86 2.5L Cooling System

[eaglescout526]

Hey y'all.

So I have had the pleasure to work on an 86 MJ with the 2.5L with an automatic trans hooked up to the trans cooler in the radiator recently and I'm kinda stumped with the cooling system at the moment. The owner never really took great care of it from what I can tell. So I had the owner get the head checked out because he overheated it and it is fine. 

here's what I have done:

Cleaned radiator inside and out,

put a new t-stat in due to the system not having one,

Put in a new cluster along with sensors(will elaborate)

Put in a NOS water pump due to wrong rotation water pump

Cleared blockage from reservoir and cleaned it as well

 

All that isnt new is the main lower and upper hose, I have bled the air out from the temp sensor and am still reaching over heating temps which kinda scares me but here is the deal with the cluster. I have a couple 5/6 clusters for the 86 year. I compared them all and installed the best one I had. Temp gauge works as I think it should because it pegs out both directions but seems to still climb. Climbs less rapidly than yesterday as I didnt have the system burped(oops) but now it mostly is and seems to still have an issue. Now here is where it gets weird, temp gauge climbs high and it seems the t-stat doesnt open up until what seems like it is past the point of no return. I do not have a digital thermometer to see what some of the temps are. It sounds like the water is boiling definitely but not traveling through at all and the radiator remains cool.

 

I am wondering, is it the old main hoses caked with the bad crap thats failing?(lower hose has no spring in it) Air still trapped?(I didnt have this issue when I installed AC as the system is supposed to purge itself of air with the overflow) Bad radiator cap?(it is rated for 13psi but could not be holding any pressure).

 

Any thoughts? I don't want to drop in the new radiator only to still have the same problem. And I also don't want the owner to throw more money at this but it seems possible for that to happen until this is correct. 

[Green Mesa XJ]

Reservoir was clogged? Radiator could be clogged, used to be you could take a radiator out and have a shop test it and recore them if needed.

Other thought is passageways in the head and block could be blocked with gunk.

How much is money an issue? I found an Aluminum radiator on eBay for the 2.8 for like $150, I dunno it has automatic transmission cooler lines or not. But maybe a new radiator wouldn’t be a bad idea. Still could be clogged in the block or head some where stopping the coolant.


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[eaglescout526]

Reservoir was clogged. Well the main hose was that the cooling system would draw coolant from was. This radiator could be on its way out, it looks a bit underwhelming for how thin it is paired with the condenser. I felt air passing through the condenser when I was testing it and it was pulling through but I will still clean those fins. I did run vinegar through the radiator and the radiator only took half a bottle of a gallon of vinegar(which could indicate clogged pathways). I will swap radiators our for sure and this new one the owner got has the right lines for the transmission which 3rd time was the charm as the first 2 was wrong all the way around. 

 

Head was inspected and rebuilt by PHX cylinder head which I went through them when I rebuilt mine and they did a great job. I trust the job was done right and well.

[Green Mesa XJ]

On these old jeeps could be the condenser is enough to change the cooling if it’s new to the set up. 2.5 -2.8 don’t need much of a cooling system compared to the 4.0.
Only time my old2.8 xj got close to over heating it was a blown hose. Up steep terrain at high altitude in low gears engine working hard it was fine. Not fast but fine.

If the head was off I suppose the block as much as could be seen looked ok. Just leaves the radiator unless the heater core is somehow restricting the flow as well. If it was bearly working before ac was added it might be enough to cause it to over heat

Shops around here used to flow test radiators anybody still do that around you?

On the other hand the OSC 871 at rock auto doesn’t look bad for the money. I tried to buy that one from summit, rock auto didn’t have it then, waited from March until September to get it in from China. It was wrong, right box wrong radiator. The pictures on summit and rock auto look correct I think I got the wrong radiator in the correct box.
I ended up with a three row from eBay for the same money, they are out of stock now.

assuming good water passageways, new water pump, thermostat, and it’s burped, bad radiator makes sense,


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[eaglescout526]

Yeah. I just want to make sure everything is right for this guy. What’s funny but I omitted before is he has the heater core completely eliminated for whatever reason so the hose from the water pump goes right to the intake manifold. Basically bypassing the non existent heater control valve which is fine. AC system is factory to this truck and has been disconnected for a bit. I recommended to the owner to get a new condenser due being open and exposed. I really do want to put the heater back into the system but some hoses are lacking at the moment to put that back in. But swapping the radiator is planned.

 

I did examine the engine and didn’t see anything plugged up anywhere so we’re good there. Could be remnants of gunk in the system somewhere that was missed in the flushing. 
 

Supposedly the owners neighbor works on radiators and recommended to get a new radiator. Not sure if it was tested but I’m assuming this was based on a quick examination by the radiator guy. 
 

 

[cruiser54]

get an IR temp gun.

[dasbulliwagen]

I had a similar issue on mine. ended up the original radiator was clogged, even though it had been flushed and kept good coolant in it. I bought a cheap plastic tank model and it did fine for a few years, but it blew the lower tank off one night at a downtown cruise. I replaced it with a fully welded aluminum rad. I also went with a higher PSI  rad cap from a TJ and some water wetter. Every little bit helps, but I havent had an issus since.

[eaglescout526]

I’m leaning towards the radiator at this point. I still had air in the main return hose which isn’t till surprising me at the moment so I know what I need to do when refilling the system. 

[YipTheYapper]

Hi. I had a similar overheating issue on my 87 Comanche. I changed out the water pump, t-stat and temp gauge, the aftermarket temp gauge was busted and not reading at all. 
 

I installed the new temp gauge and didn’t connect it to ground, so it was slowly claiming up to 240-250 degrees. I used a temp gun on the engine, reservoir and hoses all giving me a reading of about 140-160 degrees. 
 

long story long, I checked the temperature gauge and noticed that I effed up and didn’t connect it to ground, only had the ignition and the sending unit connected. Once I connected the ground to the body, started it back up and Wham! now the temperature I was getting with the IR gun, was the same temperature as the gauge. 
 

Word to the wise- listen to crusier54. IR temp gun definitely needed. 

side note- you can also have a partial clog in the radiator. Running your temperature gun up/down and across the radiator will let you know if you have any cold spots. 

[eaglescout526]

Actually I found two issues. The original radiator was more plugged than I expected. I ran the system with fresh stuff twice and the coolant still came out brown. So I said to hell with it, swapped in a new radiator. Made the trans lines play nice with the new radiator without really messing anything up and was still having over heating issues. Except! A twist. Once it got to the 240* line, it actually fought to stay cool and I couldn’t think as to why it was doing this with having the new radiator in. Then it dawned on me. The owner or previous owner changed the hose from the intake manifold to the T-stat out with the wrong hose and it looks like the arch you would find in St. Louis. Basically how it is supposed to operate with the flow is push water through the manifold to the T-stat to open it up sooner than let the water boil in the block. Well the cooling system doesn’t create enough pressure to push the water through that U bent hose to do that. So that being the only thing at this point that isn’t factory leads me to believe this is the last issue and as I removed the hose and found little to no coolant in it and felt the hose to be quit cooler than the rest of the system. Plus it also took the t-stat a long time to open since most the air was hanging around there and not the back of the block as I tried to bleed it all out. So we shall see when the new hose comes in.