1998 Honda Accord Coupe, 4 cyl ULEV V-TEC / SOHC. 170 k.
My friend’s Honda had oil in the coolant. Her regular mechanic, a very good friend of hers, is a Honda dealership mechanic but does some of her repairs as a favor. He suspected the head gasket, but when he pulled the head, he didn’t find any obvious explanation for the contaminated coolant. Now, with a new head gasket, the coolant seems to show the same problem, though there’s some speculation that what has reappeared may be residual contamination after having the cooling system drained and refilled. Or not. I don’t have details on how much effort was put into cleaning the cooling system, or how much effort it takes to get the system clear of oil if that’s even the problem. But it has at least been drained and refilled, maybe “flushed”…I just don’t know yet.
Some internet research that I didn’t conduct revealed a pattern - many reports of exactly the same problem, that is, 98 and 99 4 cylinder Honda Accords with oil in coolant and no problem with HG. The explanation given in most of those cases was what evidently has a name: “porous engine block”. That sounds bogus to me, but all these people reported the same thing - ie, NO head gasket problem. Is this porous engine really another way of saying cracked head, or cracked block? The mechanic has not yet examined the car after the head gasket replacement, and has not yet rendered an opinion.
The oil and the transmission fluid each seem ok based on dipstick observations, though that may not be a convincing way to judge. The coolant in the overflow reservoir evidently leaves a black coating on the plastic surface of the bottle. Tomorrow we’ll put drops of each fluid on separate pieces of white paper towel to better see the color. The car runs fine.
One potential explanation is contamination from a damaged transmission cooler in the radiator if it has one. But wouldn’t a breech there only result in coolant entering the transmission coolant line due to the pressure differential, or would it cross contaminate? And if they did cross contaminate, would the contaminated coolant look more red than black if it were transmission fluid in the coolant? Maybe not - what color do you get when you mix red trans fluid with green coolant? I’d guess an indistinct ugly brownish. I hope it turns out to be that simple, but I don’t like it.
So, back to oil…It seems to me that if the coolant is contaminated but the oil is not, then it must be combustion pressure exceeding the relatively lower pressure in the cooling system, driving oil toward the cooling system, making me think the problem is in the head. That would be relatively good news. But I would imagine the mechanic looked hard at the head when he had it off. Would a compression test be any use at this point?
So what’s the best next diagnostic step? Is there some reliable test to determine if it really is oil - not tranny fluid - in the coolant? Or does the color say it all? If it is oil, then what? Begin looking for a donor car with a sweet running engine?
Finally, I gotta ask: has anyone else ever heard of “porous engine block” problem in Hondas? Is it really possible that there’s a metallurgical problem with the casting of these engines?
Thanks for any advice on this one.