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Discussion Starter #1 (Edited)
Hi everyone! I have a Hyundai i40 2014 Tourer Diesel.

Recently, I picked her up from copart and I noticed that the coolant in the reservoir (not radaitor) was above the F. Also, the cars temperature would spike on sharp turns (roundabouts).

When I was driving back on the motorway, I stopped because it started overheating. When I opened the bonnet coolant was following out of the reservoir without me even opening it. So I left it to cool and got home.

when I got home I siphoned all the old antifreeze from the reservoir and I also used the drain plug in the radiator to remove all the coolant and filled it again. I also made sure the coolant is between the L and F. Mind you the antifreeze had no milky colour, So I don't think its a headgasket.

Since the car had no issues with overheating even on sharp turns. However, somehow and I have no idea how, I checked the coolant after a couple of days (engine cool), on level ground, the coolant reservoir had more coolant than I put in, above the F. And it seems like if I drive it, it will overfill again...

Can somebody please explain, what might be the issue? It seems like radiator is filling the reservoir.

Thank you all
 

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I would get a hydrometer and check your coolant and see if its within specs after it fills up with extra fluid. Seems to me like you have a severe internal mechnaical failure. Usually cracked block or head. Apparently block cracking is common on your vehicle. I would suggest a leak down test of the cylinders as well.
Usually this will consume coolant. However if cracked in the right spot in the engine you can gain fuel in the coolant. This is why i suggest a hydrometer.

Also if your engine truly overheated and didnt just build pressure in the cooling system due to the crack, you are likely already looking at new head gasket and some machine work.

Let me know what you get from the tests:
-Hydrometer Coolant
-Leakdown test cylinders
 

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Discussion Starter #3
I would get a hydrometer and check your coolant and see if its within specs after it fills up with extra fluid. Seems to me like you have a severe internal mechnaical failure. Usually cracked block or head. Apparently block cracking is common on your vehicle. I would suggest a leak down test of the cylinders as well.
Usually this will consume coolant. However if cracked in the right spot in the engine you can gain fuel in the coolant. This is why i suggest a hydrometer.

Also if your engine truly overheated and didnt just build pressure in the cooling system due to the crack, you are likely already looking at new head gasket and some machine work.

Let me know what you get from the tests:
-Hydrometer Coolant
-Leakdown test cylinders
Hello. Thank you for your reply. I will get tests done tomorrow as I have no testers.

But please can you clarify to me, so I can sleep at night, does this sound more like a failure at the radiator/ reservoir cap or the engine has catastrophic damage? The car has done 58,000 miles. It is very fuel efficient and I don't think it is feeding fuel to the coolant, otherwise, I would be burning more fuel.
 

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If after the engine has cooled, and your radiator is low on fluid but the overflow is full then yes it would be a cap problem. But extra fluid in the entire system has to come from somewhere. Which is usually a crack between cooling system and another fluid source.
 

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Hi everyone! I have a Hyundai i40 2014 Tourer Diesel.

Recently, I picked her up from copart and I noticed that the coolant in the reservoir (not radaitor) was above the F. Also, the cars temperature would spike on sharp turns (roundabouts).

When I was driving back on the motorway, I stopped because it started overheating. When I opened the bonnet coolant was following out of the reservoir without me even opening it. So I left it to cool and got home.

when I got home I siphoned all the old antifreeze from the reservoir and I also used the drain plug in the radiator to remove all the coolant and filled it again. I also made sure the coolant is between the L and F. Mind you the antifreeze had no milky colour, So I don't think its a headgasket.

Since the car had no issues with overheating even on sharp turns. However, somehow and I have no idea how, I checked the coolant after a couple of days (engine cool), on level ground, the coolant reservoir had more coolant than I put in, above the F. And it seems like if I drive it, it will overfill again...

Can somebody please explain, what might be the issue? It seems like radiator is filling the reservoir.

Thank you all
Have you blead it?make sure you put the heater on full, dont know if there is a bleed nipple going to the heater, then bleed the thermostat, and might be a nipple on top of the rad, if your heater blows out hot, there is no air in the system, had this problem on my daughters Dacia, don they above and all good, use the brown antifreeze mixed with distilled water.
 

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Blown head gasket or cracked head.
Combustion gases forcing the coolant out.
 

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Discussion Starter #7
Hi guys. Thank you all for your input! So a quick update...

The car had a lot of air in the system. I found that out by just trying to see if I can add anymore antifreeze to the system. I think this air came from my previous attempt of changing the coolant. Anyway, Since then, the car has been perfect temperature and the fluid acts like it supposed to. I.e. when hot it rises just above the F and when cold it goes back down between the L and F. The car doesn't lose or gain coolant.

Anyway, I didn't want to risk testing for head gasket leaks or block cracks with cheap tools (wasting my money). So, I booked her in with Hyundai at the start of August. Though the car is fine now, I want them to check the health of the engine with more sophisticated tools.

I will feedback on monday. Regardless, if I am selling the car as scarp or not. Thank you all for your feedback as well.
 

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Try replacing the radiator cap, had the same problem with a 1.4 Getz, 2nd hand buy, the cap was rated at 0,9 bar replaced with a 1,1bar and problem solved
 

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Hi guys. Thank you all for your input! So a quick update...

The car had a lot of air in the system. I found that out by just trying to see if I can add anymore antifreeze to the system. I think this air came from my previous attempt of changing the coolant. Anyway, Since then, the car has been perfect temperature and the fluid acts like it supposed to. I.e. when hot it rises just above the F and when cold it goes back down between the L and F. The car doesn't lose or gain coolant.

Anyway, I didn't want to risk testing for head gasket leaks or block cracks with cheap tools (wasting my money). So, I booked her in with Hyundai at the start of August. Though the car is fine now, I want them to check the health of the engine with more sophisticated tools.

I will feedback on monday. Regardless, if I am selling the car as scarp or not. Thank you all for your feedback as well.
Thats what I said, air in the system, best to try the simple things first, I would not take it to Hyandia first, they might make it worst, I'm not a mechanic, but a panel beater, and you have solved it, leave well alone. Some times common sense is better than computors.
 

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Discussion Starter #10
Thats what I said, air in the system, best to try the simple things first, I would not take it to Hyandia first, they might make it worst, I'm not a mechanic, but a panel beater, and you have solved it, leave well alone. Some times common sense is better than computors.
Thank you for your reply Keating. I don't want to be trolling, after I let the car cool down last night, this morning the fluid was above the F and no longer between L and F. However, no overheating issues or overflowing and the car has hot air blowing.

I will replace the radiator cap and coolant resovior cap. But I have no choice but to give it to Hyundai and see. Because I checked everything I could.

If anyone has input then I will be really greatful. Thank you all!
 

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Discussion Starter #12
Any white creamy crap on the underside of the oil cap?

Easiest way of checking if water and oil are mixing
No exodus. Not even signs or smell. I am hoping hyundai will answer up. I am putting my money on a failed radiator and or a thermostat.

I stopped in my garage the other day, after a long drive, I left the car running and opened the oil cap. White smoke kept coming out and if I put my hand over it, I can feel it blow the smoke hard on my hand. Is that normal?
 

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Oh, smoke can indicate piston rings are shot if excessive.

Not saying that is it BTW. How many miles are on the car?
 

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Discussion Starter #14
Oh, smoke can indicate piston rings are shot if excessive.

Not saying that is it BTW. How many miles are on the car?
the car is roughly 58000 miles. If they're piston rings shot, it still doesn't explain why the car coolant system is acting like this.

A stupid question, but do dealerships have tools for testing headgaskets?
 

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John51 has your answer. Radiator cap. A radiator cap has two different functions. One is to allow pressure to build in the radiator before acting as a "pop-off" or pressure relief when the engine is at operating temperature. Generally releases pressure at around 15psi +/- as the coolant expands with heat.

But, and this is where I believe your problem could be, it also has a secondary seal that allows a vacuum to form as the engine cools down and enables the radiator to draw fluid back into the radiator from the overflow tank. If that seal is bad you will be putting coolant into the overflow when the engine is hot, but will not draw it back when the engine cools. Had this happen on an XD series Elantra. It never overheated because we spotted it before it overflowed the tank.
 

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Hello, sorry I have been gone. Been busy.

If there is white smoke coming from the oil cap/dipstick tube while warm and none or less when cold, clear sign of a headgasket failure. If you have an aluminum head usually anything over 240 warps them badly. Will need decking (machine work) for the head to be usable agian.
Like everyone else has said, this are assumptions based on what we know.
You need a leakdown test preformed. And yes the dealer will have the equipment for that. It is not a device that is vehicle specific. Usually have a few adaptors for different sizes of caps and such. There is not too many.
 

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How did you get on mate? Was checking over my car to find an empty coolant tank and an oil cap in this state View attachment 449678
Hey Jed.
Last I recall this issue was resolved by bleeding the system of air through a vent.

Your oil cap appears fine. That white is the plastic itself. The white from a gasket issue is very white and foamy. Like toothpaste after u spit it out. And it will like to sit ontop or under the oil not within it.
 

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Hey Jed.
Last I recall this issue was resolved by bleeding the system of air through a vent.

Your oil cap appears fine. That white is the plastic itself. The white from a gasket issue is very white and foamy. Like toothpaste after u spit it out. And it will like to sit ontop or under the oil not within it.
Ahhhh cheers dude. I realised this after once I tried to clean it off, felt like a right tube! 🤡 Tbf they do make the cap mayo coloured tho!

When you say an air vent do you mean the actual blowers in the car (I thought I knew a secent about cars until today)

Funny enough the last time I ran the car I had the AC full blast as its been warmer here in Ireland. Topped up the coolant and took it for a 20 mile spin there with no change in coolant level
 

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Ahhhh cheers dude. I realised this after once I tried to clean it off, felt like a right tube! 🤡 Tbf they do make the cap mayo coloured tho!

When you say an air vent do you mean the actual blowers in the car (I thought I knew a secent about cars until today)

Funny enough the last time I ran the car I had the AC full blast as its been warmer here in Ireland. Topped up the coolant and took it for a 20 mile spin there with no change in coolant level
Im sorry for the late reply. Got busy with work.
By vent i mean that there is a bleeder somewhere on the cooling system. Id suggest just starting the car when cold with rad cap off. Turn heater on max and blower fan on max. Do not put the vents on defrost. Fill quickly until full. Wait a minute if it stays level in radiator. Fill the overflow to full mark and put caps back on. And you should be fine
 
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