I've got a 1976 280Z with stock fuel injection. The FI was not on the car when I bought it, and I had a shop in Edmonton, Alberta restore the car to FI using parts from a donor car. They did an incomplete job.

Recently, I've been having trouble with the thermostat opening way too late. I noticed that the lines that run from the cooling water through the intake manifold (or a piece attached to it, just below the secondary air regulator), were not connected. I got a look at a 280ZX and saw how they were meant to be hooked up, and restored the connections to my 280Z. My thermostat now opens smoothly, but there's another problem. The car now seems to be burning antifreeze until warm. Lots of white smoke from the tailpipe until it's at temperature.

Is there any chance that the connections I restored are allowing cooling water into the intake? If not, just what does that cooling water loop do, anyway? Any temperature-based modifications to the FI system should be handled by the temp sensor and the thermotime switch, both located in the thermostat housing.

Any help would be appreciated. I plan on disconnecting the water from the EFI intake manifold and looping it back on itself to see if the problem persists. If it does, I've likely warped the head and caused a head gasket leak.

I didn't know that the intake coolant passages existed on the FI cars, but I guess it stands to reason that they would.

My guess is that a previous owner disconnected the coolant lines because there was a hairline crack in one of the passages that allowed antifreeze to seep into the intake manifold under pressure. Once the engine is up to temperature, either the pressure in that passage drops when the thermostat opens, or the crack closes when the manifold expands.

That is only a guess.

Is there any chance that the connections I restored are allowing cooling water into the intake? If not, just what does that cooling water loop do, anyway? Any temperature-based modifications to the FI system should be handled by the temp sensor and the thermotime switch, both located in the thermostat housing.

Any help would be appreciated. I plan on disconnecting the water from the EFI intake manifold and looping it back on itself to see if the problem persists. If it does, I've likely warped the head and caused a head gasket leak.

The intake manifold only has a mounting provision for the "cooling loop", there is NOT any orifice at that point which would allow coolant to seep in, it' my guess you overheated and warped the head.

The loop is only needed to warm the air regulator, it operates independently from the Thermotime switch. Its only function is for high idle warm up - without the "coolant loop" the car will high idle indefinitely in colder temps, speaking from experience on that one! For anyone in warmer climates, I would recommend removing it completely.

Edited July 8, 200915 yr by preith
grammar

@ Philip:

Thanks for your help. Not the news I was hoping for, but not a big surprise, either. I live in central Alberta, so while you couldn't really consider it a "warmer" climate (not by a long shot!), the car only gets driven in the summer months, and so the loop under the air regulator is likely unnecessary.

As for the the head gasket leak... Well, with 95,000 miles on the engine, I may as well get the whole thing rebuilt. I mean, if I just replace the gasket, it might not do the trick, but if I'm going to have the head shaved, I may as well do the valves. Do the valves, and the oil control rings will probably start passing from the increased compression... and it just snowballs from there. Probably cheaper to pull the whole engine and have it done in a one-shot deal.

Ken

Assuming that the engine was otherwise cared for approptiately, I doubt there's enough wear on the rings to warrant changing them out at only 95,000 mi considering that these things will easily do 300,000. On most well cared for L6 engines you can still see the hone marks on the cylinder walls at 90,000. Depending on whether and how much the head needs to be milled, it may not be necessary to shim the cam towers and rebuild the whole head. My recommendation would be to take it to someone who knows Z engines and get a qualified opinion before throwing lots of $$$$$ at it.

Edited July 9, 200915 yr by =Enigma=

Assuming that the engine was otherwise cared for approptiately, I doubt there's enough wear on the rings to warrant changing them out at only 95,000 mi considering that these things will easily do 300,000. On most well cared for L6 engines you can still see the hone marks on the cylinder walls at 90,000. Depending on whether and how much the head needs to be milled, it may not be necessary to shim the cam towers and rebuild the whole head. My recommendation would be to take it to someone who knows Z engines and get a qualified opinion before throwing lots of $$$$$ at it.

Good points, you should probably hold off on diving in with the checkbook just a bit. A good starting point for diagnosing any head gasket problems would be a leak down tester, done both at cold temps and after warm up. Also, if it's truly leaking antifreeze into the exhaust it will give a very distinct smell otherwise the smoke could be something else.

I live in central Alberta, so while you couldn't really consider it a "warmer" climate (not by a long shot!)

Yes, I don't envy you, the climate here in Wisconsin is bad enough! On a side note, I'm pleased to see the IRL kept the Edmonton race on their scheduled this year, in just a few weeks too.

I only recently purchased the car from a guy in Florida. I really couldn't say how well he did or did not take care of the engine. The valve seals do let a little oil out at startup, so the head needed to be done anyway. Did the valve lash not too long ago, and the cam and valve train all looked/felt good.

I was going to have the engine rebuilt at some point anyhow. The only difference it will make is in the order in which things on the car get done. Engine this year = suspension next year, and bodywork the year after that.

Since we're in the EFI forum, let me ask this... can I remove the EGR valve and blank it off on the intake? I've got a header on the car right now and no provision for EGR from it. It would be nice to clean up the look of the intake side of the engine, and probably reduce the possibility of vacuum leaks in the future, too.

I've had the EGR, and all the tubing, off for a few years. It wasn't working anyway. If I ever get the engine out, I would cut off the egr lobe and close it up.

Edited July 9, 200915 yr by TomoHawk

I've had the EGR, and all the tubing, off for a few years. It wasn't working anyway. If I ever get the engine out, I would cut off the egr lobe and close it up.

A popular swap is the earlier non-EGR N42 manifold, found on the 75-76 years.