Hello,

I recently bought a 1991 Toyota Pickup base 2WD with the 22RE with 150k miles. About a month ago, I decided to put in a new timing chain, water pump and oil pump since I didn't have any history of the truck and figured it'd be good to do. I installed the LC Engineering kit with the metal guides, as well as a new thermostat. Everything ran great for a few weeks/250 miles, but about two weeks ago it started to overheat while driving. I immediately pulled over, popped the hood, stood around for a few min, then got in and started driving, and it seemed to go back to normal so I didn't think too much of it.

However, after that the truck kept overheating, even though the coolant levels looked fine and the heater blew hot. The upper radiator hose and thermostat cover never got hot, so I figured it was the $6 Stant thermostat, so I bought a single stage OEM Toyota thermostat and put that in instead, and had the same problem. The OEM thermostat felt a little sticky when opening it with my fingers, so I returned it and ordered the dual stage OEM thermostat.

In the mean time, I gutted the Stant thermostat and put that in the truck to test if the water pump was still circulating coolant, and it was running fine. The upper radiator hose was getting hot, and the truck (obviously) wasn't getting up to temp (gauge was barely off the low line), so I figured it was the thermostats I had bought being faulty. I also completely flushed the cooling system with distilled water before installing the dual stage thermostat, but again after installing it the truck is overheating.

Is there anything else I can check? I'm going to pressure test the cooling system, but I am very confused as to what else could be the issue. I don't see any oil in the coolant, coolant in the oil, white smoke coming out the tail pipe or coolant levels dropping, so I'm hoping it's not the head gasket. Just wondering if there's anything else I could be missing (other than a blown HG). Could it be an air bubble stuck somewhere near the thermostat?

Thanks for any help!

 

have you verified that it actually is overheating with an infrared meter. in other words, it could just be the dash gauge is reading incorrectly.

 

I have not yet, where should I point the thermometer to verify the coolant temp?

The temp sender is brand new as well.

 

when my truck is up to temp, pointing the thermometer right at the thermostat housing it reads darn close to the 195*. That is the thermostat i am currently running.

 

My thermostat housing and upper radiator hose still stay cool to the touch (radiator is ice cold), even when the temp gauge start creeping up past halfway.

I'm starting to notice a bit of white smoke and a misfire if I rev the truck enough. I'm thinking it might be the head gasket. I will try a compression tester to verify.

 

Look for milky colored condensation under your oil cap, this is a quick check to see if coolant is getting through head gasket and into oil port or cylinder. I assume you kept the head on while replacing timing chain? It's possible the head gasket may have been damaged.

 

First thing I'd do is do a chemical block test. You can borrow one from one of the chain stores tool loaner programs. I'm assuming they'll have you buy the fluid.
It's easy to run and will get a big question mark answered quickly.

 

I don't see any condensation, but the coolant is new and has about 5 miles on it, so I'm assuming it wouldn't have built up by then?

I did leave the head on while replacing the timing chain - I didn't think that the head gasket had any coolant passages near the timing chain cover, but I guess that would make sense.

The O'Reilly and Autozones near me don't have that tool... I will have to keep looking.

 

Please clarify which^^^ is which at this point in time.

Absolutely no coolant loss? Coolant reservoir not over flowing?

 

With the thermostat removed, the upper radiator hose gets hot. I ran the engine without the thermostat to test if my water pump was still circulating water or if anything was clogged. With the thermostat in, the upper radiator hose and radiator do not get hot at all.

I didn't notice any coolant loss when it first start overheating, but since then I haven't been able to drive the truck to even tell if the coolant level is decreasing or not. I chalked up any small decrease in level as air burping out of the system since I had just refilled the coolant. The last time I did run the truck, I did see some white vapor coming out of the tail pipe, even though the truck hadn't been sitting for that long (I had started it earlier in the day), and a misfire.

 

Did you make sure all air is out of system? Heater core could be air locked, happened to me once. I did away with electric senders and put mechanical oil and water temp gauges in mine . Don’t trust senders even if they are new. I also put a 180 degree t stat in mine

 

The heater blows hot, so I don't think the heater core is locked up? I tried to bleed the system as much as possible, and I figured any small bubbles would work themselves out through the overflow. I was able to bleed the system with no thermostat easily, but it doesn't want to run with the thermostat in.

 

One good, and easy, way to get the majority of the air out is to park it on a decent hill, nose high, so that the radiator cap is the highest point in the system. Loosen the cap so that it directs overflow into the tank, and fire it up. Let it get good and warm, with the thermostat in, and the heater temperature control to max hot. Any air flowing around the system will bubble out the cap, and into the overflow tank, and thus overboard.
After about 30 min of running it, shut it down. Put the radiator cap on tight, like normal, careful, it will be HOT, and when it cools down, it will suck the water back in from the tank. Once it's cooled down, pull the cap and check the water to be sure the radiator is full. Fill the overflow tank to the line marked on it.

Something to remember is that the design of the system has a small defect. Because the water cooled by the heater core, and it's associated plumbing, flows back into the system just before the thermostat. It can hold the thermostat closed until the engine's water gets pretty warm. Mine routinely goes to 3/4 or more on the gauge, however accurate THAt is, before the thermostat opens. It's mostly a problem in the winter, when I run the heater from the beginning. During the summer, with the heater set to max cool (no flow through the core), it hardly gets to 1/2 before the thermostat pops.

I've found a little trick, that works for me, is to, when the temp starts to get up there, before the thermostat pops, is to slide the heater control to full cold for a minute, until the thermostat pops, and then go back to what you want. The gauge will drop when it pops, then go up a ways, then drop, and so on, as the thermostat opens more or less, hunting for balance. After a few cycles, it all settles on whatever temp it is designed for. When using the heater, it will run warmer, like at 3/8 on the gauge, vice 1/4 when not using the heater. Again, it's that cold (relatively) water from the heater core, making the thermostat close down a bit more than if it weren't running water through the heater core.
Don't be fooled by the gauge, either. If you suspect it's getting too warm, check with an independant, third party, temperature gauge. Those infrared, point-n-shoot type are the best. Watch it, and see if it really IS overheating. Not getting a little hot, but truly overheating. The thermostat housing is a good place to do this.
Remember that if you pull out the thermostat entire, or it's guts, the engine will never warm up properly, so yeah, the upper hose might get warm, but the radiator will stay cold. The cooling system is working at full bore, from the engine's start. It's working too well, essentially.

Good luck to you!
Pat☺

 

Thank you for the detailed reply!

This is how I've been (trying to) bleed the system:



Regarding the heater cooling the water down too much before getting to the thermostat, I thought that could have been an issue, and bought the dual stage Toyota thermostat that allows it to open at a cooler temperature. Even with that dual stage thermostat in, the upper radiator hose doesn't get hot.

I will try cycling the heater a few times and also use an infrared thermometer pointed at the head and thermostat housing and update the thread. I'm thinking (and mentally preparing) for it to be a head gasket issue, though.

 

Maybe I have just been lucky, but I have never had a problem bleeding my cooling system with the Spill-Free Funnel, even with all four wheels on flat, level ground.

It seems like coolant just isn't flowing like it should, and removing the thermostat is just enough to get the coolant flowing enough to circulate. You probably have a blockage somewhere.

 

I don’t like the shortcut of doing the timing chain without pulling the head. I’m sure many here have done it without a problem, but I’d never do it. I’ve seen too many problems, though typically it’s oil leaks.

what did you use to seal the timing cover back to the block?

 

I used Toyota FIPG. I haven't had any oil leaks in the 250 miles I've driven it.

 

The Fipg might be the problem. It could have squished and have partially blocked the coolant passages in the cover.

I only use the engine fipg on the oil pan. Pretty much every other mated surface has a gasket, either paper or rubber. Gasket Cinch works well with paper.

 

I thought the timing cover area doesn't have any coolant passages on the top edge where it meets the head? Or could the FIPG have been pushed further in and blocked something? The Haynes manual I have says to apply a little bit of FIPG on the edges of the timing cover even when replacing the head gasket.

Either way, I will probably end up removing the head and timing cover at this point to see if I can tell why it's overheating.

 

Well, that brings up some interesting speculation.
My post just a little while ago was asking about what was used to seal the cover to the engine block, not the head. And there are major water passages where those surfaces mate; inlet/outlet for waterpump. I was wondering if a rtv sealant(or FIPG) was used and it got into one of those passages.
But now the speculation. FIPG is pretty thick. It's designed to function as a gasket as much as a adhesive sealant. I've seen where those who leave the cylinder head on during a timing chain replacement will loosen the head bolts a little bit to be able to pull the timing cover out without totally trashing the headgasket. Now, if FIPG was on the top surface of the timing cover it might be acting as a shim; compromising the headgasket seal. It could be ever so slightly lifting up the head and preventing a good seal at cylinder head to block.

Regarding the info in the Haynes manual and FIPG at the head. The FSM does reference FIPG, but in a very small capacity. Imagine you have the timing cover installed and torqued, and are now ready to drop the head on. The FSM instructs you to put a dab on the seam where the cover meets the block. When I installed the head I put a swipe of FIPG there, forced it into the seam to prevent oil escaping, and wiped off most of the excess. Then I put the headgasket on.
I don't see how that would be possible if the head was already installed. I'd probably just be generous with the gasket cinch when the timing cover is installed and let it go at that.