Explain my radiator, please

[jstephens2]

I have a 1986 Jeep J20, my radiator cracked and dumped most of the fluid out. I plan on trying to replace the radiator myself, it looks simple but I'm not clear on how the transmission cooler works with the radiator.

My radiator has the two big hoses the circulate the engine coolant. Then there are two little hoses that I traced back to the transmission and flow through another radiator on the truck front next to the grill. I'm looking to buy a radiator from Advanced Auto Part No. 433581, it is supposed to be an exact fit.

the part I don't understand.
Is the same engine coolant also running through the transmission? that doesn't sound right to me.

[ghcoe]

Transmission oil run through those lines. There is a heat exchanger in the bottom of the radiator that the trans fluid runs through to cool the fluid down. This works fine for normal driving. When towing the trans fluid gets real hot so extra cooling is desired. A trans cooler is added to supply extra cooling. It looks like a mini radiator and is plumbed inline with the trans cooling lines.

[jstephens2]

Thanks for that answer, That make a lot of sense.
for my casual 7 mile a week drive, will the CARQUEST radiator from advanced auto be fine? or Should I look for something else?

[derf]

Yep. It's basically a radiator inside the radiator. The transmission pumps tranny fluid through the lines to cool it down.

The little radiator in the front is the auxiliary trans cooler. It gives you extra cooling so that when you're towing a heavy load, the transmission doesn't over heat. For just driving around you don't necessarily need the auxiliary cooler but it doesn't hurt.

It's always a good idea to replace all the hoses while you have the system apart and drained. The two hoses from the engine to the radiator and the one little hose from the water pump to the thermostat housing are made to fit. Most parts stores have them in stock or can get them in a day. The heater hoses and transmission cooler hoses are just regular hose. Buy enough length to fit and you're good to go. Though getting to the water pump side of the one heater hose can be "challenging" without taking a few things apart. Still, it's a good idea to do it regardless.

Oh, and it's also a good idea to replace all the hose clamps too, especially if you're cutting off the crimp clamps.

[REDONE]

For a long time folks had nothing good to say about the aluminum core/ plastic tank radiators. These days they are the norm for new cars and those that have been running them in their FSJs seem to be pleased on the whole. I think you'll be fine with a parts store radiator.

[jstephens2]

thanks for the help,
this is the exact information I was needing

[derf]

Once you have it all back together, fire it up and go through the proper procedure to check the fluid level in the transmission. (If you don't have it, the Haynes manual is actually useful for the FSJ). Swapping out the coolers loses you a quart or more.

I also forgot, it's never a bad idea to replace the thermostat. They're cheap and readily available at most parts stores. No better time than when the system is already drained. Some people will drill a 1/8" hole in the thermostat (the flat sheet metal part) to aid in getting air out of the system. I do it, but others don't and don't have any problems.

To purge air from the coolant, leave the radiator cap off and run the engine once it's all back together. Parking nose uphill is a good idea if it's convenient but avoid being nose down. Let it get up to temperature. You'll know when it does because the thermostat will open, water will start moving in the radiator and the level will drop (because of the air coming out of the block to the radiator). Pour in more coolant (which should all be a 50/50 mix) but don't keep it 100% full. Let it run for a bit and keep adding as the level drops, until you get no more noticeable drop. Shouldn't take more than a handful of minutes. Then shut it off, let it cool down, top off the radiator, and put the cap back on. Fill the overflow bottle to the correct level. After you drive it around for a week or two, double check the radiator and overflow bottle. Add as necessary.

[Cheapthrills]

Food for thought.... if I where putting a plastic tank radiator in mine I would bypass the intank trans cooler and put a bigger auxiliary trans cooler..... as it is a common issue in many newer vehicles the radiator fails internally and dumps coolant into the transmission and then the transmission is cooked...
But that's just me. I've seen it many times in the shop I tend to hang out at...

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[Nikkormat]

Food for thought.... if I where putting a plastic tank radiator in mine I would bypass the intank trans cooler and put a bigger auxiliary trans cooler..... as it is a common issue in many newer vehicles the radiator fails internally and dumps coolant into the transmission and then the transmission is cooked...
But that's just me. I've seen it many times in the shop I tend to hang out at...

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The same thing happens with brass radiators too you know.

I wish I had taken pictures but after I had a fan eat a plastic tank FSJ radiator I dissected the dead rad. The tanks were 1/8" thick glass fiber reinforced nylon and the transmission cooler was a skookum unit. Aluminum and brazed together. The tank orings were nice and beefy too, Buna N (obviously HNBR for coolant) of a fairly hard durometer so it shouldn't​ loose it's shape/sealing abilities for the next ten+ years.

It is only one core, however it is a 1 inch core. Compared to a brass radiator you'd need a 4 core to come close. Less fin density but being aluminum and a bare unpainted surface makes up for it if you ask me.

[jstephens2]

Once you have it all back together, fire it up and go through the proper procedure to check the fluid level in the transmission. (If you don't have it, the Haynes manual is actually useful for the FSJ). Swapping out the coolers loses you a quart or more.

I also forgot, it's never a bad idea to replace the thermostat. They're cheap and readily available at most parts stores. No better time than when the system is already drained. Some people will drill a 1/8" hole in the thermostat (the flat sheet metal part) to aid in getting air out of the system. I do it, but others don't and don't have any problems.

To purge air from the coolant, leave the radiator cap off and run the engine once it's all back together. Parking nose uphill is a good idea if it's convenient but avoid being nose down. Let it get up to temperature. You'll know when it does because the thermostat will open, water will start moving in the radiator and the level will drop (because of the air coming out of the block to the radiator). Pour in more coolant (which should all be a 50/50 mix) but don't keep it 100% full. Let it run for a bit and keep adding as the level drops, until you get no more noticeable drop. Shouldn't take more than a handful of minutes. Then shut it off, let it cool down, top off the radiator, and put the cap back on. Fill the overflow bottle to the correct level. After you drive it around for a week or two, double check the radiator and overflow bottle. Add as necessary.

Thanks for the information, I'm going to proceed as you advised. The thermostat is a cheap part, but being new at this, where is the thermostat on the J20?

[REDONE]

The thermostat is in the water neck. Follow the upper radiator hose back to the engine. The thing the hose is clamped to is held down by two bolts. Remove those two bolts to access the thermostat.

[derf]

Thanks for the information, I'm going to proceed as you advised. The thermostat is a cheap part, but being new at this, where is the thermostat on the J20?

Follow the upper radiator hose back to this part on the top front of the engine:



Take the two bolts off and you should be able to pop it off. It may be a little sticky, especially if it was sealed with RTV.

Once it's off, you'll see the thermostat sitting there (or stuck to the bottom of the part you take off).

Clean up the mating surfaces, drop the new thermostat in place, and seal it back up. I always use a thin smear of RTV rather than the paper gaskets but some people use the paper gaskets without problem.

Here is a picture of where you should be looking.



The upper radiator hose and the smaller bypass hose are right there next to the distributor cap (which is a TFI conversion setup). The housing is behind the hoses where it's hard to see. Once you take those two hoses off, you'll have no problem getting to it.

And, of course, remember to swap in new hoses as long as you have everything apart.

[musicmaster]

I have a radiator ill sell for $50

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