Technical > Four Wheel Finesse
Bring 'Em Back Alive - Part 3
Engine Cooling Systems
by Jim Allen
A vehicle can overheat for many reasons, not the least of which is a thrown fan belt. No water pump equals no cooling. At least replacing a belt is relatively simple, even when it happens on a rather tricky slope.
The emergency repairs outlined in this story are not offered as permanent, or proper. Combine them with common sense, judgement and use at your own risk.
We continue our discussion of mechanical “McGuyvers” by talking about engine cooling system problems. These are one of the most common general engine difficulties on the trail. Any engine can be overwhelmed by enough heat... even if there is no apparent problem.
Always start by lessening the heat load. Turn off the air conditioning and run in a lower gear to rev the engine up and spin the fan and water pump faster. If your rig is an automatic, it will usually have an oil cooler in the radiator. The added heat from a hard-worked automatic can overwhelm an already strained cooling system. You can lessen the cooling load on the radiator the same way as above... gear down. It reduces torque converter slippage, the major heat producing element in an automatic trans. More rpms and/or less load is the way to reduce that slippage, as well as lessen the workload on the engine.
Other tricks include the old standby, turning on the heater. What is a heater core but a tiny radiator? If your rig has A/C with an auxiliary electric fan, you can use it as a supplemental or substitute fan by jumpering it to run with the A/C off. An occasional dousing or spray of water over the front of a radiator, especially in hot, dry climates, will really help cool an engine. You can rig the washer pump to do that. The old start and stop trick works too. Drive till the engine gets close to the danger zone, then stop for a half hour or so, hood open, to let it cool and repeat until you get back.
Diagnostics and Temporary Repairs
First off, just because the gauge reads hot, it doesn’t mean the engine is overheated. Gauges and sending units can fail or read high. Without a secondary way to measure coolant temp, such as a radiator thermometer, this is a difficult call to make for a novice wrencher. An overly hot engine “talks” by gurgling ominously, running and sounding a little strange and smelling hot. Even if it’s not spewing like “Old Faithful.” It’s a hot oil, hot coolant, hot paint and rubber kind of smell. The heat coming from an overhot engine will sizzle your whiskers. It’s a “Zen Mechanic” kinda thing you will learn with a little experience.
If the engine is very hot, but not boiling over, it may boil the second you shut it off. Remember to never remove the radiator cap from a hot engine! Unless it’s actively spewing, let it idle a bit and pour water over the radiator before shutting it off. Then just let it sit and cool off for a while. Check the obvious stuff like loose fan belts, low coolant levels and for blocked airflow across the radiator. The airflow through radiators can be blocked by all sorts of stuff, from leaves and chaff, to fur, feathers or even ice and snow.
The two common ailments are low air flow or low water flow. If the air flow is not blocked, make sure the fan is working. An electric fan is obvious when it kicks on... or not. Most cut in at 190-210 degrees. If not, start with the fuses. Relays or temp sensors can fail, but you can wire across the related terminals to get them working. They all work a little differently, so research your setup. Some ‘wheelers rig a manual bypass switch that allows them to turn the fan on at will. Occasionally a fan motor will burn out or be ruined by water immersion and there’s not much you can do about that on the trail.
Mechanical fans with temp sensitive clutches can fail and let the fan freewheel. On a really hot engine with the engine off, the fan should not be easy to spin by hand. If it is, the clutch may have failed. I have seen guys couple fan clutches by various means, including putting bolts through them, but this is not always safe. You don’t want the clutch coming apart and sending the fan through your hood or the radiator.
Low water flow that’s not related to a plugged radiator or block is often due to a failed thermostat. In this case, drain (and save) enough coolant to get the t-stat out without dumping coolant all over creation. Not dumping coolant is an important environmental issue, yes, but also coolant helps your truck stay cool and you want it back! Water flow can also be impeded by old, spongy radiator hoses. They can partially collapse inside to block flow. Lower hoses can “suck” shut when the engine is above idle and reduce water flow. You can see this if you rev the engine up while you watch the hose.
1. If you have a leaking tube in the core, step one is to strip the cooling fins away from the area of the leak. |
2. Cut the tube in two at the leak, then roll the tubes back like a toothpaste tube, pinching the ends closed. |
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3. Many times a single pinch is enough, but you may need to do a double roll on the end of the tube for a complete seal. Pinch the ends tightly with pliers, but don’t tear them. Sometimes, this repair will hold full pressure and be leak free. Other times it may seep but stop leak may completely seal it. |
4. In the event of a spit hose, the old fix was to stitch the cut closed with wire (or fishing line then tape it with the best tape you have, which was usually electrical tape. Then came duct tape, which pretty much eliminates this step). Still, with a really bad split, you may still need to do this and you may not have duct tape. I saw a hose stitched like this and goobered up with RTV, and allowed to cure. It held. |
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5. Duct tape is one of the most important repair tools you can have. It can be used to repair a hose as shown, or for a thousand other purposes. There is a quality gap with duct tape and the cheap stuff won’t hold or stick as well. Some is really thin. Buy the really thick stuff that’s really hard to peel off the roll. |
6. A hose repair sleeve is the best way to fix a hose problem because when clamped, it’s a semi-permanent repair that will hold full pressure... assuming the rest of the hose is up to full pressure. There are several types of sleeves, some that are not up to high temps. Most auto parts stores have these splices. Buy the sizes needed for your rig and drop them into your spares box. They are a lot easier to store than spare hoses. |
Blown Head Gaskets/Cracked Blocks or Heads
There’s always the dreaded blown head gasket scenario to sweat over, or the even more dreaded cracked head or block. There are three main failure modes, the external leak, the internal leak where coolant leaks into the crankcase, or a combustion leak. The external leak is easy to detect and, usually, to repair. A stop-leak product will often stop it or slow it down, especially if you reduce system pressure as mentioned farther along.
An internal leak into the crankcase can be more difficult to detect and to deal with. Usually the oil emulsifies and turns milky. Sometimes you don’t even know it’s happening until your lifters start rattling or the oil light comes on. “Stop Leak” and reducing system pressure may work at stopping the leak, but the important thing is the oil.
It’s best to change the oil. The water tends to evaporate, leaving behind mostly the glycol products and they reduce the lubricating properties of the motor oil. Not many people carry enough oil to do a change, but if you collect some from everybody in your group, you may get enough. Don’t worry if it’s different brands or grades, as long as it’s motor oil.
Barring enough oil for a change, if you let the engine sit a while, the oil and water/coolant will separate. Sometimes this takes a long while. Sooner or later, you can remove the drain plug and let the water drain out. Water will come out first, but once oil starts running out, replace the plug. Don’t forget that you must remove and drain the filter the same way. Be sure to top off the level and change the oil ASAP!
A combustion leak is sometimes indicated by contaminated, evil smelling coolant and lots of boiling over. Other times, you’ll get an oily mess in the radiator. At the beginning, the combustion leak may be just bubbling carbon monoxide into the cooling system, aerating it and reducing cooling system efficiency. Later it will cause the engine to boil over, foam and even blow hoses or split radiator seams. Rarely will a radiator stop leak product stop a combustion leak because it creates too much internal pressure for them to work effectively.
If you can isolate the cylinder with the problem, a trick that may work is to remove that spark plug, ground the plug wire and disconnect that injector (if so equipped). That will reduce cylinder pressure and perhaps allow the stop-leak to work. Running on one cylinder less is better than having an engine that boils over once a minute. Never tried this one myself and I’d reserve this trick for a time where there is no better alternative... such as taking a strap.
One final thing to remember is that the silicone in coolant blowing into the exhaust will destroy or degrade the performance of catalytic converters and oxygen sensors. The more coolant you blow through, the more the chance you will ruin the cat and O2 sensors. It doesn’t take much to kill an O2 sensor and only a little more to kill a cat. The strap might be a cheaper alternative,
Ordinary Leaks
You can temporarily repair hoses in various ways. If it fails near the clamp, cut it off shorter and reconnect it. If it splits in the middle, the best fixes are those hose splice deals (see photo) because you can be 100 percent back in business at full pressure. Barring that, use duct tape, or even stitch or staple the split with wire or fishing line and tape or even glue. These latter repairs will not be up to full pressure.
Gasket leaks can be dealt with by using “Stop Leak” as a first shot, or you can remove the part and use RTV sealant to reseal it. In a situation where this is not practical, draining the coolant to below the level of the leak, cleaning the area around the leak and applying RTV to the outside may work... if you give the RTV plenty of time to cure. A seeping freeze plug will usually seal with “Stop Leak”. J-B Weld epoxy, or RTV, can be used for a major freeze plug blow out or leak.
Radiator damage is possible in the hostile ‘wheeling arena. In mild to moderate cases, a can of “Stop Leak” is the answer. In severe cases, you have to get more physical. A split tank or tank seam can be dealt with by applying epoxy, like J-B Weld. The area needs to be dry and free of paint and given plenty of time to cure. A core leak can be handled by snipping the leaking tube, or tubes, off and rolling up the cut ends like a toothpaste tube, as shown in the nearby pics, and pinching them shut. This kind of drastic work usually requires removing the radiator but it’s often a very successful repair.
If there is a “no sweat” part about common leaks, it’s that as long as you keep the engine full of coolant or water, you are OK. That might mean stopping every couple of miles to refill or having to scrounge water, but at least the engine isn’t toast as long as you keep it full. In a screaming emergency any water based liquid can be used, from fruit juice to soda, from beer to used beer. Ahem!
Reducing Pressure
Many temporary cooling system repairs involve having to reduce the system pressure so the repair will hold. The easiest answer to that is leaving the radiator cap loose. Expect some loss of cooling system efficiency and sometimes overflowing coolant. There’s a good answer to this also. I carry a 5-psi radiator cap in my spares kit and it’s paid for itself twice. In the case of an external head gasket leak, the lower pressure cap allowed the “Stop Leak” to hold (after it blew out twice at normal cap pressure) and it slowed a water pump leak to a manageable level. Best of all, it gave me back some of the lost cooling efficiency.
Shame on You!
If you venture out on a hot day with a plugged radiator, rusty coolant or a V8 swap with a 4-cylinder radiator, or any other neglect or poor engineering related problem, don’t expect much sympathy.