Horrible overheating issue

[Grappler]

Sounds like a small gasket leak for sure, which is the beginning of the gasket failing. The longer you drive, the more pressure (typically from a break between the combustion chamber and the cooling ports) is building up in the cooling system, giving you bubbles at first and push out of the overflow later. I drove mine like this forever before finally doing the whole thing -- I was in denial until it got steadily worse!

I never saw smoke, never had any real issue with running poorly - though it did feel sluggish, just the bubbles and the occasional overheat due to lack of coolant. This was what my gasket looked like when I removed it:




At this age, the failure seems like a feature, not a bug. If you fix the gasket, make sure to reference the site for all the other things that need repair to keep the cooling system in top shape.

[timsrv]

Hello all, I've got similar happenings with my 87' that I'm hoping you can give me some insight on. I'm able to drive it around the city with literally no issue, coolant does it's thing; pushes into the overflow then sucks back into the radiator after cooling down. However, after driving for about 2 hours (temp stays right where it should) coolant will start pushing out of the overflow and onto the ground. Not until the radiator gets low on coolant will the temp start climbing.

So I started by replacing the radiator cap and all hose between my neck and overflow tank. Coolant looks clean peering into it. It passed a combustion test although I do see small bubbles peering into the neck while running and revving. Just checked my plugs and they look as they should. No white smoke or coolant smells coming from the exhaust. Put a temp gun on the radiator and hoses to check for inconsistent temp, but all was good.

I'm convinced it's head or gasket related and I'll gladly do the job, but just want to be sure and rule out any other possibilities. Thx in advance! Jared

It doesn't sound like a bad gasket yet, but.........on these older vehicles, I can understand (can even agree with) just doing a head gasket to rule it out and make the van more reliable. And I'm not talking about only the head gasket. Pulling the head gives you an excuse/opportunity to service/replace everything that can become problematic over the years. Even if the head gasket job wasn't required, it will some day (these only last so long) and knowing it's new will ease your mind while on the longer trips.

That being said, doing a thorough job using genuine and/or quality parts can be a bit expensive and time consuming, so it will require some planning. If you go that route, I would recommend doing the following:

*Take the radiator down to a radiator shop and have it boiled out & tested. Follow the advice of the radiator specialist. If it tests good, you can re-use, but if you have some extra money now would be a good time to have a high efficiency core installed. If you're thinking of just going all-out, then search the site for "Ability Radiator" as there are some good threads on the subject.

*Replace the Thermostat with a genuine Toyota part: https://www.toyotavantech.com/forum/...n-s-thermostat

*Replace the clutch fan with an Aisin: https://www.toyotavantech.com/forum/...3762#post13762

*Replace misc coolant hoses: https://www.toyotavantech.com/forum/...=2052#post2052

*Follow the advice outlined in this thread: https://www.toyotavantech.com/forum/...ng-Head-Gasket

Here's a thread I made during the last major service I did to my van's engine. It's a bit more extreme than your situation, but it has some good information there you might find helpful: http://www.toyotavantech.com/forum/s...ngine-Overhaul. BTW, I did that when the van had 204k miles on it. I'm now over 265k miles and other than some unrelated issues & routine maintenance, that van has been trouble free (but I still open my hood every 2k miles to check/top off oil)

If you're on a limited budget, then I'd focus more on identifying and replacing only the part(s) responsible (or the ones that break while gaining access ). Good luck. Tim

[Beatrice87]

Sounds like a small gasket leak for sure, which is the beginning of the gasket failing. The longer you drive, the more pressure (typically from a break between the combustion chamber and the cooling ports) is building up in the cooling system, giving you bubbles at first and push out of the overflow later. I drove mine like this forever before finally doing the whole thing -- I was in denial until it got steadily worse!

I never saw smoke, never had any real issue with running poorly - though it did feel sluggish, just the bubbles and the occasional overheat due to lack of coolant. This was what my gasket looked like when I removed it:




At this age, the failure seems like a feature, not a bug. If you fix the gasket, make sure to reference the site for all the other things that need repair to keep the cooling system in top shape.

Thanks for all the advice and links! I bought my van almost 2yrs ago from a fellow in Nyc, that owner put a freshened up 4y in it that was professionally done. I bought it with around 20k on that motor and 200k on the actual body. Ran excellent until one hot day I was chugging up a hill and bam my temp spikes to almost red. I stopped immediately and noticed coolant gurgling out of the overflow and that my electric fans had stopped working. I can't imagine almost overheating it one time would damage a head gasket, that's why I was searching for a different cause. I've got access to a shop in two weeks, I'll keep yall posted on what I discover.

And @Grappler, did yours push coolant out the overflow then?

[llamavan]

I can't imagine almost overheating it one time would damage a head gasket

It absolutely CAN.

And, too, a slightly compromised HG can lead to "almost overheating" all by itself — ie, perhaps the damage was already done.

I understand and support the search to confirm what is going on — a head job isn't cheap or quick, and it would suck to pay for that or do it yourself and then discover the problem still exists. HOWEVER ... your van's coolant must be going SOMEWHERE, and a tiny HG breach will result in what you describe. Unless you can find where the coolant is leaving the water jacket OR some way that air is getting into the water jacket (causing temp increase due to inadequate cooling system pressure), the HG is the only thing left that makes sense.

Gwen

[Beatrice87]

Replaced my head this weekend and noticed my vacuum valve port on the new head is smaller than on the old. Anyone else run into this? I'm guessing I should use a brass reducer to adapt it, but I was having trouble figuring out the thread pitch on the new head.... thanks for the info in advance, always helpful!

[pryter]

Hi all, I'm having an overheat issue. I had a catastrophic overheat on a longish trip, that involved my water pump blowing up on the highway. towed the car home, replaced water pump (Aisin) fan clutch (aisin) thermostat (Toyota) radiator hoses (gates) and fresh coolant. that was 18 months ago and its run great ever since. a few days ago while driving it overheated, luckily close to home. I let it cool off and limped home. I just checked temps with an IR thermometer at idle. 120 on top hose 94 on bottom, 80 in the radiator and 300 on then engine head.

it seems to me like a circulation issue to me. v belt is fine and coolant looks clean. all the major cooling system parts are relatively new. I would love to hear thoughts on what might be going wrong?

[pryter]

I figured it out sort of. overheating was caused by a lack of coolant in the radiator (duh), but there was plenty in the overflow tank. I drained it, refilled it and the engine is running fine. I replaced the radiator cap but there still seems to be coolant boiling off and not returning to the system as it cools. I'm thinking there must be a pinhole leak that I'm not seeing somewhere in the overflow system that is preventing vacuum from sucking the fluid back in.

[trestlehed]

Check the hose that runs from your radiator to your overflow tank, it could be clogged with gunk preventing flow.

Also check the metal tube that comes off the radiator coolant filler assembly. The metal tube on mine was rusted/corroded
and clogged which prevented flow to/from the overflow tank.

[pryter]

mine is a bit rusty on the outside, but the hose is clear

[Burntboot]

Cooling systems, at least the flowing part, work on basic hydraulics theory.

So if you have a jug, filled with fluid, attached to a device that is also filled with fluid, assuming there is no air in the system then when the coolant expands, the jug should fill and when the coolant cools it contracts, (the reservoir level drops as coolant returns to the engine.)
When the coolant fails to return to the engine, it means there's a reason that the fluid can't flow back, either an air leak or a blockage.

Solving problems is about eliminating possibilities, nothing worse than introducing new variables when you're trying to solve one problem.

Was that new cap a new Toyota cap, something from the local supplier or a spare from your parts bin.
I only ask because the first option guarantees a known part
The 2nd one could be hit or miss depending on the ability of the parts guy and the spec's of that particular cap
3rd only works if you're SURE you know the status of your used part.

Another thing to ponder:
Old/hard rubber hoses will be less likely to be able to form a seal over a little corrosion (They are also incredibly cheap/easy to replace.)
Also note that that particular hose could feasibly leak air under suction but not leak coolant when under pressure, leaving no evidence of its fault.

[trestlehed]

I figured it out sort of. overheating was caused by a lack of coolant in the radiator (duh), but there was plenty in the overflow tank. I drained it, refilled it and the engine is running fine. I replaced the radiator cap but there still seems to be coolant boiling off and not returning to the system as it cools. I'm thinking there must be a pinhole leak that I'm not seeing somewhere in the overflow system that is preventing vacuum from sucking the fluid back in.

Sorry, also forgot to mention: Back in the day when I was having a terrible time trying to figure out where my coolant
was going (similar problem to yours) my mechanic was doing the "hose of death" project and discovered that the coolant outlet plate (on the back of the engine which is attached to the hose of death) was corroded and had tons of tiny pinholes in it. So the theory is that while hot and under pressure, the coolant was being forced out the pinholes and evaporating on the rear of the engine leaving no visible sign of a leak.

Something to check if you have no luck elsewhere.

[timsrv]

Another commonly overlooked problem is pitting/corrosion inside the filler neck where the rubber seal of the radiator cap contacts it. Check that surface carefully to make sure the raised ring in there is not compromised.

Pressure is a much more reliable way to move fluid than vacuum. Expanding coolant has no choice but to flow the path of least resistance. That path is typically through the overflow hose and into the recovery tank. After shut-down, as the fluid cools it contracts in the engine and that creates a vacuum. If there are no breaches anywhere in the system and your recovery tank hose is below the fluid level, it will suck it back into the engine. However, if there is even the smallest of pin-holes in the system, since air moves easier than liquid, it will suck air and leave the coolant in the tank. Tim