I drained the coolant out of a 1974 Cummins ntc 350 and found some oil in the coolant, I would guess 2 cups. The owners know little about the truck and I would guess it has been many years since the coolant was changed. There doesn't appear to be any coolant in the oil and it seems to run fine at idle/high idle. I haven't run it on the road yet. Is this indicative of a cracked block/bad head gasket or is there a likely less ominous cause? Thanks, DBS
Is there an oil cooler fitted to the engine? That's the most likely place for it to leak. Your oil pressure is greater than your coolant pressure so it sends oil into the coolant. You can pressure test the oil cooler to see if it's leaking. To flush your cooling system, just pour some Cascade dishwashing soap into the system and run it a while. You may have to do it more than once, but it'll clean it up great.
Thanks for the great info. It does have a full flow oil cooler as part of the engine coolant system. Any ideas on how to pressure test the oil cooler. I'm going to pressure test the radiator tomorrow. If the pressure in the radiator rises quickly as is elevated I assume that would likely not be due to a small leak in the oil cooler. Thanks, DBS
If you don't know anything about the engine's previous history I'd go with Don's idea and start by cleaning the cooling system out with Cascade or similar until you know it's clean. That gives you a point from which you can start keeping an eye on things and if oil starts to appear in the radiator again you will have to go to a deeper diagnostic.
This case is the one way an oil sample analysis can save you a ton of money and probably the only time I recommend a single sample for analysis. Oil coolers will leak engine oil into the coolant when the engine is running. However when the engine is shut down there will still be pressure in the cooling system and the oil pressure will be zero. Coolant in the engine oil is a far more serious problem. If the sample shows lots of lead along with copper, then your problems go much deeper than a leaking oil cooler.
To check for coolant in engine oil (a distinct possibility if it's a cooler leak, the transfer goes one way when you have oil presure and the other way when you shut down a hot engine) depending on the type of coolant being used you need to look for either sodium or potassium in the oil analysis. That's for small amounts, some analysis will run a test for the presence of glycol but that does not work with some of the newest organic-acid-based coolants. I'd still clean the radiator first then go from there.
Nige, You are right about the the additive packages but I'm looking for damage to the bearings. If I have leaching, I'm thinking of in frames or rebuilds as well as cleaning radiators. The difference will influence how I think of the future of using that piece of iron.
John, unfortunately a one-off sample isn't guaranteed to prove whether you have or don't have bearing damage. In my experience an engine with coolant contamination in the oil will see a spike in lead & tin as the coolant attacks the LTO in the crankshaft bearings for probably 1-3 samples (if oil is sampled at intervals of 250 operating hours) at most. After that lead numbers will return to the same level as they were before (typically bouncing between 0-1ppm). At that point the LTO surface on the crankshaft bearings has been pretty much destroyed but the sample results won't tell you this. Hence my suggestion to check for sodium/potassium because even if the crankshaft bearings are not producing lead because there is no lead there any more, there will still be indications of the coolant in the engine oil sample.
Never seen an engine that would run after the lead was all gone from the bearings. I have seen bearings leached out after 50 hours of run time with coolant in the bottom.
Nige, How much Cascade would you and to the radiator. My coolant volume is about 12 gallons. Thanks, DBS
dbs, I had a 425 cat with the same problem, I changed the oil cooler and that did'nt fix it. Cat told me that the front seals needed changed, however I let it go for to long and ended up with an in-fr.
About 1-2 cupfuls I'd guess, but overdosing it won't hurt anything. Get that into the system and let the engine run at operating temperature for a good while to circulate it and get the oil out of all the nooks & crannies in the engine. The great thing about something like Cascade is that it doesn't foam so you can run the system with the radiator cap on. The critical thing is to check the water/soap mixture as you drain it. If it's uniformly a sort of grey colour you've probably got all the oil in one hit, but if you can still see streaks of black oil in what you're draining, repeat the process until the radiator is completely clean. Then run it up to temperature with clean water to rinse, drain one last time and fill with coolant.
Nige, Thanks for the quick response. I talked to the Cummins dealer and they said it is not uncommon for the oil cooler to leak in these old engines. They said to take the oil cooler off and bring it in and they can test it to find out where the leak is. From the old oil deposits near the top of the radiator it looks like it has been leaking for some time. On the up side the engine seems to run flawlessly. If I could bother you with a couple other questions. Is it common for these engines to fail to start without preheating below 40 degrees? Also my amp meter shows the alternator over charging at greater than 16 volts. Any thoughts. Thanks again for the great advice, DBS
Yes, it is common for these engines to start hard at those temps. Mine won't start at 50 with out a preheating or either. I've been told it is dependent on where the timing is set. For your charging question.. If the gauge is reading 16 volts, then you have a voltmeter not an ammeter. 13.5-14 volts would be normal. I would test or have the system voltage tested to see what the actual voltage level is. Your gauge could be faulty or your alternator could be over working itself. Do the batteries seem wet on top? Do you need to add water to them occasionally? These would be signs of over charging.. Hope this helps. I'm curious, what brand and model of truck is this motor in?
your question's already answered by the gentleman above. Nothing more to add really. Even if it's proved that the cooler was the source of the oil remember that you'll still have to thoroughly clean the system out with Cascade before you can fill it with coolant again.
Smb, The Cummins dealer, a mechanic with 30+ years of experience felt strongly that the full flow oil cooler was the culprit, but I'll keep your experience in mind. Thanks, dbs
Markat, This is in an International Transtar 4300 tandem axel dump truck. Dbs
Small world, I guess ! Here's mine. It also spent most of it's life in Alaska.
Mine is a '74. It was wrecked and rebuilt so it carries a '81 title. During the rebuild is when it had those square headlight bezels installed instead of the round ones that a '74 would have. I found an Overdrive magazine in it that was from the early '90's, the address label was for a guy in Anchorage. I don't know if he was an owner or a driver. I bought it from a guy that was stationed up there with the military. He used it to move his family to Florida, where I bought it and hauled it to Indiana. The engine is the same as yours, NTC 350 small cam Cummins, 13 speed, Reyco spring suspension, aluminum frame, no corrosion but some of the biggest stone chips imaginable..
Markat, Interesting, mine has the Fuller 10 speed trans. The mileage on mine is unknown but it seems to run near perfect. It produces only a small amount of smoke and no substantial blowby. Mine seems to have an aftermarket device on the dash board. It is a short piece of 1/4 or 3/8 pipe that is used as a handle to pull out a cable that disengages the starter motor from the ring gear(fly wheel) and allows you to spin up the starter motor to a high speed before engaging ring gear thus allowing the starter to have much more momentum to get the engine turning. It seems to work well and apparently doesn't damage the ring gear as I just replaced the started and the ring gear appeared in great shape. dbs
That should be your compression release I believe. That'll make it spin a lot faster.
Yup,, a compression release. It wasn't aftermarket, it would have been factory installed. Mine has a couple of slight modifications done by a previous owner. All of the fuel lines are wrapped with some kind of really tough insulation material. Also, the A/C unit under the passenger seat has been disabled and converted to have coolant flow through it, making it a second heater core. It also came to me with the largest engine block heater I have ever seen. A 2250 watt circulating tank type unit. I can plug it in at 10 degrees, wait 30 minutes and the engine will be 140 degrees.