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swebster 08-27-2003 04:22 PM

Oil Cooler Lines
Does anyone have a source, part number or replacement idea for the hard oil lines that feed the oil cooler built into the radiator (86' 345)? They run under the front frame support and around the passenger side of the shroud.

I've tried NAPA and AZ but they come up with "we have brake line". This is the last "to do" before I can fire her up again.


PeterH-350LE 08-27-2003 04:35 PM

Some years ago, I replaced those lines on another MH. I went to a place that makes hydraulic pressure lines and had some custom made using my old fittings.

thenewkid64 08-27-2003 05:26 PM


That is what the guys had to do on the engine swap. The lines practically fell apart when they tried to clean them :(. I am still looking for the paperwork so I can get JPAirstream a NAPA number for the lower hose.

swebster 08-27-2003 05:52 PM

Wow, you guys are bumming me out. I should have been more careful when I removed them. So its off to the heavy equipment guys?

74Argosy24MH 08-27-2003 06:00 PM


hard oil lines that feed the oil cooler built into the radiator
That sounds like tranny cooler lines, and replacements are usually made out of brake line. Nearly every AT vehicle has them, they are all formed differently and stocking them would be a nightmare. Oil cooler lines are usually hose and larger for the flow.


59toaster 08-27-2003 06:02 PM

Look up hydraulics in the yellow pages.
Place near me called Royal Brass and hose makes that sort of stuff and it's reasonable. It's probably less expensive then going through GM. Last time I needed a specialized line they made it while I waited. I'm sure that would have been a order it an wait a week at the dealer.

PeterH-350LE 08-27-2003 06:36 PM

Re: Oil Cooler Lines

Originally posted by swebster@myrvadvanta
.... that feed the oil cooler built into the radiator (86' 345)? ......
If I would going through the trouble having new lines made, I would strongly consider taking the oil cooling out of the radiator and installing a seperate external oil cooler.
It seems that all the rigs with the cooler built into the radiator are running 20 to 30 degrees hotter????
Am I totally of base with my assumption?

swebster 08-27-2003 07:20 PM

I'm sure they are oil lines. John, you're right about the tranny lines. They're on the driver's side and look to be made from brake line. Someone installed an aftermarket trans cooler so those lines are routed into the radiator, then into the add-on cooler than back to the tran. The oil lines are in fact larger lines and come up from the rear of the engine, convert to flex below the crank pulley and then back to hard lines (bolted to the front frame support and terminate into the radiator on the pass side.

Well I guess I have a couple of options; One of my clients is a heavy equipment dealer so I could probably call a favor and get some lines made fast and cheap. But I like the idea of capping them off on the radiator and running an external oil cooler ($50 @ NAPA) as well. I would be very interested in this approach if people have seen lower coolant temps with this setup.

One thing I'm getting a little worried about is space in the nose. With two coolers and a soon to be installed condensor (mine was missing) can everything fit and not block airflow to the radiator?

87MH 08-27-2003 08:17 PM

the idea of capping them off on the radiator and running an external oil cooler....
Caution is advised here. The cheaper air/oil coolers may be too restrictive, both in oil course capacity and air flow area. Deficient oil course capacity could cause too high a delta pressure and an excessive oil velocity which would not allow enough time for sufficient heat transfer.

My 345 also has both the tranny and engine oil coolers internal to the radiator, but I really don't know what could be done to increase cooling capacity.

An efficient external air/oil/tranny fluid heat exchanger mounted in front of the radiator would certainly increase the temp of the air to the primary cooling fins. The net benefit of the added external cooling equipment may well be a wash due to the added heat load of increasing the air temp hitting the front of the radiator.

I'm not saying it shouldn't be tried, just that some accurate temp measurements in and out on all three cooling systems (water, oil, and tranny) should be monitored before and after to assess if all problems are being addressed.

Last weekend I ran into a water temp running close to 220 F indicated while doing 63 in East Central Texas. Normal cruise previously was 210 F, but at ambient air temps at least 10 degrees cooler. This would lead me to believe that the radiator is nearly maxed out, but I want to try a cooler thermostat prior to replumbing any fluid flow.

59toaster 08-27-2003 08:30 PM

My 88 Burb has a factory external oil cooler mounted infront of the radiator. I don't think the internal oil cooler is adding that much heat to the coolant. I have a temp sender in my oil pan and the oil temp AFTER it's been through the engine is only running 10-20 degrees higher then the coolant temp.

Now transmission is a whole different story. A transmission under load can put a LOT of heat into the radiator in a hurry. The Aux cooler you have is helping quite a bit. If it's as effiecent as the ones I have installed I doubt your tranny is running any hotter then the engine under normal cruise. The tranny temp gage in my other truck rarely gets above 160. I'll be installing the sender for the tranny temp this weekend so I will have a TH 400 reading soon.

thenewkid64 08-27-2003 08:50 PM

Here is my 2 cents worth.

In both of my 70"s vintage coaches I have an imbedded trans cooler that is part of the radiator. Oil is a lone cooler that mounts in front of the radiator. On the 76 I added a transmission cooler and plan to do so on the 78.

I would be willing to bet that the reason all 3 are integrated in the 80s models is cost. Cheaper to build it all in one than have 2 or 3 individual coolers.

There is a forum member who redid the sheetmetal on the front of his MH and remote mounted oil and transmission coolers with air ducting and thermostatic fans to keep it all as cool as possible. I understand the concern for air flow, do you have room to one side or the other to mount the coolers?

PeterH-350LE 08-27-2003 09:19 PM

My 79 came with a factory installed external oil cooler as well. I added the aux trans cooler. No air flow problems.
If the 3 fluid radiator was such a great idea, why did they quit using them?

swebster 08-27-2003 09:37 PM

1 Attachment(s)
Sheet metal is certainly a possibility. To be honest, I'm trying to keep this as simple as possible but certainly want to reduce operating temps and do it right the first time.

I don't think there would be much room for a side mounted trans & oil cooler as the vertical frame supports pretty much fill up the space between the grill/headlight housings and the radiator. There is plenty of room in the pass side fender well and I could see how ducting could work but this is getting beyond my current goals for this project. It certainly could be a good future project.

While most of you are very familiar with what this all looks like I've attached a pic that I took during disassembly which shows how the trans cooler is mounted to the grill. Its hard to see much else but adding an oil cooler to the other side would easily cover the entire grill and be directly within the airflow to the radiator.

One question on the trans...should I re-plumb the setup so the aux cooler is the only cooler or should I cool in the aux first then run it through the radiator?

Also, Dennis thanks for the caution on cheap oil coolers. You must be an engineer! If so I'm glad you're on our side!

swebster 08-27-2003 09:48 PM

Pic of the Lines
1 Attachment(s)
By the's a shot of the oil lines that got this started

George 08-28-2003 05:57 AM

cooling lines
Cooling lines ,either transmission.. or motor oil, operate under MUCH LESS pressure than brake lines. you are able to use brake lines as they are designed to withstand much higher operating pressure.
Now if you are wanting to replace FLEXABLE hose lines,
thay can be made by most larger napa stores,they use Hydraulic lines for this, altho I have seen people sucessfully use plain ol fuel hose on the trans cooler lines as these are low pressure.
If you plan on adding a aux. trans cooler, route the trans. oil throught the radiator cooler FIRST, to cool it down to coolant temp
(approx) than through the aux. cooler for additional cooling.

Usually trans. coolerl lines are 5/16" with inverted nut fittings
engin oil cooler lines are bigger 3/8' or maybe 7/16'
Tractor supply co. also has Hyd lines(hoses) already made up.
I think they come by the foot. also farm machinery dealers make custom hoses.
I hope this helpes.

59toaster 08-28-2003 05:59 AM

Passengerside lines are usualy transmission.

Is the ends on those lines double flare or single flare? Double flare tool is $25 at a auto parts store. Not hard to do.

Problem is you need to be on a straight section of tube. Looks like you would have to cut about 2-3 inches to get past the existing bend. Is there enough slack in the lines to get that 2-3 inches back? Don't forget to put the fitting on before you flare.

George 08-28-2003 06:11 AM

I was looking at your picture, if the lines are ok other than being twisted off, you can cut them off, and re flair them. if they are a bit short you can put in a connector and a short piece of line.
I bet you could do that for under $10.00
I should mention you will need a flairing tool ( it can be borrowed from a mechanic friend or rented from autozone or the like) get a "double Flair" kit if you can, its better
just put the fittings on the line BEFORE you flair them ( don't ask) HA, LOL.
ol' George

74Argosy24MH 08-28-2003 06:40 AM


One question on the trans...should I re-plumb the setup so the aux cooler is the only cooler or should I cool in the aux first then run it through the radiator?
If you are going to only use 1 cooler it has to be the radiator cooler. If you use both run it through the radiator first then the external cooler.

I am not a real fan of stacking coolers in front of the radiator, it slows airflow and makes it a major job to clean them. In radiator coolers for the trans are ok, but these engines run pretty warm (heavy loading, poor airflow, and a non-locking convertor) and the engine oil needs to stay outside the radiator.


PeterH-350LE 08-28-2003 06:48 AM

When I pulled my radiator and had it recored, it was a no-brainer to replace the waterpump. Considering the condition of your belts, one could reasonably assume that your waterpump is next, sooner or later.
Just something to consider ...

swebster 08-28-2003 06:51 AM

1 Attachment(s)
I'm not sure I understand the difference between a single flare and a double. The lines have what look like a "T" in the line. There is also a small rubber o-ring in the radiator. It looks like the fitting compresses the line into the o-ring.

PeterH - I'm with you all the way. I replaced the water pump while I had everything off, play in the pully, way too easy to turn, all the usual suspects.

Here's a pic:

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