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Very slow coolant leak

4703 Views 16 Replies 5 Participants Last post by  beef tits
Hi. I bought an 2003 Xterra model car back in 2005 (long story). It currently has 76,000 miles on it and has regular maintenance.

In March 2016, I went up a long hill and got stuck trying to turn around. I don't have 4-wheel drive and I may have pushed the engine a little too hard. I didn't notice it at first but a mile down the road the air-conditioning got warm. I looked at the temperature gauge and noticed it getting close to the top. I turned it off and a friend told me I was out of coolant. He went and poured some in. I wasn't sure what to make of it.

A couple weeks later I noticed a change in the level and a friend installed a new thermostat. There was no visible leakage under my car and the temperature gauge remained in its normal range. The A/C wasn't as cold as it should be (according to my friends) and someone decided to try recharging the Freon. That had no effect.

Without a low coolant sensor, I made sure to check regularly. In June 2016, I noticed it lower than the minimum bar. I went to store to buy coolant and refilled the container to a decent level.

It is now October 2016. People still complain my A/C isn't as cold as it should be and I just spotted my temperature gauge bouncing around as I drove up-and-down some hills. Yep, coolant was low again.

I have been told to check the thermistor (I guess the thermostat sensor), use dye, check coolant pressure, and check for air pockets. One guy told me to just buy a gallon of coolant every year since I don't drive that much. I'm hesitant to hand it off to some mechanic. I don't want to pay a lot of money but I do think I should fix it before taking a long trip somewhere. The only thing I can add is that the oil looks fine and I still get 16 mpg.

What do you think I should do?
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Seems like you are in a little over your head. Let's take a step back and let the facts guide us where we need to go.

First, you need to see if the oil and coolant are mixing. This is bad, since water is a lousy lubricator. If they are truly mixing, then this needs to be addressed quickly before more damage occurs (main bearings, connecting rod bearings..other important things).

The coolant, when mixed with oil, will not retain its green color. It will look like a chocolate milkshake. Check the dipstick and see if the oil is "frothy". Draining the oil will also help determine this. If the two are mixing, then it is likely a head gasket. Blocks usually don't crack, so although its possible, it's unlikely.

If the oil looks like oil, then they're not mixing and you can move on to where else it's going. I had a coolant leak in my xterra (actually a couple of times -- 3 to be exact). The first was it was coming from the intake manifold gasket. It led to a pervasive coolant smell, especially when I was running the heat. The second was from a bad water pump. Now the thing about this, was that it was actually a bad fan clutch. The fan was CONSTANTLY running, and it ended up beating the water pump bearings up and causing it to leak. The 3rd (and current) leak is from the radiator.

Here's my point. Follow the evidence. Some guy who takes 1 look at something and automatically assumes it's X should be more thorough and careful in his diagnostics. "it's probably the water pump" is a vague statement. What SPECIFIC evidence has led him to believe that? Has he seen leaking from the weep hole? Is the system not generating pressure? Has it been properly purged? How does he know it's not a clogged heater core or line? What the thermostat properly replaced? (backwards?). Has he performed a pressure test in the coolant system to see if there is cylinder pressure that's jacking the coolant pressure up? Has he performed a dye test, where by you can see visible (external) leaks? Where is the smell coming from? (coolant is very stinky). Is it blowing white smoke? (burning)

These aren't rhetorical questions, they are questions to equip you to discuss the problem with your mechanic and make sure he's not just putting in parts. There is a big difference between a parts changer and a mechanic. A mechanic will spend time diagnosing and properly vetting theories until the culprit can be narrowed down to a single or perhaps couple options. Only then, does he replace parts.

If you have questions, ask away.
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Mine turned out to be a cracked cylinder wall that allowed coolant to mix with the oil. The mechanic who did the work just replaced the damaged cylinder along with rebalancing the heads.

This doesn't make a lot of sense. Do you mean he welded and re-bored the cylinder? You don't really replace a cylinder, it's a hole. Or did he sleeve the cylinder?

Rebalancing the heads doesn't make sense either. Do you mean resurface?
At one point someone, somewhere tells you if an engine is supercharged. I never got that information and the people I talked to didn't seem to know either. I don't think I had one person tell me directly "This is not supercharged" until yesterday when I took it into the shop. No one could find it written down in any of the paperwork. It is entirely possible some of the people I talked to earlier assumed I would know and simply didn't tell me.

The mechanic will be replacing the water pump and intake manifold gasket. The dye in the coolant revealed puddles directly under the water pump. There were also puddles in several spots around the engine. Multiple people hinted at poor circulation since not all the hoses were hot to the touch. Although my mechanic did wonder if the thermostat was put in upside down, the one who replaced it told me he was very adamant in making sure it was put in the right way. After pulling the dipstick out, he stated that the oil was fine. I did not hear him say anything about the engine itself except that it was fine.

He asked a lot of questions and I could answer them to the most part. No visible white smoke coming from the exhaust pipe or out the engine. I have poor smell and wasn't able to tell him about any sweet odor when I drove it. He did not directly tell me whether or not he could smell it in any one particular spot with the hood up. The temperature gauge has only gone over the normal amount a few times this year. Each of those times revealed a lack of coolant in the tank and the radiator.

If this doesn't work, I am highly considering to continue running it and adding coolant when needed (there isn't much trade-in value). If it stops running, I will have to buy a new car.

Okay, this is very helpful. It sounds like this guy is asking the right questions, and looking in the right places. It sounds like some leaky gaskets and a bad water pump. However, I would encourage you to ask the mechanic to check the fan clutch. Basically, when you start the car, the fan will spin very strong for a short while, and then subside. It won't stop completely, but it will slow so it doesn't cause a lot of drag on the motor. Don't bother looking at it, listen for it. If you hear a ROAR when you give it gas on a COLD motor, then the fan clutch is gone. They're about 30 bucks and he's gonna have to take that part off when he does the water pump anyway. It won't take anything to move the blades over. In mine, the mechanism to redirect the fluid internally seized, causing it to be on constantly. It used to roar, and eventually it took the water pump with it. Although it's possible the water pump died of its own volition, check to make sure it's not caused by something else. 78k on a water pump is a smidge pre-mature...but not unheard of.
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The fan is extremely difficult to visually check, it will look fine, but it must be tested in operation. If unsure, just leave it alone, it can be replaced later if found to be faulty. I'm just telling you my experience when I lost a water pump, that it wasn't actually the pump that had gone bad. The fan is driven off the water pump it's connected directly to it. The fan isn't perfectly balanced, so excessive spinning and overuse of the fan (especially at high RPM's) will cause vibrations in the water pump and beat the bearings up. That's what happened to me, but I'm not saying it's a given that it happened to you. Like I said, when he puts it all together, have him test the fan clutch by my method described above. You'd hate to put a pump on, and then 10k down the road, have to do it all over again for a $30 part!

Yes, have him do the timing belt while he's in there. It's been a while since I did the repair, but he's right, the water pump sits behind a lot of the covers for the timing belt. I can't remember if I had to take mine off or not, but it's a good idea to do it while he's in there. He's got to remove most of the stuff anyways, it won't be much for a belt while he's in there. Good idea to replace tensioner too. He should be able to tell if the tensioner is shot or not. Many people, for good reason, will tell you to replace it. I replaced mine (again, only about 30-40 bucks). If you're SUPER tight on money, you can leave it alone, but there are times to be cheap and....well, you know the rest ;). If you want to save some money, head over to to buy the parts yourself. If he'll put them on, hold on to that mechanic! (many won't). 2 reasons why you should replace the timing belt. First: Coolant leaking on the timing belt can compromise it. Not sure if this happened in your case, but it's possible. I had a ford escort that this happened to that toasted the belt. Second: You're almost at 100k, when you should replace it anyway. Once you have a good timing belt and a good water pump, you don't have to think about it for another 100k miles. Good peace of mind. Remember, these engines are interference, which means if the timing belt pops, the pistons will hit the valves and all sorts of mayhem will ensue. You might be told at that point to "get a new car", which I know is a proposition you do not want to be faced with.
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