Hi All,

I am new here but have worked on various engines since I was a teenager in the 80s. Most engine problems are usually resolved with good basic troubleshooting and a reliable service manual, but I've come across a mystery that I am hoping might sound familiar to someone else:

I recently purchased a 1988 Nissan Pulsar that looked like it had been sitting for years & wouldn't start. It had only 94K miles and was all original. I traced the starting problem to a bad ignition control module, replaced it, and the car ran around town great for a few days. When I tried the freeway, however, I felt a gradual loss of power, some sputtering and then nothing. White smoke and the smell of coolant filled the engine compartment, so I assumed head gasket and had it towed to my garage.

Drained the oil to find no signs of water or other contaminants. Checked compression and found it was low - only about 90 PSI on the best cylinder. Then the strange thing - looked inside the throttle body and found an oily layer of coolant and fuel inside. I removed the head to find a nice looking head gasket with no signs of failure, and the same with the intake manifold gasket. Checked everywhere for cracks, leaks or any sign that would allow water to get up that far, but found nothing.

Inspecting the head I noticed that four of the eight intake valves and ports are heavily caked with black sludge, and that the intake butterfly valves are all equally nasty. However, the other four look clean. I did not perform a leakdown test since I was sure I'd find either the IM or head gasket blown, but now I'm stumped. Does any of this sound familiar to anyone?

Thanks in advance for any help & for having this great forum for guys like me. I can answer any questions you may have to help solve this most mysterious issue...

If I remember correctly, there is a water jacket that runs around the throttle body. Have you inspected the TB for any cracks?

Yes, since my original post I have dismantled the head down to the casting in search of anything that may have allowed coolant to get into the intake. There are no signs of cracks anywhere. I even pressurized the coolant passage you mentioned at the throttle body to see if any air leaked through, but that was solid too. I noticed that the intake manifold gasket was very tough to scrape away (brittle and adhered to the flange) except for one place between the first intake port and the coolant passage, so I am going with the assumption that perhaps with enough pressure, the fluid passed by at this point.

There was so much carbon and gunk on the valves that it's possible they were not closing properly - hence the poor compression results before tear-down. I spent several hours just going over everything with some solvent and a brush - now all is sparkling clean. I hope that once my gasket kit arrives and I put it all back together everything will be fine. I'm also considering bypassing that coolant line to the throttle body anyway since there's really no need for it here in sunny CA.

Thanks for the reply - I'll post with an update once it's all reassembled & (hopefully) running.

I'd be nice to have some pictures of your rebuild... it's getting more and more rare to see any pre-1990 Nissans on here.

Good luck!

Heath

Actually I will probably post some pics as this is becoming almost a full rebuild anyway and I'm becoming engrossed in the details. Maybe I should start a new thread.

Once the head was off I couldn't justify leaving the pistons in without taking a look. They were all slightly scored near the top edges and #1's top compression ring was fused to the groove. The thermostat didn't even flinch in boiling water so whoever drove this car before me probably overheated it. At least the cylinders were okay with just the normal glazing which I can easily hone. My theory now is that the temp sender was not accurate, the engine overheated and the steaming coolant condensed in the throttle body (the pressure and gas state of the boiling liquid probably made it past that weak spot in the intake gasket). I'm taking the head to be machined this weekend - might as well have the valves done too. Yes, much more than I had planned on but I can't do it any other way and still sleep at night. Oh well, at least I'll have the peace of mind that it's been done right when she's back on the road.