on other sites More sharing options...
terry Posted Sunday at 11:58 PM Share Posted Sunday at 11:58 PM Been alot of years since i checked one, don't remember if i put low air pressure on the oil side or water side and put it in a tube of water to check for bubbles. terry Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583857 Share on other sites More sharing options...
Jizzo17 Posted Monday at 12:04 AM Author Share Posted Monday at 12:04 AM (edited) 13 minutes ago, Joey Mack said: Did you pressure test it before taking the end caps off ? Do you have new gaskets for it ? I have to ask.... Are you familiar with this oil cooler? I just took the forward facing end cap off. It’s the one that bolts to the water pump. The system will pressurize because it will blow the cap off the radiator if you remove it when it’s hot. i don’t have new gaskets but I can cut some out or get my Mack dealer to order some. I bought this truck from a lumber yard with 560k+ miles. I added the plus because the odometer stopped working at some point and there’s no telling when that happened. So I’ve become increasingly familiar with this truck the longer I’ve owned and operated it. But this is my first time with this type of oil cooler. Edited Monday at 12:05 AM by Jizzo17 1 Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583858 Share on other sites More sharing options...
Joey Mack Posted Monday at 12:14 AM Share Posted Monday at 12:14 AM Pm me your address and i will send you a set of orings and gaskets. I have a few. The oring set has 2 different sizes and is hard to see, you have to stack them to see the small difference. Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583860 Share on other sites More sharing options...
Jizzo17 Posted Monday at 12:18 AM Author Share Posted Monday at 12:18 AM Okay thanks will do. do you advise taking the entire oil cooler off before I blow air into it? Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583861 Share on other sites More sharing options...
Joey Mack Posted Monday at 12:41 AM Share Posted Monday at 12:41 AM yes to removing the cooler. however, you already broke a gasket seal, so it would need to be put back together tightly and sealed. I can take a picture of my test tools. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583863 Share on other sites More sharing options...
Joey Mack Posted Monday at 01:05 AM Share Posted Monday at 01:05 AM (edited) it is pressure tested at 80 PSI.. here is my home made kit that works. you will cut your own gaskets.. Edited Monday at 01:14 AM by Joey Mack spelloing 1 Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583864 Share on other sites More sharing options...
fjh Posted Monday at 02:41 PM Share Posted Monday at 02:41 PM On 9/29/2025 at 7:51 PM, Joey Mack said: Cavitation in the water pump housing. ?? Buddy I would lean towards a fan hub on this! 1 Quote Link to comment https://www.bigmacktrucks.com/topic/76002-em6-300-water-temp-230/#findComment-583880 Share on other sites More sharing options...
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