1HDT Coolant into Overflow - What am I missing?

[mudgudgeon]

I might have missed it, but has radiator cap been suggested?

My 1hd-t puked coolant a couple of times, but it was intermittent. I thought i had a cracked radiator tank, but couldn't confirm the source.
Eventually I was able to see the overflow bottle overflowing and coolant ran down the radiator and was dripping to the ground near the bottom radiator hose.

A new radiator cap fixed it for me. Coolant was pushing into the overflow tank, which is normal, but was not getting sucked back into the radiator, but normal.

After fitting a new cap, I never had it happen again.

This happened early in my owning this vehicle, and I later turned up the wick on fuel and boost etc and never had an issue again.

 

[perrobravo]

I might have missed it, but has radiator cap been suggested?

My 1hd-t puked coolant a couple of times, but it was intermittent. I thought i had a cracked radiator tank, but couldn't confirm the source.
Eventually I was able to see the overflow bottle overflowing and coolant ran down the radiator and was dripping to the ground near the bottom radiator hose.

A new radiator cap fixed it for me. Coolant was pushing into the overflow tank, which is normal, but was not getting sucked back into the radiator, but normal.

After fitting a new cap, I never had it happen again.

This happened early in my owning this vehicle, and I later turned up the wick on fuel and boost etc and never had an issue again.

Thanks for commenting @mudgudgeon . Not sure about others, but the radiator cap is where I started to try to fix this issue. I tried a couple different new OEM caps, an aftermarket cap, then yet another OEM version that came with the new radiator. I envy the success of your Occam's razor-style solution! No need to make things more complicated.

As mentioned above, I have all the parts to pull the head and see what I find, but still haven't dug in. I started the truck for the first time in many months to move it to my new shop space (the next building over) and it fired right up without issue. It would be so easy to ignore the issue and just keep adding coolant. However, I doubt that would be good for the long term health of the engine. And I'd have $1000 worth of ARP studs, various gaskets, etc. that would go to waste!

 

[bj70bc]

I would be going after the block and head flatness and also the RA of the head and block deck as the first culprits not allowing the head gasket to seal completely.
Mls gaskets need a pretty smooth RA (and of course flatness) to seal right
I had this issue on my 3b when i redid the head, and my (aftermarket) gasket was too thin by a hair and the block deck RA was too rough. After sorting both out it sealed well and pushes around 20 psi

 

[cmjtaco]

@perrobravo I was reading on the Aussie 1hd Facebook group about the "pushing coolant" issue, which seems to be common. one guy mentioned that it could be the locating dowel relief in the head not being deep after a resurfacing. The thicker gasket should compensate of course. Have you looked into it?

 

[bj70bc]

@perrobravo I was reading on the Aussie 1hd Facebook group about the "pushing coolant" issue, which seems to be common. one guy mentioned that it could be the locating dowel relief in the head not being deep after a resurfacing. The thicker gasket should compensate of course. Have you looked into it?

good call,
you could also burn down the locating pin on a sander...

 

[sebaguerow]

I have kind of the same issue with my 1996 manual 80 series, spit coolant after a long trip but only if I drive over 80mph, but after it cools down the radiator sucks the coolant again, maybe the 1.1bar radiator cap helps ? Or maybe the fan clutch ?

 

[veiloctane]

Won’t hurt to do another block test to be 100% sure exhaust gasses are not pushing it thru and try radiator cap.

 

[mudgudgeon]

I have kind of the same issue with my 1996 manual 80 series, spit coolant after a long trip but only if I drive over 80mph, but after it cools down the radiator sucks the coolant again, maybe the 1.1bar radiator cap helps ? Or maybe the fan clutch ?

View attachment 3717544

Spits coolant as in, it spills out of the overflow bottle?

 

[veiloctane]

Maybe no issue it’s just the over flow overfilled?

 

[dirtyboots]

For what it’s worth, a dribbling of small drops around the rad cap, and a leak (as pictured) from the overflow. If I keep it under 15 psi no issues. For this engine I have to guess the additional boost / floating is the issue. Interested to see the OP’s re build with ARP studs. @perrobravo which stud kit are you using? Neighbor races Cummins and I guess studs going through the block essentially clamping the head and block together with nuts on each end of the stud is standard for high HP diesel.

 

[veiloctane]

I

I have kind of the same issue with my 1996 manual 80 series, spit coolant after a long trip but only if I drive over 80mph, but after it cools down the radiator sucks the coolant again, maybe the 1.1bar radiator cap helps ? Or maybe the fan clutch ?

View attachment 3717544

I like this radiator any modifications needed to fit?

 

[sebaguerow]

I

I like this radiator any modifications needed to fit?

no modification is the common one on ebay!! the hoses are from a local dealer here in Paraguay, but I think they are on ebay too

 

[sebaguerow]

Spits coolant as in, it spills out of the overflow bottle?

out of the overflow bottle, the cap in the photo said that hould 0.9 psi but it only hold 0.3, I change the cap to a 1.1 from thailand and now its working just fine

 

[DivByZero]

I have experience with this exact issue on my HZJ80 about 6 years ago. In my case, it was a cracked head (from a previous severe overheating event). I didn't do the work in this case but I inspected the head when it came off, and it had a few good cracks in it. No pics, sorry. It seems air/exhaust was being forced into the coolant channels, but only when the engine was working hard enough for heat expansion to occur at the right places.

I could not reproduce this issue sitting in the driveway. It passed every test, compression, exhaust gases, no white smoke, etc. Local mechanics suspected gasket/head problems but could never prove anything wrong from tests. I have a theory you even needed the thermal differential of cool area rushing on the outside of the head at speed with heat generating inside when working hard to open those cracks up, while when sitting stationary they'd close again as the metal temps became more uniform. I drove with these cracks for about a year, until they widened more and the coolant loss became more severe and more frequent. I drove 3000km round trips between states in Australia with the engine like this, and at first I'm topping up coolant every few thousand kms. Over time it worsened and eventually I'm getting a visible trail of green and losing a few hundred mls every trip to/from work. Still passed all the tests. Pulled the head, and there were three or four good cracks in it!

Lesson here is, don't trust any tests. If you've run out of other possibilities, plan to pull the head and inspect. It's the only way you'll find out for sure.

 

[SNLC]

I have experience with this exact issue on my HZJ80 about 6 years ago. In my case, it was a cracked head (from a previous severe overheating event). I didn't do the work in this case but I inspected the head when it came off, and it had a few good cracks in it. No pics, sorry. It seems air/exhaust was being forced into the coolant channels, but only when the engine was working hard enough for heat expansion to occur at the right places.

I could not reproduce this issue sitting in the driveway. It passed every test, compression, exhaust gases, no white smoke, etc. Local mechanics suspected gasket/head problems but could never prove anything wrong from tests. I have a theory you even needed the thermal differential of cool area rushing on the outside of the head at speed with heat generating inside when working hard to open those cracks up, while when sitting stationary they'd close again as the metal temps became more uniform. I drove with these cracks for about a year, until they widened more and the coolant loss became more severe and more frequent. I drove 3000km round trips between states in Australia with the engine like this, and at first I'm topping up coolant every few thousand kms. Over time it worsened and eventually I'm getting a visible trail of green and losing a few hundred mls every trip to/from work. Still passed all the tests. Pulled the head, and there were three or four good cracks in it!

Lesson here is, don't trust any tests. If you've run out of other possibilities, plan to pull the head and inspect. It's the only way you'll find out for sure.

The one I dealt with I believe was the same except the cracks are in the block.

Cheers

 

[perrobravo]

OP here.

Procrastination got the best of me, but I'm finally digging in to find and hopefully fix the root cause of my issue: Coolant being pushed into and out of the overflow reservoir under load/boost.

Got the intake and exhaust manifolds, fuel lines, timing belt, etc. off. Then carefully loosened all the head bolts per the FSM. Then, when pulling the first bolt at the back of the engine, the washer fell off and of course into an oil passageway and down into the abyss. Pulled the head and poked around with a magnet and using my borescope to no avail. Fearing the washer was caught up somewhere bad, I pulled the oil pan.

Several hours later...

With that time-consuming mess behind me, I started taking a closer look for signs of the original issue. Maybe I'm seeing things, but it looks like combustion gasses have been sneaking into the coolant in a couple spots at the back of the engine.

Smoking gun supporting the theory that the head was lifting under high boost?

I have since cleaned up the block and head, checked both with a straight edge a dozen times, looked for cracks in the cylinders and elsewhere and don't see any other potential issues.

With the oil pan back on, next up is putting the ARP studs in and muscling the head back in place. Fingers crossed.

 

[perrobravo]

Many thanks to all who have posted here and provided tips and ideas! Some good news (with fingers crossed).

Installed the new 5 notch head gasket, head, and a set of ARP studs. Filled with fresh coolant and oil and the engine fired right up!

First start video here

Making progress

5 notch goodness in place

Decided NOT to use this "new" OEM radiator cap

On the first and subsequent drives, there was a disturbing amount of bluish-white smoke from the exhaust, mostly on deceleration, and even a random big puff of smoke. After some poking around and reading through the comments posted by @Loober in this thread, I started to question whether I'd changed the valve stem seals.

Blackstone labs didn't find anything suggesting a problem in oil or coolant analyses.

I used the same machine shop @Loober did (MJM in Escondido) and dug up my old records showing they had in fact been replaced...3 years ago. Grasping at straws, I thought maybe all that time sitting idle could have dried them out a bit, so I poured in a bottle of AT-205. After driving maybe 50 miles the smoke completely went away. Awesome. Getting close to declaring this a success.

I'll continue to closely monitor coolant levels to make sure the head gasket was really the root cause of what started this thread, but so far so good...so fingers crossed!

Back on the road (well, the parking lot at least)!

 

[perrobravo]

Another follow up and some potentially interesting findings.

TLDR: Used a no-spill funnel tool to get coolant level above heater valve...got bubbles out...no more issues.

On several drives, coolant continued to push into the overflow. Starting with the radiator full and at the low line on the reservoir when cold, coolant levels rose to or slightly above the high line after driving around. After cooling overnight, the reservoir would stay at the same level whereas the radiator would be down an inch or so lower than when I originally filled things.

Working on the theory there must be some air remaining in the cooling system which could prevent building enough vacuum to draw coolant from the reservoir, when cooling, I decided to get one of those no-spill funnel filling tools. What could it hurt? Note, I'd previously used a vacuum filling system several times and flushed the cooling system thoroughly.

With the front wheels on ramps and the funnel in place, I added 800ml of coolant, enough to get the coolant level above the heater control valve near the firewall. Then, I turned on the heater, and ran the engine up to temp.

Suspecting the heater valve of trapping air, I tapped on the hoses with the engine running (around 1750 RPM). A few seconds later, bubbles would come up the no-spill funnel. I repeated this several times over 30 minutes until no more bubbles would appear while squeezing the upper radiator hose after tapping the heater hoses circled below.

Tapped here release bubbles

The coolant level in the funnel went down to around 700ml, so down 100ml from where I started.

Since then, the reservoir level has remained at the low level when cold and the high level when hot. This seems to have solved things. Normal operation as far as I can tell.

So good. But this does raise several questions...

1. Did I really need to replace the head gasket at all? I saw witness marks that appeared as compression escaping into the cooling system (pic posted above), but no amount of testing proved this was actually happening.

2. Is vacuum filling really better than the much cheaper and easier no-spill funnel thing? Maybe in some cases, but not when there's a part of the cooling system higher than the radiator inlet?

3. Could this be the root cause for others who commented here about having the same symptoms? I hope so...this is far less painful than cracked heads, blocks, head gasket issues, etc. Certainly worth a try.

4. Where do zebras get their stripes? Probably irrelevant.

Will report back if things change, but after 500km expected coolant levels when cold and hot in the reservoir, I'm more confident than I have been that the cooling system is working as designed.

 

[OGBeno]

It so funny people spend so much time guessing when two very simple tests confirm whatever you want to know about your engine:

1. Compression test: compare your numbers to FSM specs. Either within specifications or not.

2. Leak down test: tells you if you have exhaust gases going into your cooling system

That’s really it. These things are all really dumb machines; they either work correctly or they don’t.

Toyota has suckered us all by building interminably robust assemblies that continue to live even when they should have died; and we get suckered into false analysis paralysis.

Always start with the simplest things with these old ancient agricultural power plants.