Over the last decade, the engines that have been used in the Honda and Acura line of cars and SUVs not only deliver many miles of service, but their performance level sets a standard that few car makers in their class have been able to match. Additional proof of both the reliability and potential of these engines is the popularity they enjoy in the sport compact market. I think it’s safe to say that the popular B Series twin-cam Honda engine is the current-day small- block Chevy, enjoying great popularity among both tuners and vehicle owners in general.
That’s not to say there’s never been a problem, but they’ve certainly been few and far between. One such problem is head gasket failure on early ’90s Civics. Honda was quick to react to the problem and developed a gasket and hardware to remedy it. The TSB lists the updated gasket and head bolts that will prevent a recurring problem.
We won’t cover the nuts and bolts of head gasket replacement in this article, since your technical information system will walk you through those procedures. Instead, we’ll talk about head gasket failure symptoms and diagnostic strategies. It’s the slightest head gasket leaks that will present the biggest diagnostic challenges. In such cases, the customer usually will notice a symptom that results from lost coolant.
It may be an overheating issue but, many times, it’s a problem the customer doesn’t relate to low coolant. It might be a “no heat” or “the heat is coming and going” complaint, or the idle fluctuates as a result of the low coolant level not allowing good flow to the warm-up device. When you ask your customer if he/she has noticed a coolant leak, the answer will be “no.”
The more severe cases of head gasket failure will be easier for the customer to notice. It’s hard to miss the telltale white steam coming from the tailpipe in the morning and the accompanying odor of coolant burning. If they ignore it for just a couple of days, the overheating will bring them to your shop soon enough but, hopefully, not on a flatbed. There is always the threat of the engine hydrolocking as a result of the cylinder being filled with coolant, preventing it from cranking over. When faced with this situation, don’t continue trying to start the car. Pull the plugs, cover the holes with a shop towel and crank the engine. There’s no missing the coolant escaping the cylinder.
GETTING STARTED
With less obvious coolant loss (even though the customer noticed no leaks), our first step is to check for external leaks. Put the pressure tester on the car and check the usual suspects, like the radiator. Look at the bottom of the timing cover for evidence of a water pump leak, take a good look at the thermostat housing area and move the hoses around. Be patient; sometimes there will be only a slight leak, so give it time to surface.
While external head gasket leaks aren’t common on Hondas, they can occur and should be no problem to diagnose. Most will leave evidence and can be confirmed with the pressure test. But make sure that the leak isn’t originating elsewhere. You don’t want to replace a good head gasket if the leak is actually the thermostat housing disguising itself, with the coolant traveling down the head-to-the-block seam. Also be aware of the oil-to-coolant oil coolers used on some models. This “sandwich-plate” device mounted between the filter and the block has coolant running through it to maintain a stable oil temperature based on coolant temperature. As these vehicles get older, we’ve seen the effects of road salt and rust end up as pin holes in these units, easily mistaken for a coolant leak at the head gasket.
IN SEARCH OF INTERNAL LEAKS
If no external leak turns up, check for an internal one. There are a couple of ways to proceed ‹ two tests that are each performed with the engine running. One is a dye test where the air that’s at the top of radiator tank is drawn into a turkey baster-type device fitted with a check valve, and then passes through a dye that changes color if exhaust gases are present. This is a reliable test as long as the chemicals are fresh (the dye has a relatively short shelf life). A variation to this test is to use your exhaust analyzer to sniff the same air that the dye is analyzing.
When performing these tests, take caution to avoid coolant contamination. If contamination mistakenly happens with the dye, it will cost you some chemicals. But, needless to say, the consequences are much greater if you suck coolant into the exhaust analyzer.
The most accurate and our preferred test method is a cylinder leak-down test. This test involves bringing the cylinder to be tested to TDC and introducing compressed air into the cylinder, while observing the coolant level in the radiator. A leak-down tester lets you see how much the cylinder is leaking in percentage points. We use a dual gauge tester where you set the regulator for 100 psi going into the cylinder, while the second gauge will show what the cylinder will hold. This is very useful information to determine how well the valves and rings can control the cylinder pressure. Always make note of the readings as they give you great insight into the engine (more on this later).
But when testing for head gasket leakage, we’re more concerned with the reaction of the coolant in the radiator to the pressure. When the offending cylinder is pressurized, it’s hard to miss the reaction of the coolant. I’ll give what looks like good cylinders a couple of minutes just to be sure. If you find high leakage, it takes only a couple of minutes to determine what’s leaking. Using a stethoscope, listen for escaping air in the spark plug holes and dipstick tube, checking how well the valves and compression rings are sealing.
