Hello all,

I'm new to the forum. Was hoping to leverage some expertise here in helping me diagnose a cooling system issue with my 1996 4.0L V6 with 196K miles. The temperature gauge is fluctuating between [C |---X---------| H]
and [C |---------X---| H]. Ive done some searching and Ive not seen any discussion where the fluctuations are approaching the hot end. Ive only seen discussion where its between "normal" and "cold". The coolant level is topped off. Thanks in advance for you help!

 

On my '94 Ranger 4.0l I had a random temp increase and decrease.
After initial warm up I could be driving along, not uphill or down hill just cruising and gauge would go from it's "normal" spot up above 1/2 almost 3/4.
Then it would drop back to "normal"
I could be slowing down and it would do it, or driving uphill, it would go up and then drop back down even before I got to the top of the hill, totally random.

It turn out to be the heater core, on my year(not sure on '96) the heater core is part of the coolant bypass system, so there is no heat control valve on the heater hoses, coolant is always flowing thru the heater core.
Look at your heater hoses if they run from the firewall to the intake and water pump without a valve then '96 is the same as '94 setup.
Core had gotten clogged up over the years, I still got heat out but I have to say it wasn't super hot, defrost worked so never gave it much thought, lol.

New core was $28, very easy to replace, two hose clamps(on hoses) and 4 screws(under glove box), took 30mins., could do in 15 now, lol.

If your heating up happens only when stopped then fan clutch is most likely issue.
If heating up only happens under load(going uphill) then low coolant or water pump issue.

If it is random...............check the heater core
I know on some years/models they used a bypass valve on the heater hoses, this could show the same symptom if it was failing.

Hope '96 is not like the '98, seen here: http://www.therangerstation.com/Maga...eplacement.htm

 

Thanks for the info. I will look into it. Mine is totally random. It does however, seem to creep a little higher in temp when driving but fluctuates when stopped as well.

 

Jeez. Looks like I gotta pull my whole friggin dash out to get to the core. Does anyone know any definitive tests I can do to be sure that is the problem? I'd hate to go through all of this and it turn out not to correct the issue. If I do end up dropping the dash, what else should I replace while in there?

 

First, the next time you drive the truck and get home pop the hood and feel both heater hoses at the firewall, the warmer hose is the IN hose, cooler one the OUT
After engine cools down.
Drain out some coolant and remove the heater hoses at the engine end.
Point the IN hose down at the ground, or into a bucket.
Turn on garden hose, low pressure, and hold it against the end of the OUT hose.
This is called Back Flushing, it will push out any larger debris the way it came in.
Watch the flow coming out, if you start to get pressure building up at the garden hose then core is probably clogged a bit.
If flow is good increase garden hose flow, to flush out as much as possible.
If you have good flow then heater core is not your problem.

If flow is not good, stop running water thru core, use some air pressure(your mouth works) to blow water out of core.
Get some CLR and mix it with hot/warm water, pour it into the heater hose to fill up the core and let it sit for 20min.
Back flush again
Repeat as you see fit or until you get good flow.



If temp rises when stopped at a light then check fan clutch.
Start engine cold, you should hear the fan pulling air because clutch fluid is cold.
After 30 seconds or so the fan noise should change, get quieter as clutch fluid is warm and radiator is cold, so fan is disengaged because it is not needed.
Shut off engine pop hood and spin the fan, it should spin easily.
After driving to work or at least 15 min., shut off engine, pop hood and test fan again, should be tighter, not easy to spin.
If it is still easy to spin replace fan clutch.

Fan clutch works by radiator heat, on the front of the clutch(right next to the rad fins) is a bi-metal spring, as this spring heats up it closes a valve that restricts the flow of fluid in the clutch, this causes the fan to spin closer and closer to engine RPMs, so it is pulling more air thru rad and over the engine.
If this doesn't happen then when you stop no air is going thru the rad to cool the engine, so temp rises, when you start moving again air flow returns and temp drops.

 

Thanks Ron. I just remembered I have one of those Prestone radiator flush kits installed. I'm pretty sure the hose adapter is on one of those heater hoses. Hopefully I installed it on the outlet side. I'll try the flush and see if that helps.

 

Ok so when I got home from work tonight I cranked the truck (didn't drive it to work so it was completely cold) and let it idle in the driveway for 30 minutes. The gauge leveled off at roughly 25% above cold and was perfectly stable. Then I drove it out of the neighborhood. By the time I got to the main highway (roughly 1 mile) the gauge temp started to creep up to 50%. After a few highway miles it was swinging between 25% and 75% as usual. When I got back home, I let it idle again in the driveway and the gauge steadied out at 50%. Dead steady. Then I revved the engine a few times and the temp dropped to 25%, then creeped back up to 50%. So my statement above about the swing being totally random was incorrect. It fluctuates when the truck is being driven, or when the truck is not moving but the engine is being revved.

So the above results should more or less rule out the fan clutch? I still need to manually rotate the fan when hot and cold to test but Im pretty sure the clutch is ok. The heater is really cranking out a ton of heat. Especially when driving. So is it likely a faulty water pump then? It's a mechanical pump, so I don't see how it could be partially bad? I would think it would be totally dead or totally working.

 

When you rev the engine when stopped the water pump spins faster, so more circulation and temp should drop......IF it was high.
If thermostat is working, after 5-10 min., the temp gauge should show just below 1/2, 1/4 seems a bit low to me, Ford gauge has approx. 210degF as center line.
Engine should warm up to 195-200degF that's normal, 195degF thermostat is factory, so gauge just below 1/2, above a 1/3.
When a load is applied to the engine, i.e. heavy load or driving up a hill, temp may go up to 1/2 or just above 1/2, that is normal as well, 195-230degF is "normal" range for a gas engine, depending on the load.

If your thermostat is stuck 1/2 way open that would cause the 1/4 temp on the gauge, because coolant is always flowing thru rad, and when under load the stuck t-stat isn't opening all the way allowing full cooling.
Upper rad hose should stay cold at radiator end until engine temp gauge gets up to 1/3 at least, that's when t-stat should start to open and allow some coolant to flow thru rad.
So feel this hose after cold start, if it is warming up with the engine the t-stat is stuck open.

I would check the fan blade spin