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Old 01-06-2021, 08:11 AM   #1
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Oil in coolant, replacing oil cooler - Tips/Advice? C8.3 Cummins Diesel

Hi!
I have a 1994 Coachman with an C8.3 Cummins. I check the engine/fluids every hundred miles, and last time I checked I had oil in the coolant. No coolant in oil, and no noticeable drop in oil level. From the research I've done it's most likely the oil cooler, which I plan on replacing this month before going from FL to CO. I haven't been able to find much using the search feature or through google, and have some questions for anyone that has experience replacing one of these. The biggest problem I see so far is accessibility. It's tough to reach the bolts and theres a giant bundle of hoses/wiring running right in front of it. Any tips or advice is greatly appreciated!! Thanks!!

These are the steps I understand I need to do. Am I missing anything?
1. Clean area around oil cooler cover
2. Drain coolant
3. Remove oil filter
4. Remove oil coolant cover
5. Remove oil cooler/gaskets
6. Install new oil cooler/gaskets and reinstall cover
7. Reinstall oil filter (same or new?)
8. Fill coolant with water and half bottle of dawn dish soap
9. Let run for 30 minutes including driving on road
10. Drain coolant, refill with water only and flush 2-3 times or until clear.
11. If no oil is present anymore in water, drain and replace with coolant/antifreeze.

Other questions:
1. The oil cooler from Cummins is $300. I've found aftermarket ones for around $150. Is this a part you can comfortably replace with aftermarket, or should I spend it extra and buy from Cummins?
2. How long should I drive before being confident no other oil is leaking into coolant before refilling with coolant? The coolant alone is a couple hundred bucks so I don't want to do it too early. Days? Weeks? Miles?
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Old 01-06-2021, 11:43 AM   #2
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Only my $0.02
.....I would not suggest using the Dawn soap in the cooling system. I have many times used a small box of powdered Cascade dishing washing detregent. It will not foam, bubble and is way easier to rinse out that what your thinking....very safe on engine metals as well....also no need to run it down the road, just run the engine at 1200 or so RPM at operating temp for 30/45 mins, and flush with water

Don't reuse oil filter and replace coolant conditioner filter

I got no issues with the aftermarket cooler....but I've never used one

Be sure it's engine oil in colant, the Transmission heat exchager can put ATF into coolant as well.....

BUT.....think about this. Which ever cooler it is, trans or engine oil, there's also coolant in that component as well.
.....when the engine is running and at operating temp, the coolant system has between 10 to 16 PSI, while oil pressure is 40+ psi the higher psi is forcing oil into coolant system......BUT once engine is shut down oil psi (or trans fuild psi) goes to zero while coolant psi is STILL at 10 or more psi unitl eninge cools down.....this will push coolant into the oil or fuild.

....either way, expect to change either engine oil or trans fuild depending on which heat exchanger you find defective....

It's no a bad job to replace either heat exchanger, only the RV chassis make it a PITA
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Old 01-06-2021, 04:49 PM   #3
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Thanks for the tips @mackwrench. Yeah I wasn't looking forward to getting all the suds out of the system from the Dawn. I will look into the Cascade option.

The engine being in a big truck instead of an RV would for sure make it easier. With easy access it looks like a pretty quick job actually replacing it. As it sits, the bolts look to provide a knuckle-crushing afternoon.

I'm pretty confident it's oil, not transmission fluid from the color/smell. But I will double check.

That's the first I've heard about having to change the oil. It makes sense though. I just changed it oil 1k ago, so was hoping to avoid replacing it all again if possible, since I've only driven a few miles since it started leaking (I check it pretty often). But will change it if needed of course. The fluids, between the coolant and oil plus filters end up being the largest cost to this repair it looks like. Good and bad I suppose.

Thanks again!
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Old 01-06-2021, 05:08 PM   #4
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I would suggest you use Fleetgard Restore product for cleaning your cooling system. It is formulated for Cummins engines.They have a chart on the second page of the link bellow that out lines both Restore and Restore II products. I used II since I was mainly flushing the system but did not have oil contamination. You might be able to have a radiator shop test your old cooler to verify that was the bad part. It would be an easy test. You need to be sure you have the correct diagnosis. Let us know how you do!

https://www.cumminsfiltration.com/si...es/lt36625.pdf
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Old 01-06-2021, 06:15 PM   #5
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+1 on the Restore...and once off oil cooler easy to test using some fabed up block off plates and shop air.

It sounds like OP ain't got a big leak or it'd be blowing coolant/oil slick out of expansion tank! I've seen this happen and it's a mess.

I have used the Fleetguard restore flush. It good stuff, a little pricey, and if you're coolant system has rust and scale from lack of system maintenance it's the way to go.

Hopefully his coolant system is in good condition & the OP is only trying to flush the engine oil from the system. Old school techs used Cascade powder for just that. Quick, safe and cheap, lol

I've heard it's tuff on aluminum, but only when exposed to long term use. Like washing a aluminum pans a hundred times in a machine, lol.

I've never had / seen any ill affects from flushing a coolant system with it.

Good luck and keep us posted!
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Old 01-08-2021, 08:34 AM   #6
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Thanks Bruce, I'll look into the Fleetguard restore too.

I definitely want to get the old one tested if possible. I'd hate to get it all back together with new fluids and still have a leak. I've been having a bit of an issue finding a shop to test it though. All but one I've asked have said they can't, and the one said they'd have to see it in person to see if it would fit and if they have the right blocks. They also said they can only test up to 25psi. Is that enough pressure to properly test or does it need to get up to the 80psi or so like operating temp under load?

@mackwrench It doesn't seem to be a big leak. When I found the issue there was an inch or 2 of visible oil floating at the top of the coolant overflow, and I could see some oil in the viewing window of the main reservoir. I had to drive 40 miles after that to get home and didn't notice much more oil in the overflow, and no noticeable drop in oil level. The oil in the engine doesn't seem to show any coolant or milky color on the dipstick. I also check it every trip, so it would have only been an issue for no more than 30 miles or so before I found it.

Anyway I'll update when I have more info. I plan on leaving cross country on the 15th of February (4th year in a row chugging this old thing to the other side), so I have 5-6 weeks to complete it and will start on the removal next week. Thanks!
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Old 01-18-2021, 05:45 PM   #7
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UPDATE

I replaced the oil cooler and both gaskets today, and nothing blew up!

The worst part was just the location of the cooler and cover, and the complete lack of room and access. Overall it was a surprisingly easy job and saved me about $1500-2k based on what I was hearing on quotes.

For flushing, I had the Dawn dish soap option, Cascade dishwasher detergent, and Fleetguard or similar professional cleaner. I went the the dish soap (make sure it's "dawn" I hear). The worst thing I heard about it is it's hard to flush out. The Cascade I kept coming across warnings of eroding or etching internal parts (which is still up for debate), and the professional cleaner I'd have to order. The local NAPA/Auto Zone didn't have anything that made it clear it would cut through oil. The advice I got from the local diesel mechanic is to put half a small bottle of dawn in, run it 25 minutes, then open the petcock valve on the radiator, and keep filling the reservoir until both sides show no suds (and then another 5 min or so). So that's what I did. I will also do another full drain and refill, then will drive it a couple hundred miles before I do a final drain and refill with coolant vs water and replace the filter.

Oil: I ended up skipping the oil change. The dipstick, drain plug and filter showed absolutely no signs of coolant, moisture or bubbles and no other signs of contamination. I just recently changed it and it still looks new, so I'm going to go with saving the bit of money for now.

Torque: I haven't been able to find anything about torque. I turned "until it felt right", and nothings leaking or broke, so I'll leave it at that unless I find out more.

I could never find anyone local that said they've be able to test the oil cooler, but with the effort it took to remove I'd replace it anyway. I'll keep an eye on the coolant/oil and see if any other mixture occurs.

Thanks for the help and I'll send an update if anything new comes up in the future.
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Old 01-18-2021, 07:39 PM   #8
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Woo-hoo! You won
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Old 01-20-2021, 08:56 PM   #9
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I purchased my 2008 Phaeton in 2019, it had the Cummins 360 replaced at 48000 miles by Cummins (factory defect), the owner at the time later found out that oil eats radiator hoses, a bit of info that Cummins didn't inform him of, he then replace all the hoses at his expense, the Dawn may work or it may not, be aware that it may not and you may have an issue down the road
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Old 01-20-2021, 09:20 PM   #10
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The Dawn is the right stuff to clean out the oil.

We used it after oil contamination in truck engines many times. Just do the hot rinse 3-4 times.

Just a little trick to check for coolant in your oil is to take a small sample, pour some onto some carboard and light it on fire. If there is any water in it, it will pop and crackel as it burns. Steady even burn, and there's no water in the oil.

We had made up plates with fittings to add air pressure to test oil coolers. Just air them up and put in a tank of water. Use low (3-5 psi), and high 40-50 psi) to test it.
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Old 01-21-2021, 08:52 AM   #11
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Unplanned: Thanks for the tip on checking for water in oil. When you say 4-5 times on the hot rinse, are you using dawn multiple times, or just the first time, and hot rinse with just water after that?

Out of the 10 gallons or so of coolant I initially drained out into buckets, I only had a very thin layer of oil film floating on top. I'm still concerned about the hoses, as I've heard before that oil can damage them. But I'm hoping the amount of oil and short time being contaminated that I can get away without having to replace them all.

AJM: A new engine at 46k miles sounds pretty rough. Are you saying the he had oil in the radiator hoses on the NEW engine, or is that what killed the last one?
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Old 01-21-2021, 09:58 AM   #12
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With just a small amount of oil in the coolant, just flush with Dawn once, then straight water with a little Calgonite for the next 2 times, then straight water.

Be sure to flush the heater and all other hoses. We always used silicon hoses that weren't affected by oil or heat. If you have regular rubber hoses, just feel if they are soft anywhere. If soft, replace them.
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Old 01-21-2021, 12:04 PM   #13
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Quote:
Originally Posted by Unplanned View Post
The Dawn is the right stuff to clean out the oil.

We used it after oil contamination in truck engines many times. Just do the hot rinse 3-4 times.

Just a little trick to check for coolant in your oil is to take a small sample, pour some onto some carboard and light it on fire. If there is any water in it, it will pop and crackel as it burns. Steady even burn, and there's no water in the oil.

We had made up plates with fittings to add air pressure to test oil coolers. Just air them up and put in a tank of water. Use low (3-5 psi), and high 40-50 psi) to test it.
How much is the adequate amount of Dawn Ultra dishwashing liquid, take OP's case as an example, like 12 oz or 20 oz?
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Old 01-21-2021, 02:37 PM   #14
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How much is the adequate amount of Dawn Ultra dishwashing liquid, take OP's case as an example, like 12 oz or 20 oz?
12 oz in 10 gallons usually does the trick. If it's really bad, you may have to do it 2-3 times. Just be sure to get it hot enough to open the thermostat, and run for a while. You want to circulate the soapy water through the whole system.

We had a set-up that put hot water into the bottom rad hose while the engine was running. That way the oil would go out the rad cap location (rad cap off).
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