Using the trans radiator heat exchanger for engine oil cooling?

[Chris_North]

Short and sweet:

Has anyone ever used the trans heat exchanger in the radiator to cool engine oil? I didn't search these forums admittedly but I did some google searching and the best I could come up with is 60% of people saying it's a bad idea the rad exchanger isn't meant for those pressures or volumes and 30% of people disagreeing and saying it's fine. But nobody actually seems to have done it. I've read that there are some models of cars/trucks that have an oil cooler setup through the radiator built in from the factory, but that's I'm sure something they engineered for that purpose, not repurposed something for something else.


Long version:

It occurred to me today that the trans fluid coming from the transmission going to the radiator cooler rarely makes it above 190F in my truck (and not too often does it see that unless I'm hauling or it's hot out). The engine coolant operates between what 180F and 215F? With auxiliary coolers, isn't it counterproductive running the 170F fluid to be "cooled" by 200F fluid? TBH I don't know exactly what temps the coolant runs at but I do know my trans temps.

Over the weekend I installed a new radiator and while I was at it I decided to give one of those electric radiator fans a whirl (haha, unintentional pun). Today was my first road test with my 50 mile highway commute and 45 mile back road trip home (to avoid traffic). On the highway I noticed no difference with the e-fan over the belt one with regards to temp, but the oil pressures (which like a lot of rangers is normally low already) were running maybe 5 PSI lower than normal. I have no real way to check but my engine block seemed a little hotter than normal when I finally stopped. The hilly stop and start backroads is where I noticed the change. Oil pressure was still a good 5 PSI lower than usual, but trans temps went higher faster and stayed there longer. I run an additional cooler to the stock aux one and usually neither one gets very warm, but today when I finally got home they were both hot to the touch. Odd thing is, the in-dash coolant gauge never got above where it would be with e-fan, so I'm thinking it's down to the electric fan only moving enough air to keep the coolant at temp and only coming on as needed and not constantly moving air through the aux trans coolers and around the engine.

So basically in order to keep my trans happy with the e-fan I think I'm going to have to install a better cooler, which is okay because i was planning on it anyway. But like I said I got to thinking today with the coolant temp ideally running hotter than the trans temp, why even run it through the rad's heat exchanger at all? If that exchanger is freed up and my engine oil is (or so I assume) running hotter than ideal why not utilize the exchanger for engine oil cooling? Anyone find any flaws with my reasoning?

 

[BRUTUS_T_HOG]

The idea with an engine oil cooler is that oil can run in the 300-400 degree range so cooling down to 200 is good.

A lot of cars come factory with integral radiator engine oil coolers. I believe a lot of explorers came with a oil cooler integrated to the oil filter plumbing.

I guess it depends how you use your engine. Heavy hauling and lots of idling? Oil cooler.

Light loads and daily commuter? Why bother.

 

[adsm08]

Liquid to liquid coolers are far more efficient than liquid to air. I suspect that if you do what you propose and don't add a trans cooler that is nearly the size of your radiator you will end up overheating the trans.

 

[Chris_North]

The idea with an engine oil cooler is that oil can run in the 300-400 degree range so cooling down to 200 is good.

A lot of cars come factory with integral radiator engine oil coolers. I believe a lot of explorers came with a oil cooler integrated to the oil filter plumbing.

I guess it depends how you use your engine. Heavy hauling and lots of idling? Oil cooler.

Light loads and daily commuter? Why bother.

Wow I would have figured that to be too hot. Like I said I don't have the slightest idea what temp my oil runs at but I know that once the truck is warmed up and driven for a while in hot weather at a stop the oil pressure can dip as low as 9 PSI. I realize that's not simply because the oil is too hot, but I was thinking it was probably a factor.

Liquid to liquid coolers are far more efficient than liquid to air. I suspect that if you do what you propose and don't add a trans cooler that is nearly the size of your radiator you will end up overheating the trans.

True, but all heat needs to be carried away by air eventually. Truth be told I'm really not confident it will even work let alone work well enough to warrant doing. It's just that I noticed the trans temp rarely gets into the temperatures that the engine coolant runs at, and almost never above. My feeling is that a majority of the time the trans fluid is picking up heat from the radiator then having to dump it out the external coolers anyway (which I just realized it potentially beneficial to engine cooling), so what would be the difference? Although the trans exchanger is on the "out" side of the rad, after the coolant is cooled, so I really don't know what temp that's at either.

I don't know there's too many variables for me to just do it and too many tests needed to be done to ensure it'll be safe before I start changing stuff. I am more thinking aloud than seriously considering doing this, I am just hoping for insight and discussion.

 

[Bronco638]

This probably isn't done because engine oil typically runs hotter than engine coolant. So, now you're asking the radiator not only to remove heat from the coolant but also from the engine oil. The radiator isn't really designed for that. Granted, while towing, you're asking the radiator to do just that. However, you've noticed that your tranny oil temps are generally pretty low.

I had a '96 Explorer and added a sandwich adapter so I could use that to get a mechanical oil temperature probe into the oil stream, at the filter. You could use the same thing. Trans-Dapt makes a sandwich adapter that includes ports for an oil cooler (part # 1313). This adapter routes the oil out of the engine (to the cooler), back thru the filter and then back to the engine. The ports are 3/8”-14 NPT (National Pipe Thread). Auto Meter makes a 3/8”-14 adapter (part # 2263). Those part numbers were posted 9 years ago (LINK). So, double check those part numbers. They're for an Explorer so Ranger parts might be different.

IIRC, the First Gen. Explorers came with an oil cooler. Those should be easy enough to locate in a junk yard. Use one of those coolers, with the sandwich adapter. Then, you can leave the radiator to cool coolant and tranny fluid. Or, get a new oil cooler from Summit Racing. It's doesn't have to be very big. 50 square inches of exposed cooling fins is probably plenty. I'm pretty sure that's about the same size as the o.e. ones in the First Gen. Explorers.

 

[joescool2008]

My turbo eclipse has a oil to coolant exchanger on the oil filter housing. I think if you had a manual transmission it would be ok to use the extra lines to do oil cooling.

 

[adsm08]

One thing you have to look at is placement of temp sensors, before you go saying that the trans cooler on the rad isn't doing anything useful.

The trans temp sensor is in the pan, where the fluid goes after it comes back in from the cooler. The coolant temp sensor is usually very close to the thermostat housing, the last place the coolant is before heading out to the rad. That means you are comparing the coolest trans temp with the highest coolant temp.

Since the trans coolers are either on the side (with the return at the bottom), or run along the bottom you are getting trans fluid cooling from the coolest coolant in the system.


And yes, you are correct, all the heat has to be vented to air at some point. That is why, out of all the coolers, the radiator, the AC condenser, and the CAC, if it's there, are the biggest.

Look at a radiator compared to an auxiliary trans cooler. The radiator, that has to cool the whole system to air by itself, is huge compared to an auxiliary trans cooler.



Oh, and on an engine at operating temp at idle, 9 PSI oil pressure isn't that bad. At temp you usually want to see 10 PSI per 1000 RPM. The 5.4 is supposed to have 15 at idle, but that's because it needs a minimum 15 to run the cam phasers.

 

[Chris_North]

I don't really want to add an additional external cooler. Unless I'm going to place it in front of or behind a trans cooler or run lines remotely some place I don't think I have the room.

I have seen (in fact I thought the V8 exploders had them?) the coolant oil filter sandwich adapters.

I'm actually only going off of the stock in-dash gauge so I really don't know what the temp of the coolant is. My trans temp gauge is aftermarket and mounted a foot away from the outgoing line of the trans, so it's definitely the hottest measurable temperature of fluid. I did realize that the exchanger is vertical and on the return side of the rad so it should be getting cooled by the coolest temp coolant available, but I still don't know for sure what temp that is. I think what makes the most sense is to get a sample of temperature before (which I pretty much already have) and after the rad exchanger, or even further of each cooler, and see the efficiency of each. I might do this as it shouldn't be that hard and report back on the results. TBH I'm really just curious about the whole thing and would love to have some solid figures rather than just having to assume and guess.

Trans coolers always seem too small to me. But that's just IMHO.

I changed the oil last night and today was even hotter than yesterday but my oil was running at a slightly higher pressure than yesterday. You're right about OP adsm, I guess I'm just used to GM vehicles which always seem to run at at least 25PSI.


Either way to keep the E-fan I'm definitely going to have to either get an additional trans rad or a better one than I have, because I am definitely running way hotter than normal. Last year during similar ambient temps I would have to be pulling a trailer to reach the temps I hit unloaded the past couple days.

 

[naford]

This is kind of late. But my 02 FX4 XLT V6 auto transmission has one transmission cooler line that runs to the radiator, then from the radiator it goes to a secondary cooler on the passenger side in front of the radiator, then goes back to the transmission. The lines from the transmission are metal, but the lines going to the cooler are rubber transmission lines. I'm not sure what version Fords have this secondary cooler but if you could find one it would take care of cooling your oil. Pull a part might have one. Ford I think wants well over 100 dollars for one.