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Discussion Starter #1
Hi guys, I’ve had bad heat for a few winters now. About two years I had the radiator and heater core replaced; it didn’t help the heat temp.
In the past I’ve been advised to back-flush it and check/replace the thermostat. I have some time next week and am planning on doing it, while replacing my hoses and coolant.
Does anyone have a great video showing how to back flush a 4.2? 1989 carbed if that matters?
Or, maybe take a few minutes to walk me through it?
Also, best thermostat and from where?
Thanks guys, I am hoping this does the trick.


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Make sure your cowl is cleaned out properly too and that your doors are opening and closing correctly.

 

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In addition to the above advice, I suggest a 190* MOPAR thermostat. Jon Stevens gives a link to a great explanation on the YJ heater box.
It could be that one or more of your cables need a little adjustment.

Good Luck, L.M.
 

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Discussion Starter #6 (Edited)
Sorry guys, life happens.
I haven’t done anything except make sure my cowl was clear and check my doors, everything seems fine.
Someone asked about my temperatures, so I took a few today.
The gauge reads around 190-200° when arriving to work, about a 35 minute drive.
Temps:
Bottom hose going into the firewall: 135°
Top hose 161°
Motor where the temp gauge wire connects 230°
Vent where the heat comes out in the floor was 143°
Ambient temperature was about 50-55° today.
Neither of the hoses going into the firewall were too hot to hold onto, I know I’ve read mention of that somewhere.
Is there any chance the hoses going into the firewall got reversed when they did all of the work previously?
Would that matter?
Open for any more suggestions.
If y’all still think I’d benefit from a mopar thermostat and a reverse flush, I’ll try it.


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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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143* at the vent is warm enough, I would look at increasing air volume. Possibly Tiered fan motor or vent gate for heat not closing all the way, or even something in the air box itself blocking air flow. Do you have enough air coming out the vents?
 

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I have heard that aftermarket heater cores have less tubes and don't put out as much heat and you are better off having the originals rebuilt. I have never use a chinese replacement so i don't know if it's true or not.
 

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I have heard that aftermarket heater cores have less tubes and don't put out as much heat and you are better off having the originals rebuilt. I have never use a chinese replacement so i don't know if it's true or not.
It's true. Here's a side by side.
I ended up having the original repaired because the aftermarket core fit terrible.

Good Luck, L.M.
 

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I've had good experiences with the aftermarket heater cores (two different YJs). If your engine is getting up to temp and your core isn't blocked then you should be good from that side. I agree with GIAL, 143 out of the vent should be good. Make sure your fan is moving a lot of air when it's on full. I was driving around this morning in Atlanta (38F) and once the engine was up to temp the tub was nice and toasty (pushing air down warms it up much faster :).

If you don't have an A/C, taking the blower assembly out is not that difficult and cleaning it out is a satisfying experience (4 nuts on the firewall accessible from the engine bay and the two hoses - but you'll have to drain the coolant).
 
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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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I forgot to mention the S-10 blower motor upgrade. more power, air flow, you can find out all about it from youtube. Google it
 

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Discussion Starter #14
It was cold today. Raining, then sleeting, then snowing.
I put a coat and toboggan on, and drove the old Jeep.
Left early enough to get some temps when I got to work, which is about a 35 minute drive.

Bottom hose going into the firewall 130°
Top hose 125°
Motor where the wire from my gauge attaches 259°
Vent blowing out the bottom 126°
Outside temperature was 34°
Remembering what someone had mentioned, I grabbed both hoses going into the firewall and could hold onto them with no issues.
It was not bad, but it wasn’t warm inside either.
I have no idea how hard the fan is supposed to blow, or even how to measure it, but it does seem to blow hard enough, just not hot enough.
I moved the lever from heat, to defrost and couldn’t notice a difference in the “velocity“ of the air.

Does this help diagnose anything?

I keep going back to the “you shouldn’t be able to hold onto either of the hoses (that go into the firewall) for very long” thing, because it’s simply not a problem for me.
I checked the coolant Saturday, it’s fine.


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Discussion Starter #15
I've had good experiences with the aftermarket heater cores (two different YJs). If your engine is getting up to temp and your core isn't blocked then you should be good from that side. I agree with GIAL, 143 out of the vent should be good. Make sure your fan is moving a lot of air when it's on full. I was driving around this morning in Atlanta (38F) and once the engine was up to temp the tub was nice and toasty (pushing air down warms it up much faster :).

If you don't have an A/C, taking the blower assembly out is not that difficult and cleaning it out is a satisfying experience (4 nuts on the firewall accessible from the engine bay and the two hoses - but you'll have to drain the coolant).
What does “pushing air down” mean?


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What does “pushing air down” mean?


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He is saying don't use the defroster if you don't need it, direct the air out the heater vent to the floor. Heat rises warming the entire cabin air.
 
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