So I'm stumped.... (1 Viewer)

[Jesper]

My '83 FJ60 has been running hotter than I think it should...still in the operating range and often around halfway, but when driving highway speeds for any period of time the temp needle starts to creep up into the top third of the white zone. Anywhere in the white zone may technically be "normal" but I'm expecting to see the needle at halfway or slightly below.
The PO replaced the smog pump with an old alternator, consequently the belt used for the water pump is thinner and has shorter, less aggressive "teeth" than the stock belt. I noticed while replacing the fan clutch awhile back that when I put a wrench on the fan to loosen the bolts I could spin the water pump pulley under the belt, even when tensioned.

I decided this weekend was time for my cooling system overhaul and put this nagging issue to bed.

I pulled the radiator and had it pressure tested and cleaned. The guy said there wasn't any significant sediment or junk inside - not enough to make it run hot. I replaced the water pump, just because. I installed one of Jim C's idler pulleys as well as a proper belt (the pulley doesn't slip while I tighten the fan now). I installed a water temp gauge (sender in the upper radiator hose) in addition to having the stock gauge. I replaced the thermostat and all hoses a few months ago as well as the fan clutch. Put in new coolant and got some good burps - good heat at the front and rear heaters.

Imagine my surprise when I find the stock temp gauge climbing right back up to the top 1/3rd of the temp gauge - even while idling, which it didn't do before. All the while, my new water temp gauge is telling me that it's at 190-195 steady.

I can't imagine that the truck would run hotter now than it did before, but I'm also leery knowing that the new temp sender in the upper radiator hose can get different temps than the sender at the back of the head. Even with the difference in locations I can't imagine the difference in actual temps would be that large. I guess the stock sender system or gauge itself could be faulty due to age...don't know which indicator to put my trust in.

Also - probably because I'm paranoid now - but I swear the valves or pushrods are louder than they were before I did the weekend job. I didn't touch anything other than those items I mentioned so I find myself overthinking this....could the resonance of the block or head be different due to coolant not circulating properly or am I crazy..what could cause this, besides my imagination?

Thoughts appreciated.

 

[Cruiser Jimmy]

According to your signature you're in a state that is cool...compared to say south Texas. My thought is your sending unit is putting you at discomfort. You've replaced everything else that's required for a cooling system to operator properly. Circulation and pressure are the two main factors that you have addressed.

 

[White Stripe]

You can test your factory sender, but I imagine it's probably bad and I would just replace it. If you have a temp gun you could check the temp at the sender. Also if the timing is too advanced it can raise motor Temps. Could be based timing needs adjusted, or perhaps something with the mechanical or vacuum advance is screwed up, which happens with some Toyota distributors when they get old. First I would verify how hot the motor really is getting though. Having a aftermarket sender in the upper hose sucks because it's before the thermostat. You need a temp reading of the cooling system after the thermostat. Coolant flows through the head, through the thermostat if it's open, then through the upper hose.

 

[John McVicker]

I agree with the IR gun. Test the temps with that and put your fears to bed...or at least know one way or the other if you have a problem.

John

 

[Landpimp]

Have you done the tstat? Maybe the o ring is missing.

 

[Cruiserdrew]

Probably that voltage regulator for the dash in the fuel gauge is bad. Makes the temp gauge read high.

Do a search on that, lots of info. Bottom line, replace the fuel gauge, as crazy as that sounds.

 

[Output Shaft]

You have a brand new temp sensor installed in the water inlet hose to the radiator. You also have a brand new gauge. Go with that. 190-195° is perfect.

When the engine is pushing the car, the thermostat sure as hell is open enough to let at least some of the waste heated coolant flow through that hose. It doesn't matter if the thermostat is fully open or just cracked open a little. The temperature flowing through the thermostat to the radiator is the hottest coolant in the engine.

What you're now experiencing with new "elevated" temperatures at idle after you drained the coolant is something I have been suspecting for many many years.

There is an air bubble trapped underneath the stock sender giving erroneous readings. It's a faulty design and was fixed with the 3F-E engine.

The stock sender at the back of the 2F head is elevated above the head in an adapter bushing. It isn't submerged down into the water jacket of the head.

This creates a pocket that traps air. Air that prevents the sensor from being fully submerged. The heat from combustion heats the metal of the engine which then eventually heats the coolant flowing on the other side of it. The coolant is the coolest part of the engine. The metal is the hottest.

My suspicion as to what is happening to all of us with 2Fs who change our coolant only to see elevated temps on the stock gauge for many days afterwards is both trapped air in the head, but more specifically, a trapped air bubble underneath the stock sender.

Without the lower temperature of coolant to cool it down (since it isn't fully submerged because of the air bubble) the sensor gets heated up by the cast iron of the head which is retaining the bushing.

And since we know that the metal of head is hotter than the coolant flowing through it...... This would explain why the damn temp sender in the 2F is reading higher temps till that damn air bubble slowly diminishes after several heat cold cycles.

I could easily be wrong about this, but that's my theory for today at least.

The engine isn't running hot. Just the temp sender.

 

[cwwfj60]

smart thinking OS, sounds like a reasonable suspicion

 

[Trapper50cal]

that's why I always fill the radiator with the front of the truck elevated and continue to fill
while the engine is idling...to burp it and get those air bubbles. (start with rad cap off, don't
let it build up heat/pressure then try to remove, obviously)

It has been my experience that one can get the system too full this way, but it just purges
into the overflow until it's the right level.

 

[Jesper]

Thanks much for all the input.

Follow up:
I got an IR temp gun and did some road testing.
I noticed the stock gauge is slowly working its way back to the "normal" part of the scale - which jives with the air bubble theory that Output spoke of, I think you hit it right on the money there.
At highway speeds my aftermarket gauge shows 190-195 steady. I would pull over occasionally and scan 4 spots on the engine to compare;
1) the aftermarket sender housing in the upper rad hose
2) the thermostat housing
3) the side of the cylinder head on the passenger side - right between the #3 and #4 spark plug holes
4) the top of the cylinder head - driver's side, around the stock temp sender towards the rear of the head.

The IR scanner indicates that when the aftermarket temp gauge is reading 190-195, the temp is roughly the same in all locations except the top of the cylinder head on the drivers side. In that area the temperatures show 70-90 degrees hotter. 270-290'ish at normal highway speeds in that localized area I expect that to some extent with the exhaust manifold being right there, and although I'm happy to find that it seems my engine and cooling system are working properly I'm wondering how hot the cylinder head can get back there before it risks cracking, warping or other damage.

Also, CruiserJimmy - I'm currently in New Mexico, plenty warm and about 4100' above sea lever.
LandPimp - did the thermostat and O-ring a few months back but stuff like this makes me rethink and second guess everything.

A few pics of the temp and vacuum gauges installed, warming up.

 

[John McVicker]

Hmmm, I don't know about your high temps at your d/s rear of the head. As a point of reference consider this:

About 2 weeks ago I installed an aftermarket electrical temperature gauge. I used the stock OEM temp sending unit. Here's what I found when checking with my IR gun & after warming up the engine for about 15 mins @ 2k rpm.
A) 200* at the aftermarket gauge
B) 198*-199* at the sending unit using the IR gun

Now I did this in the driveway, @ about 2k rpm, so it's a different test than what you did, but still, your 270*-290* is a LOT different that what I experienced.

You might be ok, but let's see what others say. Great looking interior btw.

John

 

[3_puppies]

when you drained the coolant, did you remove the plug on the driver side of the block? could be some gunk in there not letting coolant to circulate properly.
the rear driver side of the head will be the hottest, furthest away from rad. 70-90 degrees hotter seems abnormal tho.

 

[Jesper]

Great info, John. I'll definitely be keeping your results in mind as I troubleshoot this.

3Puppies - I didn't drain the block, just the radiator when I pulled it out. Replaced about 3.5 gals of coolant total. Since the guy told me he didn't find much within the radiator I assumed the block should be similarly free of sediment and gunk as well. Hmmmm.

 

[gregnash]

Keep an eye on your temps. If the aftermarket gauge is reading in the proper range then hopefully things are where they really should be. If you read back some pages on my build you will see that I started having a similar problem in November last year. For me it resulted in a blown headgasket and dying water pump as I found exhaust gases in my coolant.

Not to be the alarmist, but as everyone else has said the stock gauge is really bad. Keep a close eye on her for sure.

 

[Jesper]

Thanks, Greg. Trust me, you're not the alarmist. This truck and I got to know each other on the side of a Nevada highway about 2 hours after I bought it with a blown head gasket - so I'm paranoid to the point of conspiracy theories when it comes to overheating.

I just jacked up the front end, burped it again and "bled" the stock temp sender, backing it out of the head until coolant flowed out thinking it would disperse any residual air trapped underneath. I've been comparing temps again and they seem to have normalized. The driver's side rear is still warmer by about 20-30 degrees which I would think is normal with the exhaust and everything there. Going to do some more road testing.

Also, I was reading how a buggered up exhaust / clogged catalytic converter can create back pressure and localized hot spots in the cylinder head. I've had exhaust on my to-do list...might have just found the excuse I need.

 

[Skniper]

You can test your factory sender, but I imagine it's probably bad and I would just replace it. If you have a temp gun you could check the temp at the sender. Also if the timing is too advanced it can raise motor Temps. Could be based timing needs adjusted, or perhaps something with the mechanical or vacuum advance is screwed up, which happens with some Toyota distributors when they get old. First I would verify how hot the motor really is getting though. Having a aftermarket sender in the upper hose sucks because it's before the thermostat. You need a temp reading of the cooling system after the thermostat. Coolant flows through the head, through the thermostat if it's open, then through the upper hose.

@White Stripe Not sure what you are saying about the aftermarket temp sender in the upper rad hose. If the sender is in the upper hose then it is after the thermostat. It is reading the coolant coming right out of the motor which is the closest indicator of engine temperature, right? Heated water flows from the engine through the t-stat, through the upper hose, across the aftermarket sender, then back to the upper radiator, right? Granted, when the t-stat is closed the sender in the upper hose is just soaking in "non-engine" water, so to speak, and not giving a true reading of engine water temp...until the t-stat opens and the cycle repeats. If this is the case, I can see where a sender in the upper hose does not give a constant temp reading and is subject to temp spikes depending on t-stat function.
It may not be perfect but seems like a good check n balance against the stock temp gauge.

 

[White Stripe]

@White Stripe Not sure what you are saying about the aftermarket temp sender in the upper rad hose. If the sender is in the upper hose then it is after the thermostat. It is reading the coolant coming right out of the motor which is the closest indicator of engine temperature, right? Heated water flows from the engine through the t-stat, through the upper hose, across the aftermarket sender, then back to the upper radiator, right? Granted, when the t-stat is closed the sender in the upper hose is just soaking in "non-engine" water, so to speak, and not giving a true reading of engine water temp...until the t-stat opens and the cycle repeats. If this is the case, I can see where a sender in the upper hose does not give a constant temp reading and is subject to temp spikes depending on t-stat function.
It may not be perfect but seems like a good check n balance against the stock temp gauge.

I would rather have it in the tstat housing or something in case the tstat is sticking. I think u could t in a sender their without much trouble. Maybe it's not as big a deal as I made it out to be in my previous comment.

 

[Skniper]

I would rather have it in the tstat housing or something in case the tstat is sticking. I think u could t in a sender their without much trouble. Maybe it's not as big a deal as I made it out to be in my previous comment.

Gotcha, know what you mean. I think the 60's t-stat has some open real estate on it. I know the 62's housing is already VERY crowded.
I have a mechanical temp gauge still in the box with a rad hose inline sender still waiting to be installed. This thread is really renewing my interest to get that thing in there and see what's happening inside mine. At least my IR thermometer reads pretty consistent, but the stock gauge started reading sorta high a few years ago after reading very normal.