Regarding the latter, a Nissan from an out of town owner was towed in with a trashed rear differential. In the past I’ve seen probably half a dozen carburetor castings leaking fuel internally (mostly Ford), a Subaru extension housing on a manual transmission, and not one, but two, Nissan rear differential leaks. Porous castings are rare but do happen from time to time. I think there may be a Honda technical service bulletin out about porous engine castings on both the 4 and 6 cylinder engines. 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?įinally, 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? Would a compression test be any use at this point? But I would imagine the mechanic looked hard at the head when he had it off. 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. I hope it turns out to be that simple, but I don’t like it. 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. One potential explanation is contamination from a damaged transmission cooler in the radiator if it has one. Tomorrow we’ll put drops of each fluid on separate pieces of white paper towel to better see the color. The coolant in the overflow reservoir evidently leaves a black coating on the plastic surface of the bottle. The oil and the transmission fluid each seem ok based on dipstick observations, though that may not be a convincing way to judge. 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. That sounds bogus to me, but all these people reported the same thing - ie, NO head gasket problem. The explanation given in most of those cases was what evidently has a name: “porous engine block”. 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. But it has at least been drained and refilled, maybe “flushed”…I just don’t know yet. 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. 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. He suspected the head gasket, but when he pulled the head, he didn’t find any obvious explanation for the contaminated coolant. Her regular mechanic, a very good friend of hers, is a Honda dealership mechanic but does some of her repairs as a favor. My friend’s Honda had oil in the coolant. 1998 Honda Accord Coupe, 4 cyl ULEV V-TEC / SOHC.
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