2.9L Coolant Temp

Hey what are the expected operating temps for the 2.9L?

I install a mechanical gauge in my moms Bronco II, because she was say its was always sitting at the top of the dash gauge. its a 1988 auto 4x4 sitting on 31's, new thermostat, 4.0L radiator.
Its seems to get to 205* in just a few blocks and just sits there. running the heater on full does not change the temp more than 3*

I can tell the stat is opening up it takes a dip to 190 and then back up too 205 and does not dip again.
To me it seems to be running a lot hotter than other 2.9L i have owned.

205degF is fine.

t-stat should be a 190 to 195degF, this sets minimum operating temp, normal temp should be above this.

Best mileage and lubrication for a gas engine happens between 200-220degF.
All oil weight is tested/rated at 212degF, so 30w is 30w at 212degF

The faster it warms up to 200degF the better, that's what the t-stat is for, this saves you money in fuel costs.

Generally the dashboard gauge would run just below 1/2 at 205degF.
Driving up a long grade, or pulling a trailer, might get it up to 225degF, which is why the cooling system is pressurized, so coolant won't boil at 212degF, so going above 212degF is expected as part of normal operations or we wouldn't need pressurized rad caps.

50/50 Coolant mix actually boils at a higher temp than water, around 225degF.

The dashboard gauge uses a "sender" unit usually near the t-stat housing, this is a 1 wire sender , not the 2-wire sensor, that one is for the computer.

To test the factory gauge and sender remove the one wire from the sender
Turn on the key
Gauge should go all the way down or all the way up.
Now ground that one wire to the engine or jumper to battery "-"
Gauge should do the reverse of above, all the way up or all the way down.

If this happens then gauge and wire are good, if gauge only moves part way or not at all the wire or gauge is the issue.

If gauge goes up and down as it should then sender is bad, replace it, BUT never use sealing tape on any one wire sender, the threads are its ground, so part of the circuit.
leave the lower threads bare so there will be a good ground.

Here is the reason i ask
Moms bronco has a electric fan and its running 100% of the time. The switch that is install is a 195 on low and 220 on high.
If I set the fan to come on at 220 only then its pegged at 230. it just seems somethings not right

My work E250 never gets over 195 and my ranger never gets over 200 with a broken fan clutch.

Yes, 230 is too high.

I assume the sensor for the e-fan is on the upper rad, so it would come on soon after t-stat opened at 195

How old is the rad?
And what did the coolant look like last time it was drained?
Any floating bits

Couple of simple tests for radiator flow:
With engine warmed up and idling, so t-stat is open, squeeze the upper rad hose then the lower rad hose, they should be about the same pressure.
If upper hose feels a lot tighter(harder) it could mean rad flow is too slow from blocked tubes or build up in the tubes.
The lower hose coolant is sucked up by the water pump, so if the flow down from the upper hose isn't free flowing the lower hose will get softer since there is not enough coolant to suck up.
If possible have someone increase RPM while feeling the hoses, if lower gets really soft to squeeze then rad should be pulled and back flushed or replaced.
Flushing it in place won't help much, you really need to reverse the flow to get out any large bits, but even that is usually a temporary measure.
With partially blocked rad flow through out the engine is slowed and you get warmer operating temp.

Next test is on warmed up engine/rad but engine is off this time, remove cowling and fan, feel the rad for cool spots, blocked tubes will stand out as much cooler than flowing tubes, a free flowing rad should have nice even temp as you run your hand across and up and down.


If coolant wasn't changed regularly, electrolysis can eat away at the water pump impeller blades, which lowers flow, it still works just not as well.

Thanks for the info, I did not think about checking the pump.
I thought it was odd that the thermometer was reading 230 when I set the fan for only high and the air seemed cool coming off.
As for history I don't really know anything about this rig. the radator looks newer, I am pretty sure thy changed the coolent when thy replaced the thermostat.
I put a cap on it a few months ago.

I'll do some more digging. Ill get my hand on the rig this weekend again.

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RonD said:

Yes, 230 is too high.

I assume the sensor for the e-fan is on the upper rad, so it would come on soon after t-stat opened at 195

The sensor for the E-fan is tapped in right at the thermostat housing

How old is the rad?

I have no idea it, but it was upgraded to a 4.0L sometime before she got it.

And what did the coolant look like last time it was drained?
Any floating bits

all Looks good there

Couple of simple tests for radiator flow:
With engine warmed up and idling, so t-stat is open, squeeze the upper rad hose then the lower rad hose, they should be about the same pressure.
If upper hose feels a lot tighter(harder) it could mean rad flow is too slow from blocked tubes or build up in the tubes.
The lower hose coolant is sucked up by the water pump, so if the flow down from the upper hose isn't free flowing the lower hose will get softer since there is not enough coolant to suck up.
If possible have someone increase RPM while feeling the hoses, if lower gets really soft to squeeze then rad should be pulled and back flushed or replaced.
Flushing it in place won't help much, you really need to reverse the flow to get out any large bits, but even that is usually a temporary measure.
With partially blocked rad flow through out the engine is slowed and you get warmer operating temp.

I forgot to see if the hoses were soft or hard, I do that tomorrow. but with cap off at idle i cant tell if the water is moving or now. if I rev it up a bit the water level drops and i can really see the water move.

Next test is on warmed up engine/rad but engine is off this time, remove cowling and fan, feel the rad for cool spots, blocked tubes will stand out as much cooler than flowing tubes, a free flowing rad should have nice even temp as you run your hand across and up and down.

No cold spots, that i can feel


If coolant wasn't changed regularly, electrolysis can eat away at the water pump impeller blades, which lowers flow, it still works just not as well.

Click to expand...

I did do block test for exhaust gases it came back positive, so i head the heads checked no cracks but were warped. I got done with that over the weekend and its sill running hot.
I am starting to think i should swap radiator with my truck and see what happens. besides that I have no idea were to go from here.

An old time rad test:

Remove rad from vehicle
Put rad cap on
Stand rad up so the cooling tubes are vertical(up and down)
On the ranger they used cross-flow rads so rad will be on it's side

Put hand over lower hose opening
use garden hose to fill rad using upper hose opening
once full remove garden hose

remove lower hand
rad should empty almost immediately, slow flow mean clogs
Tip rad forward to empty it

Now the test.....
Flip rad upside down
if ANY water comes out it could only come from blocked tubes, the more water the more blockages.