Diagnosing high temperature issue (3 Viewers)

[FJ Noob]

I've been reading through the related threads and trying to narrow down my diagnosis before I just wholesale start replacing parts. To help me think it through better, I need confirmation of the coolant flow direction. In the FSM it looks like the coolant should flow from the t-stat housing through the big fat upper radiator hose INTO the radiator, not from the radiator to the t-stat. Is this correct?

 

[Hojack]

When your coolant gets hot the t-stat opens at is specific set temperature allowing hot coolant into radiator to start providing cooling. Thermostat to radiator.

 

[Seth S]

Yes hot coolant top hose cold coolant bottom hose

 

[FJACS]

If you’re basing your high temperature concerns on data from the stock in-dash temperature gauge... start by determining if you actually have an issue. The gauges are notoriously incorrect.

 

[Prairie Swamp]

Yes hot coolant top hose cold coolant bottom hose

This - on any car ever (I think). As the coolant cools going thru the radiator it's going to want to naturally sink to the bottom. So the design utilizes the natural flow.

 

[OSS]

95% of the "Engine is running hot" threads were started because the temp gauge in the cab was reading high. That gauge is not reliable. Often the engine wasn't running too hot, just the gauge was inaccurate.

Get yourself a infrared temperature sensing gun (Harbor Freight) and use it to verify the engine operating temperature before doing anything else.

 

[FJACS]

Take a reading on the thermostat housing when the engine is at operating temp and running 180-200F would be ok.

 

[FJ Noob]

95% of the "Engine is running hot" threads were started because the temp gauge....

Yep...saw all that. Will double check with an IR sensor, but it is within a normal-ish range on the highway with recent cooler air temps. Begins rising immediately when I exit and slow down. Fan clutch passes initial inspection.

After running it last night to test after changing the t-stat, the upper hose was hot and VERY full. The radiator was hot up top and SIGNIFICANTLY cooler half way down. The lower hose was barely warm and didn’t seem to have much fluid in it when I squeezed. I’m thinking a blockage in the radiator?

 

[John McVicker]

Like you said, you won’t really know until you get that IR gun. Everything else is just a guess.

Get the gun and see what, where and if you have an issue. Even the $29 Harbor Freight will work for this.

 

[OSS]

Maybe the radiator is shot.
That would explain it’s inefficiency

 

[SteveH]

The lower hose was barely warm and didn’t seem to have much fluid in it when I squeezed. I’m thinking a blockage in the radiator?

I have seen the bottom radiator hose stay fairly cool on warm days. It only got truly hot on very hot days, or after a long drive. To some extent, a cool lower radiator hose means the radiator is doing its job - rejecting heat to the atmosphere. So, IMO, the temp of the lower radiator hose is not a full indication of either a functioning or non-functioning cooling system.

You might also shoot your IR temp gun at the head on a warm day at full operating temperature. With a 190F t-stat, my FJ62 reads about 200-203 along the head, which is fine with me.

 

[FJ Noob]

Got an IR gun, but won't be able to get off work in time to really dive into this until probably Friday. For reference though - in a perfect world where the truck's systems are working properly and the temp gauge is accurate, about where should the needle be at normal operating temp....bottom quarter, half way, somewhere in between or above? It's been a long time since I've driven an '87 Toyota.

 

[FJACS]

Mine is a tick past the middle.

 

[Seth S]

Easy test to do with nothing other than your face. Start the truck and get it to normal operating temp. Open the hood and stand next to the drivers side fender so the air from the fan blows on you. If things are normal you will feel the air switch from warm/cool to hot and back fairly often. This indicates your coolant is flowing, the t stat is opening and closing, and the coolant is cooling.

 

[BlackCat]

In cool weather mine runs right in the middle, or slightly below. When it’s 115 out and the A/C is on, it’ll run over half way. IR temp gun shows it at approx 210 at various places on the motor on those days. I think the hottest I’ve IR’d mine was 216 after driving home from work and letting it idle in the driveway with the A/C on for 10 minutes when it was 115 out.

 

[FJ Noob]

Got off work a bit early today so I decided to have a go at this again. I ran the engine at the house for about 15 min and then drove around for about 20 min to get it fully up to temp and the gauge started going high (no surprise). Using the IR gun, I got a consistent 197-200* from front to back of the engine block along the side with the spark plugs...good news. I used the $26 HF gun. It has settings for 'emissivity'. I set it for cast iron for the engine block. What is the thermostat housing made out of? If I set it for cast iron, I get around 205-210* at the housing. If set to aluminum, it says 245*. I didn't really pay that much attention to its weight when I changed the t-stat.

I'm erring on the side of the actual engine temp is fine, but the high t-stat housing reading and question of proper setting still leaves me with that 10% doubt.

The other 90% is saying this is an inaccurate gauge issue. For those of who've dealt with your gauges...

Is emory paper the contacts, check ground, check wire is intact pretty much the protocol?

 

[FJ Noob]

[QUOTE="SteveH, post: 12745086, member: 5367"
I have seen the bottom radiator hose stay fairly cool on warm days.....
[/QUOTE]

Totally makes sense. I've never really had a reason to check out a radiator like that and just thought the extreme difference from top to bottom seemed odd.

 

[60 toy ota]

the fSM outlines values for resistance with respect to temperature at the sending unit, and I believe it also gives values for resistance between the gauge and ground and where the needle should be based off of that resistance. When there is no resistance between the gauge and ground, ie if you just touch the wire to ground and bypass the sending unit, it should Peg your temperature gauge

 

[4runner2FJ60]

I wonder about the sending unit burping we PM'd about a while back, but i think that issue shows drastic differences in temperature and gauge goes all over the place. Somewhere deep on my list of things to get to is fixing my temp gauge that only reads slightly past low after running a while. But i have to be running to work on that!

 

[FJ Noob]

I wonder about the sending unit burping we PM'd about a while back, but i think that issue shows drastic differences in temperature and gauge goes all over the place. Somewhere deep on my list of things to get to is fixing my temp gauge that only reads slightly past low after running a while. But i have to be running to work on that!

I was planning on replacing the TSU anyway and making sure there's no bubble, but I'm also waiting on a part from vintageteqparts to be delivered with it....amazon prime has made me impatient.