Abnormal temp gauge reading?

[adventr]

Went with a couple other 80s to hit the trails today, and on the drive down (2 lane road, 40-50mph speed) I glanced at the gauges and noticed my factory coolant temp gauge was showing 3/4, when it only ever shows just below half.

Pulled over to inspect, and the engine didn't seem hot at all. I could hold my hand on any part of the radiator/hoses/heater lines/thermostat housing without it being too uncomfortable.
I kicked the a/c on to see if it would cycle, and it did.

I know from experience that the a/c kicks off with the factory gauge just barely above half, and this was well above that point, but the a/c still worked,

Also, my fan clutch (black hub) has been modded with 20k fluid, and timed to kick in at 95 degrees. It was NOT engaged when I pulled over to check it out.

Engine was running and sounding fine, coolant reservoir was at its normal level, and all signs point at the engine not being hot.


After inspection, we continued to the trails, where the temp gauge gradually fell back to normal, and remained there for 3hrs while we ran a low speed trail.

On the way out, it did it again. Temp gauge climbed back up near the red, and I pulled over to inspect, only to find the same things I mentioned above. I even popped the radiator cap, and no excess pressure.
Again, the temp gauge slowly returned to the center range, but stayed a bit higher than normal,

Once we hit the interstate, I figured I'd try to get it "hot". Left OD off, and stayed on it hard up the hill climbs. Temp gauge never moved a bit.



Outside temp was in the 40s today, so nice and cool out.




What do you guys think? Temp gauge sending unit?
Also, is the a/c shutoff sensor separate from the temp gauge sensor? If so, that might explain why the a/c would still cycle with the gauge showing near the red.

Anyone else experienced this?

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[adventr]

No one has had issues with temp sending unit?


I just ordered one of the koso gauge setups so I'll be able to compare the two. Hopefully I can repeat the results once that's installed.

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[western flyer]

My FJ 60 showed these same symptoms when it had a partially clogged radiator.

 

[adventr]

Hmmm, radiator is less than a year old, but I did just drain the coolant and refill with a heavier mix a couple weeks back.
Maybe air in the system?

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[greentruck]

Hmmm, yeah, I'd check for air just to be sure the bases are covered. But if it's been a year? BTW, assume no movement in the overflow bottle that you've noticed, i.e. not using coolant?

You said the fan was not engaged. But shouldn't it be if things are getting hot? I wonder if that little springy thing broke in your clutch, even though it's got fresh fluid.

Just guessing here, but doubt it's the gauge or sender. I'd keep at diagnosing until things get pinned down. If the factory gauge is showing motion, it's time to pay attention

 

[adventr]

Hmmm, yeah, I'd check for air just to be sure the bases are covered. But if it's been a year? BTW, assume no movement in the overflow bottle that you've noticed, i.e. not using coolant?

You said the fan was not engaged. But shouldn't it be if things are getting hot? I wonder if that little springy thing broke in your clutch, even though it's got fresh fluid.

Just guessing here, but doubt it's the gauge or sender. I'd keep at diagnosing until things get pinned down. If the factory gauge is showing motion, it's time to pay attention

I drained/refilled coolant about 2 weeks ago. The year ago was when the radiator was replaced.

The fan would be engaged if things were truly hot. What I'm saying is that things weren't really hot.
No movement of coolant reservoir either. Fluid in reservoir was cool to the touch as well.


I could hold my hand on the main heater line that comes out of the block and runs past the head. That's a pretty good indicator to me that the gauge was just wrong. That and the fact that the a/c would still cycle.

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[western flyer]

You said you just changed over to a "heavier" mix of coolant. This sounds like you might have been running a "summer" coolant mix, with a low concentration of anti-freeze. Any chance you were running close to straight water (very little anti-freeze) before? If so, corrosion can clog even a new radiator pretty fast. The anti-freeze provides a fair amount of corrosion protection for the cooling system internals (particularly in comparison to water by itself). If your radiator is clogged you can have hot and cool spots in your cooling system. When the rad in my 60 was clogged the gauge would do what you indicated for your gauge; thus, my earlier post.

 

[adventr]

Just finished installing my koso digital water temp gauge. Drilled and tapped the water neck on the block (as described in a different thread). Took it for a test drive, and.....



We have a problem. It's 41 degrees outside, and the cruiser was running over 200 degrees. Just slow driving around town gets it the hottest! On the highway ( running 70mph) it was 205-206. In town (driving 30-35mph), it got up to 216!

So what's going on here?

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[adventr]

Few more details that I think are important:


Fan clutch is VERY strong, and is timed to kick in, but with the air so cold outside, it is NOT kicking in when driving. Once I got back to my house and let it sit at idle for a bit while I looked under the hood, it did kick in, and upon me idling the engine up the temp promptly dropped to 190. The fan then faded back off and the temp begin to rise a couple degrees.
Sounds like a bad fan clutch, right? Wel... I don't think that's the issue. The fan pulls a ton of air through the radiator when it is engaged, and that air being so cold causes the fan to disengage.

So, my guess is clogged radiator like someone mentioned above? Maybe thermostat? Could it be water pump?


The whole cooling system felt warm, but the coolant in the reservoir was cold to the touch (i pulled the tube out and let it drip on my hand). I would think at 216 degrees, it would be pushing some out into the reservoir??

 

[adventr]

Also just went out and checked for common HG issues, to rule that out. It just passed the block sniffer test twice (I purchased the tool last year), and there are no bubbles in reservoir with engine at 3000rpm, and no signs of milky substance under oil cap or on the dipstick.


I do need to get this sorted out QUICKLY though, or I'll have to cancel my trip (leaving early Friday morning).

 

[Traction56]

I might have missed that you replaced it recently but, possibly a thermostat. Just had the same symptoms and a new thermostat fixed my problems.

 

[adventr]

I might have missed that you replaced it recently but, possibly a thermostat. Just had the same symptoms and a new thermostat fixed my problems.

I've never replaced the thermostat in it. I'll give that a shot tomorrow!

Also, been searching on here and found that there is a right and wrong way to orient the thermostat when installing it. The little ball goes at 12 o'clock, I read.
Well, I had the thermostat housing apart several months back, and it's quite possible that I didn't put the ball at the 12 o'clock position when I re-installed it.

 

[jeffro109]

I think low speed, higher temps is normal, but not that high! I see the highest temps on my scangauge just going through the heighborhood hills at 20mph compared to anything else.

I'm sure you know this, but will mention it anyway. You can turn the heat to full blast and rear heat too if you still have it, and it will help cool things down in the engine as a stop-gap in the mean time should you have to drive across town or something.

 

[REKCUT]

I dont think I read anywhere that you have looked at the water pump. It sounds like you are not getting good circulation out of the cooling system. I also have the KOSO gauge and its nice to know real time temps.

 

[CJF]

I dont think I read anywhere that you have looked at the water pump. It sounds like you are not getting good circulation out of the cooling system.

Water pumps don't fail that way.

 

[adventr]

Well, I've spent ALL day trying to figure out the problem and get it fixed before my trip tomorrow, but alas... looks like that's not going to happen.

I flushed/backflushed, changed thermostat, bled, cursed...ect.


Finally figured out the problem. Radiator is toast. The center of the radiator is ice cold, while the rest of it is really hot. That explains why my fan wasn't kicking in, because it was pulling cold air through the center.
Tried flushing it out, to no avail. Previous owner had replaced the original radiator with some aftermarket aluminum/plastic job, that I was never fond of.


So.... $$$$ later, I have a brand new OEM radiator, water pump & hoses coming from Toyota. Hopefully it's here next week sometime!

 

[adventr]

Western Flyer called it early on.

 

[retrofive]

Western Flyer called it early on.

Well at least you know now . Same thing happened here, but little different symptoms. Same as you half my radiator was cold..... new installed and happy again.

 

[western flyer]

Western Flyer called it early on.

Cool! No pun intended. Glad you figured it out.

 

[adventr]

Just to update thread for future reference.


Installed new brass/copper radiator along with new hoses and thermostat this evening. Broke my fan shroud trying to reinstall... So I had to leave it off. lol

Despite that, it went pretty well, and now the Koso digital temp gauge never goes above 185.
Ordering a new shroud on Monday.

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