7.3L Power Stroke Oil Cooler Reseal/Replacement and Pressure Test

How to reseal or replace the oil cooler on a 7.3L Power Stroke. The procedure is pretty much the same for all 7.3 trucks from 1994.5 to 2003. I also show one way to pressure test the oil cooler itself, because that was actually my problem.

[@213madd9]

Love how you didn't cut all the bs out of the video like spilling that oil because we all know that's how it goes and it was a nice warm up watching you do it prior to starting the job

[@darkhorseautoanddiesel]

I like realism in my videos 🤣 I imagine you got a laugh out of the pressure test failing on me the first try as well 🤣

[@7.3Devo]

one of the best videos on youtube about the obs 7.3 oil cooler! no one has a detailed video like this!! even a year later still giving some valuable knowledge!

[@darkhorseautoanddiesel]

Exactly why I started making videos! There's a lot out there that suck! I'll never say mine are the absolute best, but I try. Comments like yours keep me motivated to make more content.

[@zach_hewitt]

first video I've seen with someone actually showing the block plugs!

[@christianhilditch9333]

Thank you for sharing. I just bought a 99 super doody. She needs alot of love. Looks like i need one. I love how raw your filming is. The pressurized vessle on the bence right next to the jugs of oil on the healing bench was pure anxiety.

[@WayneWilson10]

this is the most relatable repair video i have found on youtube.

[@johnmclaren7059]

Dirty job! I did my 97’ 10 years ago now it’s time again after I noticed a leak after start up on a cold winter morning 😢 these do fail but keeping your truck plugged in during winter keeps the oil warm ! Never had sludge in my coolant…. Yet ! Great video brother! Keep the ol girl rolling 👍

[@darkhorseautoanddiesel]

Thanks! Yes, very dirty. I would keep it plugged in any time im not using it, but after doing the math on what it costs, I decided against it a long time ago. I'll definitely keep it rolling until the cab rots off the frame!

[@shadrack9986]

My says plug it in 3 hours b4 you leave,what's the length you can leave it plugged in time wise ?

[@darkhorseautoanddiesel]

3 hours before you plan on starting it is usually sufficient to get it started and have pretty much instant heat in the cab. If you don't mind paying the extra electric bill, you can leave it plugged in 100% of the time you aren't driving it. As long as your cord is in good shape, it won't hurt anything besides your wallet. A 7.3L block heater draws 1000 watts, which means it uses 1 kilowatt hour (kwh) of electricity per hour. If you look at your electric bill you can find what you pay per kwh and multiply it by how long you want to leave it plugged in, then decide how much you want to pay.

[@Gotya02]

Great video. Love the 7.3

[@darkhorseautoanddiesel]

Thanks! I do as well, I own 2 of them for a reason.

[@resurgence6169]

I appreciate you making this video more than I can say. The shop freaked me out for a moment saying that I needed a new head gasket, but no coolant in oil, so I'm pretty sure it's just the cooler and will be doing the same soon

[@victornunez8267]

Best thing to use as well is those cheap plastic kiddie pools you cand get at lowes or Walmart for less than $10. Big enough to help catch all fluids and keep off of the floor.

[@swtguy401]

Thanks for the video man. Unfortunately my dumbass has done this job a total of twice. Thinking I screwed up the gaskets somehow because pressing it together was absolutely awful in my situation. Looks like 3rd time may be a charm I hope. Gonna pressure test the actual cooler. Rookie diesel mechanic here

[@darkhorseautoanddiesel]

How did it turn out for you? This video was the 2nd time I'd done this job on this truck because I cheaped out on the oil cooler.

[@chuckparson6712]

Great detailed video, thanks for sharing 👍👍

[@darkhorseautoanddiesel]

You're welcome. Thanks for the compliment.

[@miguelmendez4690]

good video my friend bless you and America 🇺🇸 from Guatemala 🇬🇹 here from NJ

[@Gimmeanother]

Nice Job! I hope I don’t ever need to do it on my 7.3 but I’m sure glad you made the vid on how it’s really done ~ Thx

[@darkhorseautoanddiesel]

Glad you liked it! It's definitely not a fun job.

[@JoseGarcia-pd5bo]

thank you for the video!!! thank you for real world experiences!!!

[@ZackNunn-mb4mi]

Really saved me I thought my crank seal was out

[@darkhorseautoanddiesel]

I'm glad my video was able to help you. Oil cooler leaks are common when the weather gets cold.

[@blazanhaydutis8454]

This video was so funny and informative

[@darkhorseautoanddiesel]

Thank you! I try to add some humor and entertainment value into an otherwise dry and boring category of video. A lot of how to videos can be rather difficult to watch. Not saying mine aren't but at least I try 🤣

[@johncraig406]

Great Video, thank you so much. hope I never see that goo in my coolant, but now I am not so afraid of replacing the oil cooler. I assume any "coolant flush" product will be okay, as the final flush will be plain water?

[@darkhorseautoanddiesel]

Thanks! I've never used any "flushing" products, I've just always used tap water, then one final flush with distilled water since tap water can have a lot of minerals and stuff in it that can cause corrosion. Whenever I do another coolant flush on one of these trucks I'll definitely be making a video on it, but as of right now I've never filmed it. I didn't actually do a flush after I finished this job. I managed to drain enough goo out that the little bit that remained in the system floated to the top of the coolant bottle, and from there I just used a suction gun to draw it out as it appeared. If it was a customer vehicle I would have flushed it for sure, but it's one of my trucks so I knew I could get away with doing it that way.

[@hfdzl]

Great content, I have to do mine also. Would help to jack up motor about an 1in or so , put a block under the motor mount.

[@darkhorseautoanddiesel]

I've heard of people doing that. It definitely would give you more room. I guess I've just been lucky enough to get them out easy enough that in my mind it wasn't worth the extra work.

[@bobobrazil1973]

Dude it's a 7.3 it will run on anything 😂

[@darkhorseautoanddiesel]

@@bobobrazil1973 Pretty much! And thanks to a buddy of mine's truck, I've also learned that apparently they really don't need any oil pressure either! His truck for some reason would drop to, at most, 5 psi at anything over about 1000 RPM (never did figure out why), did that for a several thousand miles, sold the truck, and last I knew it was still going. It has 238/100 injectors and he wasn't nice to it either. 🤣

[@michaelbenoit248]

Did this job years ago & gotta do it again because the cooler block gaskets are leaking. Gonna use anaerobic spray sealant this time. DO NOT rtv.

[@wyattc9273]

I’m having the same problem it’s just darker goop but it doesn’t over heat or anything and I’m praying it’s the oil cooler

[@darkhorseautoanddiesel]

Most like it's the oil cooler. While it's not impossible, a blown head gasket on a 7.3, especially a stock one, is extremely rare. I've heard of it happening, but I've never actually seen it.

[@Chardy3800]

Done several of these on International trucks and school buses. Much much easier than a pickup. This can be one nasty job no doubt

[@darkhorseautoanddiesel]

I would imagine that trucks and busses would be much easier. I'm sure there is WAY more room to get that thing out of there.

[@victornunez8267]

And another tip is to replace the drain plug on the block with a hex head helps with next time for removal due to the allen sometimes stripping due to heating and cooling especially if they original plugs

[@rubenguerrajr5833]

The first video I saw on this type of work I need done to my 7.3. Question, I, currently, do not have the oil sludge in the radiator BUT i do have a leak near the end cap of the oil cooler near the block heater cord. Does this mean that just the gaskets need replacing and not the engine oil cooler? I just turned her on one morning and saw the leak coming down. For a moment i thought it was a freeze plug but after careful looking, it was the top of the oil engine cooler near the block heater cord connection. Will it i be safe if i just replace the gaskets and O rings?

[@darkhorseautoanddiesel]

Yeah I would say it's just the orings. It's pretty common on these trucks as they age. You usually notice it in the winter on cold starts, then it stops leaking after running a few minutes. Obviously it can happen in warmer months as well though. If there is no suspicions of oil and coolant mixing, and the gasket mating surfaces are in good shape, I'd say just reseal it and run it.

[@rubenguerrajr5833]

Thank you so much for the reply back. I will go into the job myself with that in mind now.@@darkhorseautoanddiesel

[@darkhorseautoanddiesel]

@@rubenguerrajr5833 You're welcome. Helping people is the main reason I started making these videos. It is not a fun job by any means, and it can get very messy, but you'll save a lot of money doing it yourself versus taking it to a shop.

[@psalm6408]

You mechanic a lot like I do, but with fewer expletives.

[@darkhorseautoanddiesel]

I try to keep my channel PG-13, so those parts get cut out haha. If I didn't edit the way I do, my channel would probably be rated R.

[@JaredWilliams-y3k]

When you replace the oil cooler how do y’all flush the jackets in the block and do you recommend replacing the cooler before you flush it?

[@JaredWilliams-y3k]

In our case the cooler failed causing the oil and coolant to mix

[@darkhorseautoanddiesel]

I've heard of people putting dishwasher detergent in the cooling system to clean oil out of it, but it can be quite corrosive, so you have to be careful with it. In my case here, this is my own truck, so I never actually flushed the system. The oil left in the system will always work its way to the top, so it collects in the reservoir where you can use a suction pump to draw it off every now and then, which is what I did. If it was a customer vehicle I would have flushed it.

[@nemideergoon1844]

Replace coolant with simple green /water. Or get some motorcraft VC9 ($50 quart)

[@repairvehicle]

Oil causes rubber to swell up and fail if it’s not meant to be in contact with oil. Coolant works really as lubricant too.

[@darkhorseautoanddiesel]

Yes oil and rubber don't get along. About 3 months after this my upper rad hose blew out pretty spectacularly 🤣 Coolant does work as a lubricant, in the cooling system, not so much on bearings that are supposed to be in oil though 😆

[@repairvehicle]

@@darkhorseautoanddiesel you still own this 7.3?

[@darkhorseautoanddiesel]

@@repairvehicle Sure do. Got around 530k miles on it now.

[@repairvehicle]

@@darkhorseautoanddiesel , what repairs have you done to the engine? Any blow by? Original transmission? I’m thinking about getting one of those 7.3.

[@darkhorseautoanddiesel]

The engine itself, as far as I can tell, is all original. Blowby is at normal levels. It actually has slightly less than some engines I've seen with less than half the miles. I've had it out of the truck once, but that was only to replace the rusty oil pan. While it was out I did some freshening up to other components, like rebuilding the turbo (no problems with it, just figured I'd do it since it was already off the engine, also installed an upgraded compressor wheel), new exhaust manifolds, fuel system orings, and a new oil cooler (which is the bad one in this video). Probably a few other things I'm not remembering as well. Definitely not the original trans. When I bought the truck (had 314k miles on it at the time) the previous owner told me he had it rebuilt around 100k miles prior. I ran that one for about 50k more miles (I think, I'd have to look at my maintenance log), at which point I pulled the pan to change the filter and saw fairly large chunks of metal stuck to the magnet. Part of a bearing assembly. At that point I pulled the BTS trans out of my other truck and put it in this one. Since this one is my work truck and at times gets driven out of state, 100% reliability was important. The other truck was already lined up for a ZF6 swap anyway. If you are thinking about getting one, do it. Just make sure it isn't a sacked out POS. Check the blowby. Look at the air intake tube between the filter and turbo and make sure it's clean. Jump the stater solenoid on the fender with the key off and listen to make sure it spins over evenly. If you do buy one, if it has an auto trans, just set aside the money for a rebuild and expect to spend it at some point. Also keep a spare OEM cam sensor in the glove box, and a 10mm socket to change it, should the need arise. There's more advice I could give, but I've already typed a short story 😆

[@brad6523]

I have the same issue. Oil in coolant. A mechanic told me I need to replace my entire cooling system. Radiator and lines. I thought a good flush would be fine. How did the flush work out for you? Any issues?

[@darkhorseautoanddiesel]

Radiator will be fine. If it's like that for a long time I'm sure the oil could possibly degrade the plastic, but I wouldn't worry about it. I did have to replace the radiator in this truck several months after doing this job, but I doubt it had anything to do with this problem and had everything to do with it being over 20 years old and going through countless numbers of heat cycles over the course of around 500k miles. The plastic split right at the upper hose attachment. I did have the upper hose blow out on me though, and I do contribute that to the oil in the coolant, the rubber was really soft. I would recommend replacing the upper and lower main hoses if you have this problem, but I wouldn't be concerned about any of the others. I'll be honest, I never did flush the system. All I did was use my vacuum brake bleeder to pull off the layer of goo that accumulated at the top of the reservoir every once in a while until no more was visible. Truck is still running fine.

[@hondaxl250k0]

So if oil is in just the Coolent but no water in oil. Can it still be driven? I ask being on vacation and just noticed a film after the drive .. got about 400 miles home. No trailer. No real load other than hills.

[@darkhorseautoanddiesel]

The trick to keeping coolant out of the oil is to vent the cooling system pressure after you shut the engine down. When the engine is running, the oil pressure is higher than the coolant pressure (unless you have an oil pressure problem), allowing oil into the coolant. Once you shut the engine down, obviously your oil pressure drops to 0, but the cooling system slowly drops from around 16 psi as it cools, which can take some time, allowing coolant in the oil. As long as its not a horrible leak, you should be ok to get by with that to at least get you home. Just remember to tighten the coolant cap before you start it, and unscrew it every time you shut it down. Chances are, you have coolant in your oil, just not enough for you to see it. I only knew about mine from an oil analysis. How long you can get away with that? Well, I'd recommend fixing it ASAP and driving as little as possible until it's fixed. For me, since this is my work truck and my primary source of income, and was very busy with work at the time, I did this for about 6 months, and was driving a 9 hour, 520 mile round trip every other day for about 3 of them 🤣 I would NOT recommend anyone else do the same. I took my chances with the hope that it wouldn't turn catastrophic. I got lucky.

[@hondaxl250k0]

@@darkhorseautoanddiesel ok thanks man think you saved my vacation.. I’ve been stressing and not able to just enjoy myself 👍🏻🇺🇸👍🏻

[@darkhorseautoanddiesel]

@@hondaxl250k0 You're welcome. Granted, I can't guarantee that this will work well for you, but based on my experience and knowledge, you should be fine. Enjoy your vacation!

[@robertcheung3063]

I think you would get mixing of oil and coolant if your injector cups are leaking also.

[@darkhorseautoanddiesel]

While that technically *could* happen, it'd be very hard to do and therefore extremely unlikely. I've never seen it happen. Typically a bad cup results in fuel in the coolant. In my case it was definitely the oil cooler.

[@derrekallen2089]

So if u just have a slight oil ring in your coolant reservoir do u think it's just the oil cooler?

[@darkhorseautoanddiesel]

@@derrekallen2089 I can't answer that with certainty, but I will say, probably. On a relatively stock engines, 7.3s have a VERY low rate of head gasket failure. While it's not impossible, it's not likely. Not that it's an easy 5 minute job, but it's significantly easier to reseal or replace the oil cooler than it is to replace head gaskets, and given that, I'd reseal or replace the oil cooler first and see if it fixes it. Ideally one would check the coolant system for combustion gasses with the proper tools first, then go from there, but in some areas those can be difficult to find, and considering the age of these trucks, if the oil cooler has never been off before it's probably about to need resealed anyway.

[@MrJared0099]

Just a question I accidentally tuned my oil temp pressure port bolt what will happen

[@darkhorseautoanddiesel]

The brass plug on the filter side end cap? Oh man... the whole engine is a write off now.... Just kidding. Just snug it back and and run it. The worst thing that could happen is that it seeps a little oil, but that's HIGHLY unlikely. Even if it did, it's a 7.3, you wouldn't notice it amongst the other leaks and grease all over it haha. If it makes you feel better you could pull it all the way out, put some new thread sealer on it, then reinstall it, but you'd probably just be wasting your time.

[@MrJared0099]

@@darkhorseautoanddiesel does it need to be a certain amount of turns or something special

[@darkhorseautoanddiesel]

@@MrJared0099 Just pretty snug is good. There is torque specs for NPT fittings, I just don't recall what it is. Should be 1/8" NPT I think. Don't put the hulk on it because NPT threads are tapered which could split the aluminum housing, but tight enough it won't leak. I just go by feel, then say, "that's not gonna leak." The last step is important.

[@MrJared0099]

@@darkhorseautoanddiesel just a question a mechanic told me that adjusts oil pressure is that true

[@darkhorseautoanddiesel]

@@MrJared0099 We're still talking about the brass plug on the outside of the oil cooler end cap right? I mean, it CAN adjust oil pressure, in that, if you completely remove it, the oil pressure IN the engine will have a reduction because a great deal of it will be rerouted to OUTSIDE of the engine in the form of a horizontal geyser until the cank case empties, at which point you will have zero oil pressure, but then the engine will shut down because the injectors use oil to fire. Please don't ever take anything to that "mechanic" ever again.

[@upsidedown1972]

I am sorry to laugh about the stuff like the little oil container getting knocked off. Because I do that exact same thing. All the time.

[@darkhorseautoanddiesel]

🤣🤣🤣 I left that in the video for a reason! I wanna say I did the same exact thing on my turbo rebuild video. Now I have to go look. 🤣

[@darkhorseautoanddiesel]

I must have not left it in that video, I just looked. 😂

[@Nico090v]

Got a good chuckle out of that as well 😅

[@rubenguerrajr5833]

hello, do you clean the inside of the engine cooler pipe or just the outside? What did you use to clean the outside of the engine cooler tube?

[@darkhorseautoanddiesel]

You mean the oil cooler? I didn't clean it, I bought a new one because mine was leaking internally. If I am reusing one, I just use brake cleaner to clean up the sealing areas. I don't clean anywhere else, there's no point unless you plan on painting the outside, then clean that. I'll drain them out but that's it as far as cleaning the inside.

[@rubenguerrajr5833]

@@darkhorseautoanddiesel Thank you

[@darkhorseautoanddiesel]

​@@rubenguerrajr5833You're welcome

[@brentrlarson4153]

You'll get a new one when you order and gaskets should come with it

[@brentrlarson4153]

​@@darkhorseautoanddieselthanks every winter I get the drips which makes a mess under the truck so I broke down and ordered my set I'm glad to find your video that helps me out wondered about draining all the oil just changed it might wait till next oil change. But I don't want the muck you had better go ahead and just do it thx again

[@joeNicholson-js8ly]

Did this fix your mixing issue?

[@darkhorseautoanddiesel]

Yes it did. I've put somewhere around 50k miles on it since I made this video and all is still well.

[@ricardoduran1740]

You mentioned head gaskets as well how do I test them to make sure they are leaking?

[@VictorTransportLlc]

thanks for video.

[@darkhorseautoanddiesel]

Glad you found it helpful! I've got more 7.3 content coming soon.

[@atv55803]

great vid

[@miguelmendez4690]

I, send my like 👍🏼 tang’s from NJ

[@uhwoody]

"Three tooth ratchet"... rolling because it's true! 😂

[@darkhorseautoanddiesel]

That's what I get for having pretty much the cheapest torque wrench possible! It is accurate though, I will give it that.

[@joshbent653]

Ive done this job it sucks balls that cooker looks new

[@FernandoDiaz-ip1df]

Do I have to do the pressure test ?.

[@FernandoDiaz-ip1df]

Thank you for all your help

[@darkhorseautoanddiesel]

Not really. You can if it makes you feel better but if there's no signs of mixing I wouldn't go out of my way to do it. If you happen to have the stuff laying around in the shop it wouldn't be a bad idea just for piece of mind, but the OEM ones rarely leak internally. This was the first one I've personally seen leak internally, and it was aftermarket. You're welcome. Helping people is the main reason I started this channel.

[@carl2591]

you not flushing the block out?? leave the back coolant plug out and just run water through the system.. both sides if you can get them out.. how about mixing a bit of degreaser in water and run that through..

[@darkhorseautoanddiesel]

I didn't need to. I let it drip out for several days, and the little bit that was left in the system floats to the top of the reservoir, so I'd use a suction gun and draw it off when there was enough to justify the minimal effort. After a few months there was nothing left to draw off. I haven't seen a trace of oil in the reservoir in many months.

[@dustinnoland917]

How long did it take you?

[@darkhorseautoanddiesel]

About 2 weeks and 3 days. To be fair, I had to wait about 2 weeks for the new oil cooler to come in, and I didn't work in a manner than anyone in their right might would consider urgent. If one needed it done quickly, as long as you have all the parts and materials on hand, I would say that even with very little experience a person could have this job done in under 4 hours pretty easily.

[@darrentylor5473]

My entire engine is wet front to back top to bottom... Valley was full of more oil sand than Alberta...

[@darkhorseautoanddiesel]

🤣🤣🤣 Sounds like you have some turbo and hpop leakage going on too!

[@Buttfuker3000]

Bellhousing on trans looks cracked

[@darkhorseautoanddiesel]

I had to watch the video to see what you were talking about. I now see what you mean. It's not cracked though, not sure why it looked like that in the video. Still running the same trans over a year later.

[@azfordzilla]

Mishimito 190.00 out the door

[@Bmxr1991]

Help

[@darkhorseautoanddiesel]

Help has arrived. Unfortunately, the help isn't sure what the problem is.

[@Bmxr1991]

@@darkhorseautoanddiesel 7.3 oil cooler, I have removed the old one and cleaned the surfaces, there is pitting in the metal on the block side and filter head/ manifold. Not sure if I should run it or do something about it

[@darkhorseautoanddiesel]

​@@Bmxr1991depends on how bad the pitting is. Mine was pitted, as you may have seen in the video, I put some silicone in the pitted area and still running it to this day. If it's not horrible, you can probably do the same.

[@Bmxr1991]

@@darkhorseautoanddiesel so maybe just add a thin layer of etc to each side?

[@darkhorseautoanddiesel]

@@Bmxr1991 A very thin layer, yes. Like, just enough to cover the surface. That's also assuming the pitting isn't horrible. Without actually seeing it I can't say for sure if it's gonna work for you. If it's similar to what mine was in the video you should be fine, I'm still running mine with no issues.

[@fordnut4914]

If water is mixed into the oil will it stop the injectors from firing ?

[@darkhorseautoanddiesel]

No, unless there is so much in there that the rest of the engine is likely trashed too.

[@JaredWilliams-y3k]

When you replace the oil cooler how do y’all flush the jackets in the block and do you recommend replacing the cooler before you flush it?