2.9 running hot after replacing air pressure sensor cap

[Cortese60]

Just bought an 88 ford ranger xlt 2.9 L 4x4 last month. Guy I had bought it from had just replaced water pump, radiator and hoses and had receipts to prove it. I replaced the spark plugs and did a synthetic oil change. Truck was good and ready to go...
Then about a week ago stalled out. Thought it might be a fuel pump but a friend who works on cars said it was the cap to the air pressure sensor. Replaced that. Then I'm driving it home and about half a mile from home it starts to overheat. Check engine light comes on and steam is coming out of the hood. Temp gauge inside truck doesn't move. Manage to get it home. All fluids were good, including oil and coolant levels. As soon as truck cools down engine light goes off. Spoke to my friend who said he didn't see anything in there and recommended changing t-stat which I will do in the morning. Cant see how it be anything related to wp, radiator or hoses since those are all new. Any other ideas?

 

[RonD]

Trying to figure out what an "air pressure sensor cap" is??


If the previous owner was having an overheating problem, the only real reason to "replaced water pump, radiator and hoses", then I would say those things did not fix the problem.

What does the coolant look like?

Not saying this is what happened just saying it does happen:
Vehicle is overheating, owner replaces cooling system parts only to find out there is a head gasket or cracked head issue that is causing the overheating.
They put a can of Head Gasket Sealant in the coolant, and run the engine as instructed, and this stuff DOES work.
You are suppose to leave this stuff in the coolant as seal can fail and new sealant will take its place.
This a temporary fix, lasting a few months.
Owner decides he doesn't want to deal with redoing the heads so flushes coolant with sealer in it and replace with new clean coolant, to sell the truck.

Now you have it and the sealer has failed after 4 weeks with no new sealer to replace it.


1988 was the last year of the old style 2.9l heads, which were prone to cracking, in '89 and up new beefed up style heads were used.
Pictures here: http://www.therangerstation.com/tech_library/2_9_Page.shtml

You can test for a cylinder leak(cracked head or head gasket leak) using a latex glove, search "glove test" here.

Or just fill up rad to the top on cold engine and start engine, leave rad cap off.
Coolant should not come out of rad cap opening, if it does then something is displacing coolant, air being pumped into head cooling passage from a cylinder displaces coolant.

Thermostat should be 192degF, NOT 180degF

I would test the temp gauge.
The sender for the temp gauge is a ONE wire sender, not TWO wire sensor.
There are two temp units on all fuel injected motors, the sender for the dash board gauge and the ECT sensor for the computer.
They are usually located near each other by t-stat housing.
Locate the ONE wire sender on intake
Turn on the key
Assuming cold engine, gauge needle should be low
Unplug the wire from sender, see if needle moves
Now Ground that 1 wire, needle should go to HOT all the way up.
Gauge can do the opposite, HOT when unplugged and Low when Grounded, that is OK, both types have been used.
If gauge works this way, full up and down movement, then gauge and wire are good, replace sender.

 

[adsm08]

What is an air pressure sensor cap?

There isn't even any sort of "air pressure sensor" on the 2.9. The closest thing is the MAP sensor, which actually tends to measure vacuum more than it does pressure, since the intake is under vacuum, not pressure.