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Three Mechanics, Three Opinions

Hi all,

Three mechanics have given us three different opinions about what is wrong with our 2003 Nissan Sentra. I’d like to hear from the Car Talk community.

The problem started when our car began to shake when we drove above 40 miles per hour. We got the radiator replaced. However, the car still would not always start.

We took it to the Nissan dealership. The mechanic there said it needed a new fuel pump.

We took it to mechanic #2 for a lower-cost fuel pump replacement. However, the car has started every time for them. So they cannot be confident that there is something wrong with the fuel pump. The fuel pressure does drop off after turning the key off. This mechanic said our main problem is that there is antifreeze in cylinders No. 2 and 3 of the engine (likely from when our radiator broke). There is either a crack in the cylinders or the head gasket has failed. They are estimating $1,200 to $1,600 to fix this. They said if we don’t take care of this, the antifreeze will continue to circulate and damage the engine further.

The Nissan dealership says if there were antifreeze in the engine, the check engine light would have come on. Also, they say they would have noticed if there were antifreeze in the cylinders. Their opinion is the fuel pump is only thing that needs to be fixed.

We then called mechanic #3 to get another opinion. This mechanic specializes in Hondas/Toyotas/Nissans. He hasn’t looked at the car yet, but he thinks that the motor could be damaged since the car was shaking when the radiator broke. He says he thinks it is unlikely that the fuel pump needs replacing, and he thinks the check engine light would not detect the antifreeze in the engine.

Fuel pump, antifreeze in cylinders, or motor? Or all three? What do you think?

The car has about 85,000 miles on it.

How fast does the fuel pressure drop off after the key is turned off?

And it’s true. If there were coolant in any of the cylinders it would cause a misfire in the engine and turn the Check Engine light on. Plus there would be steam coming out of the exhaust pipe as the coolant evaporated out of the cylinders.

Tester

I think I agree with fuel pump.

It may be possible that you’re getting antifreeze in the cylinders, but you would have bright white smoke from the exhaust. As it was said before, it would also cause a misfire and throw a code.

If you have enough antifreeze in the cylinders, that can also cause a no-start problem. When the car was failing to start, would it just turn over and over with no luck, or would it sputter and attempt to start?

Was the car allowed to overheat?

This is not making sense. You got the radiator replaced because the engine was shaking? Is there a paragraph or two missing there somewhere? After the radiator was replaced, the car still won’t start, another paragraph missing? The fuel pressure drops off and they found antifreeze in the cylinders, two or three paragraphs missing?

None of these things are related with the exception that if the fuel pressure is dropping off after turning off the key and the engine not always starting. That would indicate a leaking injector that is flooding the engine making it hard to start. It might also make it run rough but should set a code.

@keith it’s buried in there, when mentioning mechanic #3

“the car was shaking when the radiator broke”

A lot of story missing here; a lot.

It would be interesting to know if the dealer charged them a fee or not for any diagnosis. Having something diagnosed and then taking the car away to “get it done cheaper somewhere else” can be a real irritation to put it mildly.

It could well be that this car has multiple problems but determining if the engine is even worth saving should be the first step.
If the anti-freeze in the cylinders is true and based on the radiator comment it could be that it’s semi-fried at least.

if the fuel pressure drops quickly when the engine is shut off, that’s likely the check valve inside the fuel pump is faulty. this can cause a hard start/no start condition when hot as the fuel in the rail boils off. if there is coolant in the cylinders, it may not be bad enough to cause a misfire all the time. recommend a cylinder leak-down test for cooling system leakage, and you may need a pump, too. i wonder what else is wrong, is it still shaking?

It seems like the first thing you need to determine is whether or not coolant is in the cylinders. Besides reading the ECM codes, there are various tests shops can do that can determine whether there is any path between the coolant and the cylinders. One is called a “leak-down” test. Another tests the chemistry of the coolant itself for signs of exhaust gasses. And they might suggest a compression test. I wouldn’t expect any of these tests to be super-expensive. Maybe ask if one or more of these tests be done to confirm/disprove the coolant-in-cylinder theory.

Once you know that, one way or the other, then you’ll have the knowledge you need to procede.

Best of luck.

The problem started when our car began to shake when we drove above 40 miles per hour. We got the radiator replaced

I’m as confused as others have mentioned. Was the radiator replacement expected to correct the shaking above 40mph? That’s really a tough one to understand. Did the new radiator solve the shaking?

I would suspect the radiator leaked out most of the coolant causing an engine overheat and head gasket failure. The shaking was the misfire in the affected cylinders due to coolant in the cylinders.
Or, the engine overheated then blew the head gasket and the pressure created popped the radiator. Either way find out definitively if there is water/coolant in the cylinders.
Good luck

The story is very incomplete and very convoluted. But I’ll make try a sscenerio based on a few assumptions and you tell me if I’m close or way off.

If I understand correctly, you were driving along and the car started shaking. You kept driving. It was determined by a shop at that time that (1) the radiator had failed, likely causing the shaking as the engine overheated. The radiator was replaced (by the Nissan dealer?). The dealer also said you need a new fuel pump.

You took it to a second shop to save money on the fuel pump, and the shop was unable to confirm that the fuel pump was bad. He sugested that the shaking may have been from antifreeze that he found present in cylinders 2 and 3 of the engine. He suggested that the antifreeze got there because either the headgasket had failed or the cylinder had cracked. He said it would be expensive to correct.

So you called a third shop, gave him the scenerio, and he said the engine probably sustained damage when the raditor broke. He doubted that the fuel pump needs replacing.

These are not three different stories. Your radiator broke, the coolant ran out, the engine overheated until the headgasket blew, and between the blown headgasket and the coolant getting drawn into the cylinder the engine started shaking. So, as a minimum, your headgasket is blown. Worst case (and likely) you have internal damage to the engine due to ingestion of coolant. You might even have a warped head.

You’re in for a very expensive bill as a minimum…and if you’re lucky. The head will have to be removed. The headgasket will have to be changed, and the head milled if it’s warped. Even if all goes well at that stage, you’ve sustained internal damage thal’ll shorten the life of the engine.

Sorry, but I think the dealership just replaced the most obvious problem, the blown radiator, and misdiagnosed the shaking as a weak fuel pump. I think the other two shops are both telling you the same thing in different words.

Thank you for your feedback, all.

To answer the questions:

  1. The fuel pressure jumps up to 52 psi when turning on the key; then it drops to 8-10 psi in about 50 seconds after being shut off.

  2. When the car was failing to start, on the first attempt it would act like it would want to start. Then it would turn over and over again without starting.

  3. We were driving home when suddenly our car began shaking. We drove the rest of the way home (15 minutes) below 40 miles per hour so it would not shake. When we took the car to a mechanic, the mechanic said the car was shaking/overheating because the radiator had broken. The new radiator stopped the shaking.

The fuel pressure should drop slowly over a 10-15 minute period, not in 50 seconds. This indicates that the fuel pump check valve isn’t able to hold the residual fuel pressure. And this could be the reason for the hard starting.

The next time you go to start the car and you know it’s going to give you this problem, just turn the ignition switch to the on position so that the dash lights come on for two seconds and then turn the ignition switch off. Repeat this a half dozen times and then try starting the engine. If the engine starts right up the problem is with the check valve in the fuel pump assembly.

Tester

I agree with you about the check valve, but that won’t cause shaking except perhaps on initial startup. I still think based upon my understanding of the problem that the engine probably has a blown headgasket and a leakdown test is in order. And I stilll think that there’s actuallyy consistancy in what the verious shops are telling the OP.

Well a “broken” radiator causing a car to shake above 40 mph is a new one on me. I don’t see a connection, especially with no overheating.

I’m not so sure there was no overheating. I guess that accounts for our different perceptions of what might have happened. I suspect the post is incomplete. I suspect that there are details that have been left out, not intentionally but left out nonetheless. The only way I was able to make sense of the post was to assume overheating, even of the OP didn’t notice a warning light. .

@Tester the fuel pump check valve isn’t the only thing that could cause fuel pressure to drop off rapidly after shutting the engine off.

@db4690 You’re correct. There are other things that can cause the fuel pressure to drop off rapidly. These include a defective fuel pressure regulator and/or a leaking fuel injector. But usually when this happens the engine will have a strong gas odor and/or the engine will run rough when started with maybe a Check Engine light with a misfire code.

I’ve been wrenchin’ on cars for over 45 years. So there’s nothin’ new you can tell me.

Tester