Overheating issues RTH needed (1 Viewer)

[wierdbeard]

Ok, I’ve had my 97 40th triple locked sweetheart since jan of 06, she’s been my daily, I replaced the radiator once before I think 10 years ago. Lately she’s sat because I was going to school from home so there was no need to drive. I started back on campus recently and the radiator went. I replaced it with another Koyo. I’m on a super tight budget and was unable to do the whole package of items I would have liked, but now I have a problem.

I bled all the air I believe, ran Asian red coolant, unable to drain the block this time due to the location of where I was working on the rig, I have a new thermostat but not the gaskets yet, it ran for 20 minutes, reached 180 then opened hit 195 stayed steady. In the 30 minute drive to campus it jumped to 220. What the actual?????

Help, I’m at a loss. There wasn’t any play in the water pump, the fan clutch is a modded blue hub from land tank I put in when I did the radiator previously, I don’t have any leaks, and there wasn’t any oil in the coolant nor couldn’t in the oil.

I am seriously stressed out about this.

 

[Fj80oregon]

Are you sure your thermostat opened all the way also if you didn’t get all the air out that can cause issues. If you jack the truck up and run it it sometimes helps with the air getting out. I prefer a coolant filler funnel they work great bleeding the air out and don’t make a mess.

 

[LandTank87]

Are you sure your thermostat opened all the way also if you didn’t get all the air out that can cause issues. If you jack the truck up and run it it sometimes helps with the air getting out. I prefer a coolant filler funnel they work great bleeding the air out and don’t make a mess.

View attachment 3139834

Im going to add that even parking the truck on a sloped driveway/street with the engine on the high side will help be sure you have all of the air out.

Could be a few things, first thought is your t-stat is acting up or not opening consistently (may be installed upside down or out of the 15deg range either side of the prescribed position?). If that's not it, my second thought would be to check the internal blades and bearing condition of the water pump. Either way, sounds like you are going to be draining the coolant again. I would suggest draining the block this time also.

This is from the FSM...

 

[wierdbeard]

So I do not have gaskets to install a new t-stat. It’s the same one that’s been in there since I previously put in the radiator years ago. I’m currently 30 minutes away from home, so removing the water pump in the university parking lot isn’t really an option either. It’s been sitting for about 2 1/2 hours so I’m going to see how much it’s cooled off. If there’s air at the top of the radiator I’ll add fluid. Should I try going to get it flushed, there’s a lube joint about 5 minutes from here. I hesitant to drive all the way back across town.

 

[LandTank87]

If its cool enough to open the radiator cap, maybe check the fluid. If it looks off color or smells burned, flush might be a good step to getting you home. Also, Koyo outsourced to China/Indonesia some years back (only the racing aluminum are designed/manufactured in Japan now), and while some have had good success with those rad's, others have not and they failed in 30k miles. Ask to see the fluid that they flush and if you see rust, its likely coming from the radiator. Overall, a flush isn't going to hurt, and could give you some more info.

 

[Malleus]

So, just having gone through all this, I'll say:

1. The thermostat STARTS to open at 185°F, ±15°F. It FULLY opens (at least my tested thermostats did) at 210°.

2. I've emptied and filled a number of 80 radiators, of various makes, a further number of times, and never gotten an air bubble in the system, anywhere, whether I pulled the block drain plug or not. I know some engines can get these, but I don't see how the 1FZ-FE can, since the outlet is above the engine. (FWIW, I've started refilling the coolant by using a transmission ATF-type funnel in the outlet hose) I personally wouldn't worry about this being a problem.

3. I have (2) 1995 80s. One (w/ 2325k on it) runs at 174°F always, no matter what I do with it, with all factory parts in the cooling system (less hoses). The other (w/ 310k on it) (...and with a recently rebuilt head) runs reliably at 184°F, unless it's climbing (I mean a mountain) and then it'll peak at 235°F. Both have OEM parts, except for a recently rodded and resoldered brass and copper tube CSF (which I love, BTW), in the hotter model).

4. When I replaced the entire cooling system in the second 80, one part at a time, during the head rework, I tested the OEM thermostat. It failed, even though it was
only 3 years old. By failed, I mean it opened at around 185°F, but failed to fully open, no matter how long it sat in boiling water.

So, a couple of questions:

1. How do you know what the temp is? I use Torque Pro and a bluetooth dongle.
2. What was the temp prior to the recent radiator replacement?

I will say that the second 80 has a transmission with suspect clutches, and I think the heat from there is adding to the radiator temperature, but I won't know for sure, until after I replace the clutches.

 

[wierdbeard]

Ah, to answer your questions, I run a ScanGuage2 mounted in the cab to monitor the system.

Prior to replacing the radiator, my normal operating temps were 190-198 throughout the year. Reaching the higher end sometimes 202 if outside temps were 110 plus and I was under a load in the hills. I don’t have the part number handy but the koyo rad is the same one I bought a decade ago that was supposed to be the Japanese sourced model.

I’m doing the flush now, it was low, they did find some sediment in the old fluid in the block.

 

[Malleus]

Based on your prior temps, I suspect the thermostat isn't opening fully. The amount of water flowing through between half open and fully open is significant, given the small area of the thermostat housing.

In a pinch, you can reuse the thermostat gasket, if it isn't broken.

 

[jonheld]

2. I've emptied and filled a number of 80 radiators, of various makes, a further number of times, and never gotten an air bubble in the system, anywhere, whether I pulled the block drain plug or not. I know some engines can get these, but I don't see how the 1FZ-FE can, since the outlet is above the engine.

Exactly. The coolant system self bleeds. That's one of the purposes of the overflow bottle. Any air trapped in the system will find its way to the top of the radiator. As the system cools, fluid from the overflow is pulled back into the system to maintain the coolant level.
Fill radiator to the top of the filler neck, fill overflow bottle to the high line. After 1 or 2 drive cycles recheck levels. Done.

 

[Devils Paw 80]

Ah, to answer your questions, I run a ScanGuage2 mounted in the cab to monitor the system...

Any chance it's giving you a faulty reading? What does the idiot gauge say when coolant is supposedly over heating.

 

[Marco Lau]

Any chance it's giving you a faulty reading? What does the idiot gauge say when coolant is supposedly over heating.

My digital temp gauges indicates 235 F when the stock coolant temp gauge show right about 3/4 from the red.

 

[Malleus]

FWIW, that coolant gauge is the only one on the dash that's worthless. It's only right twice, just like a broken watch.