Overheated 1HZ (1 Viewer)

[zuker81]

Hey folks, recently overheated my '91 HZJ73 1HZ motor like an idiot. Wasn't catastrophic (that i know of yet) but I seem to have lost a bunch of coolant and ruined my main seal.

I figured I had a radiator leak, but had the radiator tested and it was sound. Later in the process, i realized I'd never re-connected the water temperature sensor on the right hand side of the block. My assumption was this sensor only served the gauge on the dash, but now I'm realizing it might control other things related to fuel injection? Could this have been the reason for the overheat? And perhaps the coolant leak was a symptom of some other gasket failing due to heat?

 

[Tapage]

Fuel injection controlled by a sensor in 1HZ . .? not that I'm aware of .. actually we didn't get any ACSD in the 1HZ .. so no .. not that the cause ..

 

[roscoFJ73]

There is no relationship between the coolant sensor and the injection pump. There may be some between the glow system etc. So whats actually wrong with the 1HZ? They are pretty tough engines and the occasional overheat wont hurt them, depending on how hot it got and how long it was for.

 

[roscoFJ73]

Fuel injection controlled by a sensor in 1HZ . .? not that I'm aware of .. actually we didn't get any ACSD in the 1HZ .. so no .. not that the cause ..

I think the European models had them, it was part of their emissions equipment. The 1HZ all have the blanking cover fitted.

 

[roscoFJ73]

Could this have been the reason for the overheat? And perhaps the coolant leak was a symptom of some other gasket failing due to heat?

Has anything like the thermostat been changed. Can you tell us how it happened. Was it during a long drive of did it come on very fast going to work?
Is coolant leaking from somewhere?
The main causes of overheating are bad t/stats, blocked radiators and non functioning clutch fans.

 

[Tapage]

even with bad fan clutch a healty NA 1HZ, stock fueling it's hard to overheat ..

 

[zuker81]

Haven't changed the thermostat - On the way home from work, I parked and noticed quite a bit of condensation (or what i thought was condensation) dripping from just behind the bumper. It was a hot day, so I made a mental note to check the coolant level when i got home. Of course I forgot and drove it again later that evening. Pulling down my street to come home I smelled something funny, looked down at the water temp on the dash and the needle was pegged to the ceiling (this confused me later because i found the water temp sensor was unplugged-where is the dash water temp gauge getting its information??). I immediately killed the engine and coasted into the driveway (what luck). Popping the hood, the motor was smoking and I noticed a fairly catastrophic amount of oil coming out of the back of the block onto the driveway. The next day i pulled the coolant drain and got the rest out - it certainly wasn't full but had some left. I couldn't find a consistent leak when filling the radiator with water when still installed either. Radiator as mentioned tested soundly at the shop

A couple things have occurred to me:
1. The main seal could have developed a leak and the overheat could be oil related (doesn't seem terribly likely, no driveway evidence prior)
2. Coolant could have leaked from a different area (but why so suddenly?)
3. T-stat bought a one way and then heat caused various seals to also meet their maker?
4. General water pump fatality?

 

[ca18sean]

1. No. Oil leak won't cause an overheat. Lack of oil would cause engine failure but not due to overheating coolant.
2. Coolant leaks are relatively easy to locate. Go buy/rent a coolant system test kit. Advance Auto rents them, they allow you to pressurize the cooling system with the engine off to determine where the leak is.
3. Possibly, find the source of the leak first
4. Again, possibly but it's premature to come to that conclusion. I'd guess clutch fan before water pump. How easily does the fan turn?

You need to figure out where the coolant leaked out of. My knowledge is more 2H than 1HZ, but on my motor there are two temp sending units. One for the gauge in the dash, and one for the glow plug timer. The gauge is obviously still hooked up as it's reading, the glow one just determines how long to glow the plugs before starting.

Is the oil milky? Was the coolant oily? I'd also consider doing a compression check to determine if something internally has failed.

 

[zuker81]

Thanks a ton - I'll work on getting the system pressurized once I take advantage of the radiator being out to do some belt changes and t-stat for good measure. I haven't tried to turn the fan clutch but my understanding is turning it by hand may not always be a good indicator of its condition. Reading a bit more online, it appears the fan clutch is a very common failure point.

My understanding is removing the clutch and relubricating typically resolves that?

Coolant wasn't terribly oily, although I didn't really check closely. Oil did not appear milky, was regular sooty black.

 

[Tapage]

My understanding is removing the clutch and relubricating typically resolves that?

fan clutch ?

either you buy a new one stock, or rebuild / modify yours ..

gotta read here ( search 80 forum ) about fan clutch but basically it's a visco coupling with oil on it .. the heaviest the oil it have the more " engage " there is also a way to tune it for kicking sooner or later ..

 

[Loober]

I don't see how the main seal is connected to the overheating problem, that may be a totally separate issue unless something really catastrophic happened. If anything your head gasket would be the first to go, and may already have. Test to see if you have combustion gases coming into the cooling system first. Get it warm with the cap off see if you see bubbles or get a combustion gas test kit. If you do, your head gasket is shot hopefully nothing more. To have an overheat scenario like that is caused by more then a little coolant leak, definitely not because of a faulty temp switch. I was having similar symptoms which proved to be a bad head gasket.

 

[roscoFJ73]

4. General water pump fatality?

Unless the shaft has snapped, the water pump will be doing its job. The vanes are nylon and they will outlast all the other components on the pump.
If you look in the radiator, you will see coolant moving through if the pump is pumping.

Oil leaks are sometimes associated with overheating. Do you know for sure where the oil is coming from. Clean it down and watch it come back.
It may just be leaking from the back of the valve cover.

Radiator as mentioned tested soundly at the shop

What did they test it for? Because most of the time its just pressure tested for leaks. That will not show you if the cores are blocked.
Is your overflow bottle connected?
Does the coolant system maintain pressure once the engine is warmed up?

 

[roscoFJ73]

this confused me later because i found the water temp sensor was unplugged-where is the dash water temp gauge getting its information??

It depends on the intended market. The Australian models get the temperature from the upper coolant outlet. Youll have to ask someone else if yours is not an aussie model.

 

[zuker81]

@roscoFJ73 - reviving this thread as i'm getting ready to put a brand new head back in after year (what a saga!). After lots of thinking, I realized originally before the overheat occurred there were only two things that had changed - I'd flushed and refilled the coolant the week of, and I'd apparently left the glow plug sensor unplugged that day while driving.

Is there some world where the glow plugs would've stayed on due to this, and contributed? If it wasn't that, then it had to be the head gasket.

 

[FJBen]

@roscoFJ73 - reviving this thread as i'm getting ready to put a brand new head back in after year (what a saga!). After lots of thinking, I realized originally before the overheat occurred there were only two things that had changed - I'd flushed and refilled the coolant the week of, and I'd apparently left the glow plug sensor unplugged that day while driving.

Is there some world where the glow plugs would've stayed on due to this, and contributed? If it wasn't that, then it had to be the head gasket.

I would highly doubt glow plugs staying on could cause an overheating/blown head. If you unhook that temp sensor for the glow system, it just tells the glow system that it's super cold glow for maximum time then shutoff. IF your system is working right, if not it's possible it could run the whole time, but the worst case scenario I imagine here is burnout glow plugs.

I'd be more inclined to think you had an air bubble or something as you said you had flushed the coolant. This could cause overheating and possibly blown headgasket. Maybe the air bubble was around the t-stat, water didn't flow through? Maybe the flush dislodged some crud and block passages?
Either way, I find the timing of you flushing coolant and the subsequent overheating to be 100% related.

 

[mxtaco48]

Are you going to use any after-market temp sensors in the future? I overheated mine a couple of months ago and its going to the shop next Monday for the head to be inspected.

 

[zuker81]

Yes, my number one priority is to get a better warning system once it's all installed. I've been doing a lot of research but still haven't decided what my after market sensor will be, just know it will likely go in the coolant outlet spot. If anyone has suggestions of their preferred strategy i'm all ears.

@mxtaco48 i hope your head turns out to be reusable!

 

[mxtaco48]

I don't think I have a location at the coolant outlet spot without tapping a new hole. Mine is just rear of the oil filter.

What is the thread pitch/NPT of the coolant location?

 

[mxtaco48]

Longacre SMi Temperature Sensor 43500

E-commerce: Product/Category List.

www.longacreracing.com

 

[roscoFJ73]

Is there some world where the glow plugs would've stayed on due to this, and contributed

No, if they stayed on too long, it would have just burned them out and they would no longer function. Glow plugs do stay on after the engine starts at a lower voltage and can come back on if the engine temperature drops if you are in extremely cold conditions.
I cant see a connection at all between your coolant/head problem and the glow system.

Is it possible you did not get all the air out of the coolant system when you refilled it? If so, this may have caused the head to crack and and lead to your other problems. Overheating of engines can cause oil leaks.