Hey jeepers, happy Friday!

So my 90 xj, 4.0 5spd, has an open cooling system now. I got the rad cap off a Durango, and spliced it into the upper radiator hose. Not a perfect location, but it works. Here's my question.

The cap that is on it now is a 13psi cap, and my motor, as well as taking a reading with an ir thermometer, always shows 150 on the gauge, 160-170 on the thermometer. So here's my question, if I understand it correctly a lower pressure cap is going to allow the motor to run cooler because the coolant does not build up much pressure therefore not be as heated as it would be with a 16 psi cap. Is this a valid thought? Or is there just somethin funky going on? It doesn't leak anywhere, the overflow doesn't spew over...ideas?

 

The pressure rating on the cap only has to do with raising the boiling point not controlling the coolant temp. Since you are only reading a max of 170 deg it sounds like you don't have a thermostat in there. Should be 195-205 fully warmed up. T-stat controls the temp, so sounds like time for a new one.

 

Here's the kicker- this is the 3rd tstat that has done this. When it was a closed system it worked fine. Open system, now it over cools.

 

Where are you getting the t-stats from. Try an OEM one from the dealer. I would also verify the temp with an I.R. temp gun.

 

Been verified by ir, on hot days if it sits at idle for long enough it will hit 200, otherwise it hits 170ish

 

52028186 from the dealer only.

 

Oddball question, but easy enough to answer. Idling warm, does it cycle about every 20-30 seconds?

 

Not really, more like hits 200, just sits there till I give it some gas and it drops back to the 170 ish mark

 

My money is on a crappy stat.

 

I meant the idle speed!

 

Ahh, Uhm, now that I think about it yes, 20 or 30 secs is spot on, why may I ask?

 

The 02 sensor is dead and it's running rich. Maybe 16 MPG, tops? When a liquid, (gas in this case) "changes state", to an actual gas, heat is absorbed in the "change of state". Your AC and refrigerator use the same principal. All that gasoline evaporating could be sucking up heat.

This thread rambles, was even somewhat "sabotaged" , but right at the start is EcoMikes 02 sensor thread. > https://www.cherokeeforum.com/f2/ren...ce-rms-133153/

 

Very interesting, I myself had pondered if that was a possibility. Would backfires above 3k when I shift (going onto the interstate, for example) also indicate a rich condition?

And dead on with the mpgs, granted I'm running 35s on 3.73 gears, but I'm averaging 13-15, too much error for a good average

 

Oscam's Razor?

"Would backfires above 3k when I shift" *****I really don't know there other than extra un-burnt fuel in the pipe could defiantly ignite.

If you don't know the history of your 02 sensor, I'd say change it. Some guys here seem to buy everything new every 6 months. I'm on the other end of that scale and almost never advise anyone to buy anything. You will eventually get your $70 back in fuel savings, and maybe your heat also.

 

Fair enough, yea the backfire thing I don't know, but everytime if it goes over 3 in acceleration, a nice bang out the backside happens. Also, aren't you the one who used the Volvo injectors in the renix? If so, I'm using those as well, very nice upgrade.

Anyways, yes I'm a broke kid as well, so when Friday comes around I'll try to snag one online for cheap, any preference of Bosch/ntk?