Archive for the ‘Auto Repair / Engineering’ Category

1990 Honda Accord radiator fan is not running, overheating in traffic

Sunday, July 16th, 2017

This summer has been a hot one and I noticed that my 1990 Honda Accord began to overheat while crawling along in traffic. A quick triage revealed that the radiator fan was no longer running at all. In the end, the fix was to bypass a broken wire in the main wiring harness. More details below.

Notes on timing belt maintenance for 1990 Honda Accord

Tuesday, April 28th, 2015

This job can be a little harder than it needs to be, especially if you are missing parts of your brain like me. Here is a list of things to watch out for.

Rear Struts On 1990 Honda Accord: Not So Fast

Monday, April 27th, 2015

One bolt and two nuts per side are all that’s between you and a smoother ride. How complicated of a job could it be? A little too complicated, it turns out, at least if your car has ever lived in an area subject to underbody rust. A seized bolt in the lower bushing can ruin your Saturday. Here are the steps to successfully complete this job.

Repair Honda Accord code 41 – O2 sensor heater circuit

Wednesday, March 10th, 2010

I recently fixed a persistent problem with my 90 Honda Accord EX with a F22A4 motor, that the oxygen sensor heater circuit was malfunctioning and throwing a “check engine” code #41, causing poor fuel economy. Here is how to troubleshoot this problem.

How to replace the front to rear brake line on a 91 Ford Explorer

Sunday, January 24th, 2010

I have a 91 4-door Explorer with 4 wheel drive and rear anti-lock brakes (RABS). While bleeding air from the brakes to try to solve a spongy pedal, the brake line that goes from the proportioning valve to the RABS pump “popped” and brake fluid began to drain onto the concrete.

Why does this brake line fail prematurely? Ford wrapped a spring around it for some reason, probably to dampen vibration, but the spring is an incompatible metal which corrodes the brake line in accelerated fashion. The result is total loss of rear brakes, a soft pedal, and a brake fluid leak.

Here is what to do about that problem. We will replace the broken brake line with Poly-Armour lines which are corrosion resistant, easy to bend, and which simply screw together with no flaring tool necessary.


What they didn’t teach you in brake bleeding school

Wednesday, June 20th, 2007

There are always unforeseen problems when working on cars. Bleeding the brakes is no exception.

There are lots of different ways to bleed the brakes. I use a hand vacuum bleeder. It can be purchased for less than $30 and makes brake bleeding a one man job. Another very cheap tool is Speed Bleeder one-way valves.

Have a glass jar nearby to collect old brake fluid. When using a vacuum pump, put the vacuum tip into the jar before removing the collector from the vacuum pump to avoid spillage.

Always keep the master cylinder topped off. Occasionally take a break by closing the bleeder valve and go check on the master cylinder.

Bleeder valve is Frozen

Yes, you are doing the right thing. You are trying to loosen the piece that has a nipple on one end and that threads into the brake cylinder on the other end. It will be above the brake line fitting. Just make sure you are trying to turn the valve the right way. Lefty loosey, but it’s reversed if you’re coming from the other side. Use the box end of a wrench to loosen the valve. If the valve has not been opened in a long time, don’t risk breaking it — spray PB Blaster or Kroil or similar catalyst penetrating oil onto the screw and let it soak in for a day or two. If you break the valve off, your job just got a lot more painful. The valve only needs to break loose and move at most 1/4 turn for you to do the job. When you reinstall a valve, put some axle grease on the exposed threads to help protect it from future corrosion.

Air Rises

This should be obvious, but sometimes the obvious escapes us. The vacuum pump and collector must be held in the air ABOVE the bleed fitting in order to accomplish the bleeding. Also, if there are any high spots in the system, the end of the car being bled must be elevated (elevating might be a good idea in general — it certainly doesn’t hurt).

When using a vacuum pump, pump it to about 20 mm Hg and pump some more whenever it goes below 15 mm Hg.
First, you want to get old brake fluid out and discard it. Old fluid will be dark with moisture and contamination, new fluid will be clear and beige-colored. Secondly, you want to purge the air from the system. You should see lots of bubbles at first, eventually trailing off and running clear.

Nothing happens

You might have to tap the brake pedal to push a clog out of the bleeder nipple, especially if it was missing the rubber cap.

The bubbles won’t stop

You’ve been bleeding for a while. The bubbles seem pretty consistent, not trailing off, or there is a distinct foam to the pumped fluid. You might even hear a hissing noise. The problem here is not anything you’re doing. It is air passing the threads on the bleeder and being pulled in with the brake fluid. This would not be a problem except it makes it impossible to tell when you have actually bled the system. To fix this, you must take the bleeder valve out all the way (I used a 5/16 socket to make this easier) and wrap teflon pipe thread tape around the threads several times. Reinstall the bleeder valve and try again. Like magic… hopefully. If it still seems to be leaking air, you may simply have too much corrosion on the bleeder valve for it to correctly seal. Go and buy a new bleeder valve, wrap it with teflon tape, and you should have no more bubbles.

Hopefully this is all the information you need to get the air out of your brakes. When you’re done, top off the master cylinder, reinstall the cap, and remember to pump your brakes to build up pressure while the car is still parked. (If you did not also install a new master cylinder, don’t allow the pedal to hit the floor though, or your master cylinder is likely to be damaged.)

Oil consumption, rich mixtures, etc

Thursday, March 1st, 2007

You may know that a lean mixture causes reduced power, preignition, and detonation (the latter two especially in the presence of excessive heat). It also causes increased combustion temperature which consumes oil.

You may also know that coolant in the exhaust from an internal engine leak will destroy your O2 sensor and catalytic converter.

It is common belief that the only problem a rich mixture causes is reduced gas mileage and increased pollution. So when a car starts to get bad mileage and a rich smelling exhaust, it is usually ignored.

What you may not know is that a rich mixture causes several problems as well.

  • A rich mixture will send more unburned HC into the catalytic converter to be burned, which overheats and destroys the converter over time.
  • A rich mixture will foul spark plugs, reducing mileage even more and exaggerating the effect on the converter as more unburned fuel enters it.
  • A rich mixture causes carbon build-up in the cylinder, reducing the life of the piston rings and possibly causing them to stick.
  • While a rich mixture does lower combustion temperature, a rich mixture will wash oil from the cylinder walls, reducing lubrication and causing the oil that is washed off to be consumed.

Some things that can cause a rich mixture:

  • Bad fuel injectors (spraying a stream instead of a fog)
  • Bad O2 sensor (reading lean all the time, so ECM richens mixture unnecessarily)
  • Bad ECM, or running in open loop due to failure of some sensor needed for correct closed loop operation
  • Insufficient coolant (ECM does not go into closed loop)

Advanced timing also causes higher ignition temperatures and therefore greater oil consumption (in addition to detonation and a ruined engine if a knock sensor is not present).

This is also a good reason NOT to “warm up” a modern fuel-injected engine with a modern motor oil in it by idling it. Doing so simply prolongs the period when the engine is cold and running rich, and as such leads to oil consumption and contamination.

So if your engine is using oil and it’s not leaking externally, check the PCV valve, ignition timing, and rule out a rich mixture caused by bad fuel injectors, sensors or a clogged air filter, before tearing into the motor.

One way to check the mixture if no ECM code is present is to install a new O2 sensor and monitor its voltage after it is warmed up. The voltage should be around 0.7 volts. If you remove a vacuum hose, the voltage should dip to 0.3 volts or so. The injectors can be removed and serviced for $100-150 by mail order.

Oil Consumption and Bearings

It’s a well known fact that worn bearings lead to low oil pressure, wearing the rings which then allow oil consumption and allow more contamination into the crankcase, destroying the engine in a vicious cycle. Excessive bearing clearance is also partially responsible for that oil consumption. Worn bearings throw more oil up into the cylinder than the oil ring can dispense with, and the rest of the oil is burned. Then you have not only low oil pressure, but also dirty oil AND a low oil level to deal with.

So if you have a rod knock you’ve been ignoring, time to drop the oil pan and fix it right — before the bearing spins and repair of the engine becomes more difficult (requiring removal and cleaning of the engine, machining of the crank, and replacement of all bearings), the rod is thrown and repair of the engine becomes impossible, or the oil consumption and low oil pressure ruins the rings – replacing rings is an inexact science and best avoided when possible. Buy the correct size bearings (according to the stamps on the old bearings) and new rod bolts, then install the new bearings by cleaning the crankshaft, “clipping” the bearing into the interference fit grooves on the rod, applying oil, loctite, assembly lube, or nothing at all to the bolt threads as called for in the factory repair manual, and tightening the rod bolts to the correct final torque.

Sticking Rings

When people talk about “sticking rings” or “stuck rings”, be careful not to left the terminology confuse you. Stuck rings can actually refer to two events. The first is when an engine has been stored for a long time, and rust has set into the cylinders. The rings are “sticking” to the cylinder walls in this case, and the engine is seized. The best way to get this kind of engine loose is to soak with WD-40 or a penetrating oil, and attempt to turn the crankshaft by hand. When the rings come loose, they may or may not sustain damage, the only way to tell is to do a compression check. To prevent this kind of sticking rings, remove the spark plugs and spray WD-40 into the cylinders before storing.

The more common kind of stuck rings that happens in a motor that has been used even recently is that the rings themselves become stuck in the piston groove. The rings no longer seal against the cylinder wall because their “spring” is not allowed to expand against the cylinder wall. This happens when hard carbon and varnish build up on the rings. Once it has happened, there are several ways to address it. First, rule out all other sources of oil leaks, or oil burning in the head such as valve stem seals, worn valve guides, spark plug tube seals/o-rings, etc.

If the rate of oil consumption is relatively slow, try an ester motor cleaner like Auto RX. This is put into your oil and left in it for 1500 miles, then the oil is changed. It is a slow cleaner and may take two applications to demonstrate a difference.

If Auto RX did not help, or the rate of oil consumption is so fast that using Auto RX at $20 a bottle is uneconomical, then it is time for more drastic measures to get the rings unstuck. The motor cleaner used can be Marvel Mystery Oil, Seafoam, or even Automatic transmission fluid. Don’t use motor flush solvent (Kerosene) or fuel injector cleaner in the following procedures.

  • Remove spark plugs and add a small amount (teaspoons) of MMO, Seafoam, ATF, or Berryman B-12 to the cylinders. It is important that the engine is warm when you do this. Allow to sit for 30 minutes to two days. Crank the motor to spit cleaner out of cylinders, soaking it up with rags, then install spark plugs, allow the smoking to stop, and change the oil and filter. Repeat as necessary.
  • Alternately, the cleaner can be introduced through the brake booster vacuum hose with the engine warmed up, adding just enough through the hose for the engine to die. Wait 30 minutes, then start the engine, run it until the carbon burns off, and change the oil.
  • Change your oil every 1000 miles with 15W-40 diesel oil until the problem is solved. Before each oil change, add 1 qt MMO or ATF to oil, being careful not to overfill crankcase. Drive no more than 100 miles, allowing the motor to warm up completely for as long as possible. Change the oil and filter immediately. You can use a higher cleaner to oil ratio, but go easy on the engine if you do this. The oil in MMO is 3W and ATF is 7W, which does not provide much protection to the engine bearings, and if the filter is clogged, any suddenly loosened particles could clog the oil pickup.
  • Before each oil change, add several quarts of MMO, ATF, or Seafoam to a tank of fuel. Change oil when it becomes dark.

You can combine any of the above strategies, i.e. if you want to add MMO to the crankcase and Seafoam to the intake before changing oil, that is a good idea.

In order of solvent concentration (and reverse order of oil protection): Motor flush, Seafoam, MMO, ATF. When using in a 75% oil/25% cleaner concentration in the crankcase, you want to be very careful not to load the engine when using flush, be “nice” to the engine when using Seafoam, and you can drive the engine as normal when using MMO or ATF. Some people fill and run the entire engine with MMO/ATF immediately before an oil change, do not under any circumstances rev or load the engine if you do this.
If you choose to use a kerosene motor flush product, it is important that you not allow the engine RPM to increase above idle or place a load on the engine, due to the risk of running the bearings dry. Solvents such as those contained in MMO, top end cleaners, and motor flush will cut through the oil film on bearings, so any oil starvation will then lead to a bearing failure.

To prevent rings from sticking in the future, use a good detergent motor oil such as Mobil 1, or even 15W-40 diesel oil — since it has more detergents to prevent coking in diesel engines — obey the oil and filter change intervals, fix any other sources of oil burning (such as worn valve stem seals and excessive rod bearing clearance) as soon as possible, and don’t allow your motor to run rich. Many motor oils claim that their detergent packages will gradually unstick rings, but if this is true at all, it is a much slower process than the above techniques.

Fender rust on 1990-1993 Honda Accord

Sunday, February 25th, 2007

You may have noticed that most 1990-1993 Honda Accords have significant rust in the rear fenders above the rear tires while the rest of the body is rust free. There are a few causes.

The first cause is road salt and grime being kicked up in between the rubber splash guard and the lip of the fender. Car washes do not get to this salt and grime, and so it begins corroding the fender on the inside. By the time you see the corrosion, the fender has started to significantly rot.

The second cause is the drain hoses from the roof that are behind the upholstery panel in the trunk being clogged and allowing water to collect behind the fender.

If you have immaculate fenders, prevent this problem from occurring by REMOVING the rubber in the rear wheel wells so that there is nowhere for salt and grime to accumulate in a “hidden” place. Also, make sure the drain hoses flow freely.

The root cause is the fact that Honda (cheaply) failed to paint both sides and the underneath of the render, even though it was obvious from the design that the fender would corrode from both sides and underneath. There is nothing that can be done about it now besides to prevent the corrosion from starting. Once it has started, it is extremely difficult to repair. Once a rust hole begins at the fender, water will then leak into the trunk and corrode the inside even more!

Cooling fan runs after motor is shut off

This is perfectly normal. Spooked me though!

Oil pressure versus oil level

Thursday, January 25th, 2007

Why do many people report a lower oil pressure reading when their crankcase oil level is low?

We have to ignore the possibility of the pump displacing anything but oil in order to have a sound theoretical discussion. But it is possible that there is a large proportion of air trapped in the oil from frothing as it returns to the pan, or that the pickup tube — or its seal to the pump or block — has a pinhole in it that is covered when the oil level is higher (this should produce a relatively sudden change in pressure as the pinhole is uncovered, as opposed to a gradual change).

We also have to assume that the pump is not allowing oil to drain back out. But this is known to be false; an oil pump turned slowly enough will pump nothing but air. So there is not a linear correlation between pump speed and the volume of fluid pumped, because the faster the pump turns, the smaller the time period in each rotation where drainback could occur. The drainback effect will be more severe when the oil that wants to drain back is far above the level of the oil in the pan. So it would be expected that a worn oil pump allowing more drainback will produce lower output pressure when the level of the pan is low.

If we can assume that we are only pumping oil (a non-compressible liquid) and that a fixed volume of oil is pumped per rotation, assuring us that the same volume of oil is pumped through the engine no matter what the oil level is, then we must attribute a change in the oil pressure reading to lower oil viscosity.

What can lower oil viscosity?

  • compositional breakdown.

Compositional breakdown occurs as the oil is contaminated with moisture and hydrocarbons from blow-by, and as the oil polymers themselves break down from heat and shear.

The same amount of blow-by per firing cycle on a hot motor enters the crankcase regardless of the oil level, and the motor relies on being run hot in order to evaporate the moisture (but not the hydrocarbon contamination) from the crankcase. The oil is thus broken down and contaminated by time spent normally driving, and the effect of this contamination is worse when the engine spends a greater proportion of its total operating time warming up from cold. When the oil level is low, a smaller volume of oil must bear the same amount of contamination and thermal/shear stress that causes its breakdown.

It is expected then that a low level of used oil will produce lower oil pressure than a low level of new oil. It is also expected that the effect on oil pressure of being low a certain amount of oil will be more pronounced on engines with a smaller crankcase capacity. But it is also expected then that on any engine, being low on oil will not produce an effect on oil pressure if the oil in the crankcase is new (not contaminated or broken down in any way).

  • Temperature.

Oil viscosity is reduced when its temperature is raised. Circulated oil accumulates heat as it is sprayed on the cylinder walls, but radiates it through the oil cooler and oil pan, until an overall thermal equilibrium is reached. It is important to note that if a particular volume of oil was constantly recirculated, it would reach equilibrium at the temperature of the engine, while if it was seldom recirculated, it would reach equilibrium at the external temperature of the oil pan. Thus, the temperature of the oil has a high negative correlation with the time that the oil spends sitting in the oil pan.

The average time that a just-circulated volume of oil spends in the oil pan is determined by the amount of other oil that is in the pan below it. The other oil is cooler than the oil that has just circulated, so the just-circulated oil radiates its heat through the other oil and through the pan while it waits to be recirculated.

So, it appears safe to state that a low oil level is a causal factor in the increased temperature of the oil, and thus lower overall viscosity and lower oil pressure. This effect, unlike the effect of contamination and breakdown, should be present even if the crankcase is filled with new oil. Again, it should be predictable that the effect will be more pronounced in a smaller crankcase for a given volume of missing oil. But, while it is a causal factor, how much of a factor is it really? After all, the cold pressure and warm pressure in a full crankcase hardly varies enough to register on the needle. It seems like the temperature variance just doesn’t cause that big of a hit on the oil pressure.

Revisiting the air trapped in the oil, we would expect the same proportion of air trapped in the oil if the oil level is low, because the same surface area where air could potentially escape exists no matter what the oil level is. (Of course, if the oil level is far too high, a disproportionate amount of air will be trapped, but that is due to the crankshaft frothing the oil and not due to normal oil circulation.)

So if an engine is filled with a too-low level of new oil, we should expect a lower than normal oil pressure reading at all times due to:

  • Small leaks in the oil pickup that would be masked by a higher oil level
  • An amount of drainback relative to how worn the oil pump is

We should expect a lower than normal oil pressure reading at operating temperature — but possibly a vanishingly small difference — due to:

  • Temperature modification of the oil viscosity

We should expect a lower than normal oil pressure reading after a fixed number of miles of usual driving due to:

  • Accelerated contamination of the total volume of oil (occurring at a rate proportional to the percentage of time that the engine spends running below operating temperature)
  • Accelerated rate of polymer chain breakdown from shear and thermal stress. Thermal stress may not be a major issue. Since a low oil level causes an increased equilibrium oil temperature when the engine is running at operating temperature, we can also predict that the thermal breakdown of the total volume of oil when running at operating temperature will occur at a faster rate when the oil level is low. But as reasoned above, the equilibrium temperature probably will not rise enough to significantly affect the oil viscosity, so the effects of any increased thermal stress on the long-term viscosity of the oil may be negligible.

Chevy Cavalier 97 oil light flickering

Monday, January 15th, 2007

This might be the worst of the worst fears. You change your oil before a long road trip. You get off the highway and tooling around the neighborhood, there goes your oil light when idling at a stop sign. Kill the car and restart it, and all seems well for a few minutes and there it is again. Get out, check the oil which is full, and wonder what the heck is going on. Assume the new oil filter must have been bad and change the filter, only to end up with the same intermittent oil light. Well, I shouldn’t say intermittent, because it happens at low RPM and at high engine temperature, the same preconditions that would give you low oil pressure if you had a weak oil pump or excessive bearing clearance.

Well before you start fearing the worst, if you are sure the oil level is fine, the oil is not contaminated and that there can be nothing wrong with the filter, the next place to look is the oil pressure switch that sends the signal to the oil light. The way the switch works is that oil pushes on it until it turns off. Sufficient push on the “inside” of the switch from high oil pressure will turn off the light, while insufficient push from low oil pressure will allow it to remain on. Well, if the pressure switch is dripping oil from the plug side, that is your first sign something is wrong with it. The diaphragm internal to the switch is supposed to keep the oil on the engine side. If the oil gets through onto the electrical side, it will foul the connectors and give an intermittent connection. Coincidentally, the conditions for the oil getting through the diaphragm into the plug are the same as those that would give you an oil light on a tired engine: fresh oil and a hot engine at idle. Also, when the diaphragm begins to leak, that means that some of the pressure on the engine side is escaping through the diaphragm instead of pushing on it, meaning that the oil pressure will be sensed consistently lower than its actual value, and so the oil light will come on at times when the real pressure is actually fine.

The fix is to replace the switch. It costs 12 bucks at a parts store. You need a 1 1/16 inch deep socket to remove the old sender and install the new one. If the new sender did not come with teflon or similar sealer on the threads, use appropriate plumbing thread sealer before installing. Also, clean out the electrical plug with solvent and blow clear with compressed air to clear any oil from it that might foul the connection.