engine and drivetrain Engine Temp Questions - Faulty Gauge related

[rho]

What temps should I expect from these parts of the engine while using a IR temp gun.

Radiator Cap

Coolant temp Sender Housing

T-Stat

T-Stat Top Hose

T-Stat Bottom Hose

Reason being, My temp gauge jumps about 1/2 inch when I turn my headlights on (I know, bad ground or connection) and in addition, the needle creeps up close to the RED on the freeway at speed.

While the needle was reading close to the RED the Radiator cap showed 200F and the Sending unit housing (connected to the head) was 211F. Is the gauge correct or is my electrical system inaccurate?

I'll have to confirm those numbers again (I wrote them down but I'm at work right now)

Thanks

[Mike Self]

then you'll know if you're overheating or not.

Keep in mind that an '02 runs a 1 A (14.7 psi) radiator cap, which increases the boiling point of your coolant considerably so the readings you obtained aren't necessarily high. With the temp gauge sender in the upper radiator hose outlet at the engine, it's picking up the coolant temp at its hottest point before it flows into the radiator, so presuming the gauge is reasonably accurate, you can assume all is well if there's no overheating and the coolant level is normal.

cheers

mike

[ingraham]

See Ben Thongsai's excellent cooling system description at http://www.bimmers.com/02/. Click Engine under FAQS & Specs, then click Cooling. Excerpt:

"Starting at the water pump, the coolant is pumped into the engine block and up through the cylinder head. Most of the coolant exits the engine at the top of the cylinder head, at the hose flange next to the intake manifold. From here, the coolant flows either to the thermostat or to the radiator. If the engine is below the thermostat opening temperature, the coolant flows to the thermostat to warm it up, and from the thermostat it flows back to the water pump and into the engine. If the engine is hot, the thermostat shuts off the flow from the top of the head back into the engine, instead forcing the coolant to flow to and through the radiator. The coolant is cooled as it flows through the radiator and emerges from the bottom hose of the radiator to the bottom half of the thermostat. This cooled coolant then flows to the water pump and into the engine."

So the temps go from highest to lowest in roughly this order:

- Coolant temp Sender Housing

- Radiator Cap

- T-Stat Top Hose

- T-Stat

- T-Stat Bottom Hose

With 211 F at the temp sender housing, your temp gauge should read a bit below the start of the red zone, which is 239 F (115 C). So aside from the electrically induced jumps, your gauge is fairly accurate. The needle should normally sit near mid-scale. If it usually rises at freeway speed, your cooling capacity is below normal, probably due to an aged, inefficient radiator.

[rho]

, so presuming the gauge is reasonably accurate, you can assume all is well if there's no overheating and the coolant level is normal.

cheers

mike

Were you referring to the accuracy of the Temp gun? I assume so since I"m almost certain the car's temp gauge is whacky.

[rho]

Ok here are the readings I had when I got home... Temp needle 1 to 2 needle thicknesses from the red.

Radiator top hose to sending unit housing = 180

Radiator Cap = 111

Bottom of Radiator Left = 141

Bottom of Radiator Right = 150

Head = 200

Intake manifold = 153

Header = 460

T-Stat = 156

Hose up from T-stat = 200

Hose below T-stat = 161

Hose from Intake manifold to firewall = 205

Temp Sender housing = 225

Hose to carb from sender housing = 201

Could it be a bad radiator knowing that the temps taken were 111, 141 and 150?