Temp Sender Reading High (1 Viewer)

[Bama4door]

A little background first. I have recently flushed and changed coolant in my 62 and all has been well for the past couple months. Recently I have noticed the temp gauge reading high. Usually it was when I was stuck in traffic or going slow it would creep up to just past half way and once I would get to driving it would go down.

I checked under the hood and noticed one of the idler pulleys wasn't spinning, so I replaced the bearing in it and got that taken care of. Now the temp sender is reading hotter faster. It's not leaking coolant anywhere and the fan clutch is spinning like it should. However, I just ran it for a while and got it hot and then shut it off and the fan would spin freely (from what I read the fan should not move once the engine is hot after shutoff). Does this indicate needing to add fluid to the fan clutch?

I got out my infrared temp gun and held it to the temp sender unit that's just above the WP (see pic below) and it reads anywhere from 205-226 at the highest when sitting there idling. 226* seems a little high to me, but the inside temp gauge is almost at the top in red (which from what I gather should indicate 265*). Is the temp sender unit the best place to hit with my infrared gun to measure accurate temp??



Any help on this would be appreciated. Could the sender unit be bad?

 

[Output Shaft]

Point the ir temp gun at the outside top driver's side of the radiator, directly across from the inlet hose. As pictured below. The IR temp gun is influenced by reflective surfaces. The ideal surface is flat black in color and flat in shape.

I have a FJ62 gauge installed in my 60. Same gauge as yours. It uses the exact same sender too. I just calibrated it against a new sender and this is what my needle position correlates to.


IR temp gun position:

Reference

The needle will always rise after slowing down at idle after driving. Thats normal. The coolant is soaking up the latent old heat and circulating more slowly so it has more time to heat up. The coolant may be getting hotter, but the engine is actually getting cooler. There is a big time lag.

You don't need to worry about what the temp gauge is doing when coming to a halt at a traffic light after diving hard (unless the needle pegs into the red). The moment you take your foot off the gas, the engine is cooling down. What you're looking at while waiting for the light to turn green is old news.

A free spinning fan is normal for an engine at normal operating temp. The radiator has to be really hot in order for it to lock up the fan clutch.

But if your fan clutch is more than maybe 10 years old, I'd replace it.

 

[Bama4door]

@Output Shaft awesome, I appreciate your response! I put the IR gun on the radiator a few times as well and it was significantly cooler (180-190*). I'm going to try burping the coolant one more time and put the truck up on some ramps and use a coolant burping funnel and see if that helps out at all. There may be a bubble near the sender that's making it read hot.

 

[Output Shaft]

There could be air in the system, but the temperature sender orientation in the FJ62 thermostat housing doesn't trap air. The sender is horizontal and at the bottom of the housing. No trapped air there.

Its possible that the radiator isn't as efficient as it used to be. But probably the first thing I would do when trying to find potential hot running engine issues is just replace the fan clutch to rule that out. It's always a bit of a mystery as to whether it's working correctly or not and it's pretty cheap (at Rock auto) and not difficult to replace.

 

[Bama4door]

@Output Shaft I just got done burping the system and there must have been air in the system because now the gauge is on the 1/4 mark where it usually runs. Thanks again for the help!

 

[Shacklewhacker]

Not to be anecdotal, but I will share some temp info about my 87 FJ60 with 150K miles on it.

On normal days (65-85 degrees) at operating temp, it will not see above 205 degrees at idle (measure infrared, at return on top of radiator, or at thermostat housing). In fact, the fan clutch kicks in with the famous voracious roar at about 200 degrees. Fan clutch, fan, and coolant were replaced about 5K miles ago - I strongly recommend paying the extra $50 for the OEM clutch vs aftermarket.

Now, here in California in the summers, I see a few weeks at a time that are 95-102 degrees regularly. My AC works quite well still (converted to R134 in 2002). After driving, with the AC on, if I let it sit and idle (w/AC still on) it never measure above 210-215 in either of the same measuring spots. Now, remember, the AC causes a high idle (about 1400 rpm) to compensate for the compressor load. Again, the fan clutch is fully engaged with that wonderful roar. In fact, with the hood closed, and the AC high idle, and the fan fully engaged, the draw through the grill is strong enough to suck and hold a beach towel against the grill.

The only time I see temps above the 225/230 range is after running, and the car is turned off for about 4-5 minutes. The heat soak (as Output Shaft describes above) and lack of circulation of coolant allows the temp to spike up a bit. But it comes down over time (within 30 minutes or so), or very quickly after restarting the car.


I think trying to bleed the system one more time as you said is worth a shot, but you honestly may want to look into a new fan clutch, and possibly a sticky or slow responding thermostat.

You have to remember, these things were built for service all over the world - the cooling systems on these beasts were engineered for climates ranging from 40 below zero, to 125 degrees. It's why they are still all over the middle east (and yes - not only diesel versions - gassers like US market).

I honestly do not think you should be measuring running temps above 225/230 range in most any circumstances.
Just my $0.02...