Temp Gauge Flucuates???

[2.3LRNGR]

Hi i have own a 1999 ford ranger 4.0L and my temp will sometimes go from cold to normal then all the way too hot then back down to normal and so on...what does this mean????

 

[martin]

A sticky thermostat will cause that.

 

[2.3LRNGR]

Ok should i change my thermostat and then change my radiator fluid...Will this fix my problem??

 

[RonD]

How is the heat inside the truck?
Is it as hot as before or has it gotten cooler over the years?
Could also just be low coolant level, if you get air in the system temp gauge can go up and down as the air pocket creates hot spots.

My '94 4.0l was doing the up and down temp gauge thing, I changed the t-stat no help.
Came to find out the heater core is part of the cooling system, unlike most vehicles that have a temp control valve on the heater hose, this one doesn't.
So on this system if heater core gets clogged up, doesn't need to be completely blocked just partially clogged, it effects the engine cooling.
On the plus side the core was only $28 and only took 15-20min to swap out, just 4 screws.
Temp gauge is back to normal.

I would check if the heater hoses run directly into the firewall(heater core) with no heat control valve seen.
If they do warm up the engine, have heater set to cold and fan off, feel both hoses at the firewall, one will be HOT that's the IN hose, the other hose should be almost as HOT, that's the OUT hose, if it is only luke warm or cold then core is partially or fully blocked.


A failing fan clutch can cause temp gauge to go up when engine is under load, driving around, engine will be fine, temp wise, at idle but will get hot when driving.

Worse case scenario for up and down temp gauge is a cracked head or blown head gasket, this problem pushes air into the cooling system which creates hot spots until it comes out via the overflow.
With engine cold, remove rad cap and start engine, watch rad cap opening for bubbles or if it starts to overflow that could be a sign of air(exhaust) being pushed into the cooling system and displacing the coolant.
A cold cooling system has no pressure, the water pump just circulates coolant it doesn't generate any pressure or bubbles.
So if you see a continuing stream of bubbles as engine warms up you could have a cylinder leak into the cooling system.

 

[2.3LRNGR]

ok well my heat in my truck has been working normally but once in a while the heat wont be as warm as it should be man what should i check out first??

 

[RonD]

Fan clutch is easiest, open hood and start engine, you should hear fan noise then it should get quieter, shut off engine, spin fan manually it should spin freely/easily.
Go drive the truck for the day, when you get home, engine warmed up, shut off the engine and pop the hood, spin the fan again, it should be tight, won't easily spin.
If this tests out then fan clutch is good.
If fan spins easily with engine/rad warmed up then replace it.

While the hood is open follow the heater hoses to the firewall there should be a valve or by-pass on the hoses.
A Valve will have an IN and OUT on one hose, the other hose will just run directly to the firewall heater core connection.
This type of set up usually can not cause the over heating you described, because the heater core is not part of the cooling system, i.e. the engine doesn't rely on coolant passing thru the core as part of the cooling, if it did then every time you closed the valve(like in the summer) the engine would over heat.


A By-pass setup will have 4 hose connections, two go to the engine and two go to the heater core, a by-pass setup is part of the cooling system.
The engine relies on coolant being circulated between the two engine hoses as part of the circulation pathway.
When you turn up the heat inside the cab the by-pass redirects flow to the core but circulation never changes in and out of the two engine hoses.
If the by-pass is restricting flow at certain "heat" settings then you would notice this as up and down temp gauge.
Since engine is warm already feel both engine hoses near the by-pass they should be the same temp, if one is cooler than the other you could have a blockage/restriction.

If there is no Valve or By-pass then heater core is part of the cooling system, feel both hoses at the firewall they should be the same temp if one is cooler then core could have blockage/restriction.


Last is the t-stat no real way to test this, if in doubt replace, they are cheap $15, 192-195 deg is what you want, WITH a "jiggle valve", yes that is a real thing, it is a hole in the t-stat plate that allows air out of the system when refilling, t-stat should be installed with jiggle valve at 12:00 position for best air release.
The hole has a metal pin in it that "jiggles" so hole can't be clogged over time.
A 160 or 180deg t-stat will cause your MPG to go down.