On a recently overhauled Hino Ranger 15b engine air bubbles under pressure in radiator and expansion bottle, engine still cold. Cylinder head skimmed and gasket replaced. What could be the problem?

could be a blown head gasket. suggest getting a pressure test done at a radiator specialist type auto repairer . To confirm if pressure is building in your radiator system from escaping exhaust into the radiator system via a blown head gasket in engine.
Thermostat would cause over temperature not bubbles.

Blocked cooling system most likely a stuck thermostat. The coolant is not circulation therefore not getting to heater core. Replace thermostat and it should be fixed

Hi There, How about letting us know your given name, seems friendlier when answering your questions? Okay the problem your friend is having can be caused by something very inexpensive, the radiator cap, or as expensive as a replacement cylinder head. I suggest having the pressure cap tested which means using a cooling system test kit. If the release pressure of the radiator cap has become too low, coolant will be expelled. Also have the radiator tested. If there is a pressure drop look for where the leakage occurs. Other common places of leakage are from core plugs on the engine block and the water pump. Leakage from the pump is many times only evident with the engine running, but be careful only to observe and not to touch anywhere dangerous. If there is a pressure drop but with no evidence of leakage from the parts already mentioned but no leakages are evident, check inside the cabin to be sure that the leakage is not from the cabin climate control. Pressure should be maintained for at least fifteen minutes a little above the pressure stamped onto the radiator pressure cap. If all else fails it is time to suspect the cylinder and cylinder head gasket. If the cylinder head gasket is blown it can sometimes result in a mixture of oil and coolant, evident from the changed colour of the engine oil, but can also leak into the cooling system and result in the symptoms you report. If the engine is petrol with an alloy head, skimming and a replacement of the gasket will usually sort out the problem. If it has a diesel engine with a cast head, the head may be cracked, requiring the cylinder head replacement. Regards John .

I shouldn't be blocked because it is pretty new. The systems are usually good for 10 yrs or so before they start getting gunked up. I would think it is either the electric fan or the fan clutch (whichever you have) could be out and it isn't cooling the engine. Also, you could have air in the system which could cause the rest of the coolant to not circulate. Check for an air bleeder valve near the top of the engine, usually near the thermostat housing.

Sorry almost certainly your head Gasket, sound like a break between a cylinder and the water jacket - hence the bubbles.

I agree with Mike, but suspect you already have a measuring device to know the pressure is excessive. You should get the cap checked first.

But additional pressure that keeps coming out of the radiator above the release limit of 14-18 lbs is probably due to escaped compression from the engine cylinders. You will see bubbles inside the radiator while the engine runs.

Sometimes you will get water in the cylinder after the engine sets under pressure, but not always. Your engine works at about 140psi in the cylinder more or less. The radiator at 14-18 psi. A leak in a head gasket may take more than 14-18 psi to leak. So the leak acts like a one-way valve shoving air into the cooling system. Since the cooling system loses pressure as it cools, the water may not flow back into the cylinders when the engine is not running.

This is sometimes indicated in a cylinder bleeddown test where high pressure is shoved into the cylinder. Bubbles may be observed in the radiator from escaping air. Otherwise a compression drop in a cylinder may as easily be due to bad rings.

I hope my solution is helpful.

You might have a head gasket issue still. You should not see any geyser out of the radiator with cap removed, nor continuous bubbles if you start the engine up cold. A random bubble is not a concern.

If you start it cold with radiator cap removed, you should should not have any coolant being forced out the open cap location. If you do- even a small amount when cold means there is combustion chamber pressure entering the cooling jacket, and it will not always reveal in the oil pan when the leak occurs outboard of the oil gallery locations. A continuous stream of bubbles is also an indicator. Normal thermal expanision will occur as engine heats up. If you had the small hose that tapped off of one of the heater lines, and you simply plugged it or otherwise removed it to save some money on a radiator- that in itself can be the problem- that small hose bled air out of the heater core and out of the head so there would not be a need to "burp" the system of air. If you did not have it initially, your truck did not have that hose, but you might try burping it of air to make sure you do not have a pocket of overheating in one cylinder of the engine,

Normal running pressure is 16 PSI when hot, any more than that will force coolant out of the side tank and into the reservoir. Some of that expansion is normal.

Unless you have low PH water or serious galvanic corrosion going on elsewhere in the system, you should be seeing more than 2 years of service life out of a radiator.

With a normal engine you should be able to run at idle with the cap off, and provided there is room for thermal expansion initially, you will be able to watch the flow begin as the thermostat opens. All that should happen if there is not adequate room for expansion, is the coolant simply rises and overtops the radiator cap location.

You could have an airlock still in the system. Run the vehicle at idle and squeeze the top and bottom radiator hoses with the expansion bottle cap removed. Add fluid gradually to it keeping it under the full marker. The bubbling is super hot air caused by air trapped either in the engine block, or top of radiator. A little tip while doing this, have the heaters on in the car and on high heat with the fans running at high speed. If you notice the engine getting warm and the heating in the car stays cold, the airlock is going to need a bit more work. Eventually if you have replaced the head gasket correctly the air lock with come out. Hope this helped...

There's many causes of overheating (on all cars..).
The first and most obvious thing I would do after checking the coolant level in the radiator expansion tank was at the maximum level, would be to check for coolant leaks while the engine is running with a 'few revs' on a warm engine.

Hoses can split internally and also become soft and collapse internally through age. When this happens the hose becomes blocked and prevents the coolant from passing through easily. If a hose feels 'soggy'/soft and is easily squeezed flat by hand, it's suspect.

Coolant can also leak from the heater hoses, the heater unit, the bearings/seal on the water pump and of course the radiator. Nor is it always easy to see a leak let alone find it. If the in-car heater unit is leaking the carpets may be wet at times and sometimes, the windows may mist up when the car is standing - this is the coolant condensing on the interior of the glass.

Ok... you can't see any leaks while the engine is running. Is the car losing coolant when it stands? Or is it losing coolant when the engine is running? ( a split hose may only leak when it is pressurised with warm coolant) Or is it just losing coolant when it overheats?

Remove the cap from the radiator expansion tank when the engine is cold. Make sure that the water level is at maximum. Leave the expansion tank cap off. Leave the car standing overnight and next morning look at the coolant level. If it has dropped there's probably an unidentified leak somewhere. If the coolant level hasn't dropped, it points towards a problem that is caused when the engine runs.

With the expansion tank cap still off (get a flashlight to help you) start the engine and peek into the expansion tank. Watch what happens to the coolant (though do keep your face out of harm's way). As the coolant begins to circulate air bubbles will probably appear within the coolant. This is quite normal - air is 'bleeding out' of the coolant as it circulates. The air bubbles should stop after a couple of minutes.

As the coolant warms it will rise up in the expansion tank (keep your face out of the way ..). If the air bubbles continually appear or, there's a constant and continual stream of bubbles or a 'violent bubbling' then this may point to problems with a warped/cracked cylinder head or leaking head gasket (or both).

A defective cylinder head/gasket can allow exhaust gasses to be pumped into the water jacket (the coolant system) simply by the compression action of the pistons. Just like a hypodermic needle can inject air into your bloodstream. When this happens - pressurised exhaust gasses being forced into the cooling system - the cooling system itself becomes pressurised.

The coolant itself can find its way into the cylinders where it is vapourized and pumped out of the exhaust along with the exhaust gases. If you can't find any leaks - the missing coolant may be going out of the exhaust as steam (though you may not see any steam as such). A classic sign of cylinder head/gasket problems is overheating. Check your oil - if there's a yellowish/creamy mayonnaise/sludge that's another sign of head problems. The sludge is caused by coolant finding its way into the oil.

No leaks, no bubbling expansion tank - and if you're happy that there isn't a head/gasket problem, turn your attention to the radiator, thermostat and water pump.

With age, cooling fins on the radiator can corrode and crumble away, reducing its cooling ability. Whilst coolant still passes through the radiator it isn't being cooled sufficiently. Check the condition of your radiator. Radiators can also suffer from an internal blockage. With a warm engine that is switched OFF, feel the top radiator hose - it will be hot. Then feel the bottom radiator hose. If the bottom hose is cold it indicates that coolant is not finding its way down/being circulated maybe due to a radiator blockage or failed thermostat. Flushing may cure blockages.

A thermostat can fail in the 'closed' position. When this happens coolant is prevented from getting into the radiator via the top hose. The coolant in the block then overheats causing the temperature gauge to hit red. The thermostat is located (usually - it depends on make/model variations) on the cylinder head where the top radiator hose joins. They're very easy and cheap to replace.

The water pump can leak water when the bearings/seal fail. Coolant that slowly drips onto a warm engine soon evaporates making detection difficult. Way back, some water pumps had plastic impellers (perhaps they still do). The plastic vanes on the impellers used to wear away with age and use, leaving a spindle spinning uselessly in the coolant - not pumping it. Think of an airplane with a propeller. If the propeller blades wore away the 'nose cone' would just spin uselessly and no air would get moved ..

Before jumping to any conclusions and replacing parts unnecessarily, get a workshop to look at the car. A workshop will be able to test the coolant for exhaust contaminants within minutes (or pressure test the coolant system. If there's contaminants present - there's a head problem. No contaminants present - the fault lies elsewhere.

Back to the cylinder head:
It's a 2-3 day job to do the work yourself. A cylinder head must be skimmed prior to refitting. Refitting an unskimmed cylinder head back onto an engine cures nothing.

Years ago, here in the UK, there was a liquid additive called 'head weld' (and one for the radiator called 'radweld') which provided a TEMPORARY get-you-home fix. Head-weld was a liquid added to the coolant system. It contained fine particles in suspension ... these particles were carried to the crack/leak in the cylinder head and formed a 'dam' that was held in place by the water pressure until they (the particles) hardened.

Recently I noticed an advert for a product called 'steelseal' - here in the UK. The advertising blurb claims that it uses new technology without particles to form a permanent fix for cylinder heads/gaskets. It's a clear liquid that you just pour into the cooling system and then run the engine until its fixed. I've never tried it. At around 45 dollars a bottle it isn't cheap, though if it does what is claimed then it's a hell of a lot cheaper than having a cylinder head/gasket fixed. No doubt there are similar products on the shelves of car accessory and parts shops near you.

Hi,

In its simplest terms, the head gasket is the spacer/insulator between the cylinder head and the engine block. When the piston (in the block) moves upward to compress the air/fuel mixture (against the cylinder head), tremendous pressure develops inside the combustion chamber. The pressure will find any easy means of escape to expand. If the gasket is defective, the pressure will pass through that gasket and enter the water jackets (where the collant flows through). The pressure/air bubbles will ride the coolant flow and eventually end up inside the radiator and would then be visible as you have posted.

Incidentally, the gasket may be OK but the cylinder head could be warped and the same fault would also be exhibited. This is especially more so on aluminum heads.

Both the gasket problem and/or the warped cylinder head could have resulted from a prior overheating problem.

Corrective procedure on the air bubbles would require top overhauling wherein only the cylnder head is removed. Of course once removed, your mechanic would be able to inspect the pistons and its sleeves and could decide if a general overhaul is required or stick to the cylinder head work. A top overhaul also requires cylinder head gasket replacement.

Unto the overheating problem, you may want to check the water pump, thermostat, fan, fan relay and fan clutch. It may also be to your added advantage if you would have the radiator flushed/cleaned as well as the water jackets. Some mechanics especially in warmer regions opt to completely remove the thermostat and permanently wire the fan to always be on.

Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards.

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