97 4.0L heat drops and temp gauge drops and rises NO HEAT

[ajparry89]

Hello all,
I have a 1997 4.0L, a few months ago i started having this issue where the temp would suddenly drop to almost the C on the gauge, then slowly rise again. when this happens i lose my heat out the vents as well. so i replaced the thermostat. I also noticed a leak in the radiator so I replaced that as the same time. that didnt seem to make a difference. then i noticed that my hoses were collapsing on themselves, so I replaced the cap and the hoses, and when I did that I noticed the water pump was leaking. when I was changing the water pump, the fan clutch was completely seized, so got a new one of those as well. after all of this, still nothing changed about my issue. I seem to have relatively poor heat, in general. but radiator is full, and i check it cold often. every few minutes now of driving, the gauge will drop way down to almost C and I also lose whatever heat i had. any Ideas what could cause this? Thank you guys for all your help!

 

[vroomzoomboom]

you either have a air pocket or blown head gasket is my guess. the first thing i would do is get a pressure gage and see if it holds or drops

 

[974X4BLACKSPORT]

Check that the vacuum operated heater control valve is opening properly, hooked up properly, and not leaking.

 

[EB4X]

There's also a die test to see if there's hydrocarbons in your coolant -- head gasket or cracked head.
If so get some K-seal for now!

 

[ajparry89]

I had thought about checking that valve next. if its not any good, i thought about just eliminating it and splicing the hoses together, for the rest of winter at least, to see if that gets me any better heat. I will pressure check next, and also look into the hydrocarbons tester thingy. these available at auto parts stores?

 

[EB4X]

I had thought about checking that valve next. if its not any good, i thought about just eliminating it and splicing the hoses together, for the rest of winter at least, to see if that gets me any better heat. I will pressure check next, and also look into the hydrocarbons tester thingy. these available at auto parts stores?

YES.... Autozone "leases" them out for free.....you pay for whole unit in advance and then get full refund upon returning....you do have the buy the liquid that changes color when detection present ...$10 --- SEE LINK

https://www.autozone.com/loan-a-tools/loaner-pressure-tester-adapters/oemtools-combustion-leak-detector-fluid-8oz/391381_0_0

 

[ajparry89]

I actually just ordered one off amazon the other day, should be here by monday, I will test it out and get back to you guys!

 

[ajparry89]

So i got the combustion gas tester tool, no matter how much i ran it and tested it, it never seemed to change any color, so possibly head gaskets are good. heat keeps rising and sinking though. I checked the heater valve, pulled all the hoses off, and it seems to be working fine internally. honestly I did not check to see if the vacuum was working..in default position its set to allow for heat so I just hooked it back up and let it be for now. when I bleed the air out using a coolant bleeder funnel, there always seems to come a point when suddenly the coolant wants to suddenly rise drastically and spill out everywhere - when i then shut the car down, let it cool and level go down, and fill up the radiator the rest of the way and start again. and usually same thing happens. I then vacuum bled the system, but i noticed something that i thought was strange..the heater hoses - either before or after the heater valve - never collapsed under a vacuum. these hoses as well should collapse just like the rad hoses, correct? what could cause that? Also, when I disconnected the heater hoses, virtually no coolant came out of them. Any ideas what this could be? are the lines plugged somewhere, somehow? NOTE: i can see my lower manifold gaskets leaking some..if they were totally shot internally, could they cause clogs?

Question: the heater hose that comes off the top/front of the lower intake manifold (right next to the upper rad hose/thermostat outlet) is the hose that feeds hot water to the heater core, correct?

Thanks for the help!

 

[ajparry89]

Yes 4.0L OHV. has the 4-port heater valve. the hoses get warm, but def not hot like they should be. what would you like pictures of?

 

[EB4X]

Here's a pic for referencing ...in case might come in handy.... 4.0 OHV

 

[ajparry89]

yes the hose that I am inquiring about is the one that goes into the very bottom of the 4-port valve - the one in the picture on the right...is this the hose that feeds hot water to the heater core?

This is really just a secondary question though. I am first wondering why all of those heater hoses did not collapse when i vacuumed it. they should collapse, correct? and when i disconnected them virtually no coolant came out. so coolant is not flowing that way apparently? any ideas on what to try or check next? Thanks guys!

 

[Mbrooks420]

Positive you don’t have an air bubble?

 

[ajparry89]

No I am not positive. But I have been at this for days. driving, idling, driving idle, bleeding, driving, idling, vacuum bleeding it, etc. there is definitly air in it still, because when i disconnect those heater hoses, nothing comes out! haha! but why wont anything go into them?? haha. nor will they vacuum down under vacuum pressure. weird. Guess i thought of trying disconnected the heater hose, running it and seeing if coolant comes out

 

[Mbrooks420]

Is the core clogged? Jack the truck up as high as you can so the heater core is lower than when it’s level. Until you get all the air out, you’ll never have proper heat.

 

[ajparry89]

I have tried with it jacked up as well, as high as my jack stand can get it, still no change..ughh. I totally understand air will cause heat issues. but I just can figure out why the air wont come out, if it is air? and in my experience (ive done some work on cars quite a bit) air in the system will also cause over heating. i never once get over heating. but instead, I get this weird symptom like clock work...every few minutes, the temp gauge drops down to almost the C, and then slowly rises back up to normal. and if i rev it for a while, eventually, suddenly, the coolant will rise all the way out of my bleeder funnel and spill everywhere - which is really starting to get annoying lol. But I think, Ok, air is coming out now...but there never seems to be a change. and when it rises, I dont see any air bubbles coming out either, just the coolant level rising and overflowing. ill shut the car off, the level quickly drops back down, I top her off again, and repeat the whole thing haha. REMINDER: If i have an air problem now, keep in mind I had the temperature dropping problem way before I had done any work on the engine or replaced anything.

 

[Mbrooks420]

The coolant temperature sensor won’t read Awwww correctly if it’s completely flooded. Try jacking up the passenger side, and blowing air through the heater core to make sure it’s not clogged.

 

[ajparry89]

If my heater core is clogged, that will cause the temperature gauge to drop and rise like clock work?

 

[Mbrooks420]

It’d be an incomplete circuit, so it might allow trapped air, which can mess with the temp gauges function.

 

[ajparry89]

heater core not clogged