New World Datsuns...

Shrug. Forum Tourette's. I forgot what we were even talking about.

Rofl

It had occurred to me. Best case I have a bunch of miasdjusted cam followers. Although I'm not sure that follows either. I'll find out once I get the valve cover off.

Ok, I know what the problem is. It's no longer a problem. It's reeeaaaallllyyyyy stupid. The kind of stupid you get after working way too long on a project and having lots of issues. Causes you to overlook something simple. Here's what we know:

#2 and #4 cylinders were having the issue. No change in engine running when pulling injector connectors while running on those two.

Spark plugs good.
Spark plug wires good.
Fuel injectors good.
Fuel supply and pressure good.
Engine compression good.
Removed valve cover, valves good.
Valve springs and rocker followers good.
Camshaft good.

Who wants to guess the fine dumbassery of the hour?

2 and 4 injector connectors were backwards/in the wrong places.

Batch fire, wouldn't matter. Nope.

#2 & #4 plug wires swapped?

Haha, there we go. Swapped at the distributor cap. Of all the silly ass things. Good news is I've thoroughly checked all the systems now and I have nothing to worry about. Valve cover was so clean inside you could eat off it. I think having a 7.4:1 compression ratio was thwarting me too. Still ran without much problem. If I had swapped the wires on a 9.5:1 motor, it would have been a bigger issue.

Being driven crazy about something has its own issues, assumptions are made, I did that(spark plug wires), it is done move on, this is especially true when making big changes, I think I have done that a 100 times, there is no way I got that wrong, but while your doing that you are thinking about what is ahead more than what you are doing because you have done it a 100 times.
Everyone screws up, some like me more than others, that is why I liked making kingcabs, if it didn't work out, cut it out and do it over again, in the end no one will even be able to tell I screwed up, I cannot deal with electrical stuff because it is invisible and i cannot tell what the issue is, it just don't run right, anything I would do is just guessing, and replacing everything can be expensive, and the issue may just be a wire not making a good connection, if I understood the electrical part I would have a VG30E in my work truck.

Fact is I screwed up the 521 kingcab top big time but I didn't want to cut it out, so I put another top on top of the screwed up top, this likely was a good thing as it is double layered and even though it has a pretty thick layer of bondo on it it doesn't flex so nothing has cracked all these years later.

Yep, it runs much smoother now. Tried to overheat it, luckily only got to 218 before I realized I didn't have the fan on. Got things semi dialed-in, it's good at idle and quick romps of the throttle. Unfortunately, any sustained rpm holding is super lean at 19:1. So I'm thinking tomorrow I'll put it on the next fuel range setting up. It's on 6 now of 8 I think, so looks like I'm going to 7. I think it's going to need the long range time just due to the compression. Seems like too much, but even with the screws turned all the way up, it still runs way too lean at steady throttle. That's just in the driveway. Haven't taken it on the road yet. Want to get a closer baseline before I do that. And I'd prefer it rich to lean for safety.

So I paid for dyno tuning today. Well worth it. I'll just leave these here, talk amongst yourselves. Still a few things to do, and I probably have a head gasket issue just slightly which I'll need to take care of. Not a big deal though. I'll get more into that later, making dinner.

So the issue I'm dealing with is a sudden spike in the temperature. Runs at 190 perfectly, but then all of a sudden, spikes to 220-230, etc. Usually during hard acceleration in 3rd. Shift up, keep going, and it goes right back down to 190. Did it before, doing it now. Head gasket is about the only thing that makes sense. Not leaking or ingesting water, but just has some hitch and the right cylinder pressures annoy it and superheats the coolant. I'd like to think the gauge is wrong, but I ran the temp sender where there isn't any interference or heat sources. The water line it used to follow I removed anyway. The little manifold heat tube that keeps all the original IAC stuff happy.

The only other thought I had is if somehow the thermostat is contacting the temp probe, but during one of these spikes on the dyno (at cruise, not lean at all) the rad also spot temped 230 degrees. Pretty sure I need to replace the head gasket. And while I'm at it, install head studs so if I do turn up the boost I won't have to worry about it. Good news is it runs fine. And really it's not the worst to do a head gasket, though I wish now I would have taken it off when I refreshed the engine originally.

OK, this is my opinion and i had a similar issue in the past when I built my first LZ23.
I wanted to clean up the engine bay a little, so I removed the bypass in the thermostat housing, when I drove down the freeway the coolant temp was all over the place, it would run cool and then all of a sudden climb to almost in the red on the gauge and then back down to cool, around town it seemed fine, but steady 50+mph speeds it was unpredictable, then one day it over heated and blew coolant out the over flow hose, a couple weeks later I lost the head gasket.
I had never had this issue before so i looked at the engine and the only thing I had changed was that bypass, I put the bypass back in when I changed out the head gasket and never had an issue again.
I believe what happens is since the thermostat is outside of the head in its own housing, the coolant inside the head has to get supper hot to get the thermostat outside of the head to open, it actually boils inside the head, my issue was I let it get hot too many times(I really didn't pay a lot of attention to the gauge around town) and I had lost so much fluid that it over heated as I didn't have a radiator over flow container at that time.
If you don't use a bypass, or don't want a bypass all for one reason or another all you really have to do is drill an eighth inch hole in the thermostat as a bypass and all will be fine as it lets the cooler coolant out of the thermostat housing so the hotter head coolant can get to the thermostat to open it.
Here are 2 thermostats side by side, one with a hole for a bypass.


I went back until I found a photo of your engine and it appears you removed the bypass hose and replaced it with a sensor of some type, this is why I came to this conclusion I described above.

Oh now that's an interesting thought Wayno! So I can't remember if the thermostat housing on the motor now is the original one or not. I'll have to look at the pictures when I pulled it. The only stick in the works here is the radiator being at over temp when the gauge indicated it was. But I will definitely look into that. Because even when that happened, the engine still ran fine.

The jiggle valve on the thermostat I'm familiar with, I'm pretty sure mine has one. The bypass you're talking about, is it the one that comes out laterally from the side of the thermostat housing? That was a water nipple that went to the thermal valves for the air bleed system on the intake. It looped back around and connected to the small pipe that goes down around the head and tees into the thermostat housing. I have removed that, but it wouldn't cause any issues. That bypass was on the engine originally when I was running it with the original system. Still had the same problem. And really, though 3 years have passed, it may as well be the same time to the engine since it hasn't been run much at all until now.

The radiator would be super hot if the thermostat finally opened and all that hot coolant started flowing.
I noticed when driving down the freeway that the coolant temp would slowly start rising until it was almost in the red(HOT)and then it would drop most the way to "C" on the gauge, then it would start over again rising slowly till almost in the red again, over time my coolant level got lower and lower till that day it overheated, I filled it up but a week or two later it blew the head gasket.
Like I said it was my opinion, it's not that hard to remove the thermostat cover and drill a hole in the thermostat and put it back together to see if that is the issue, that's a lot easier than changing out a head gasket that may not be bad.

Yeah, the fact that it happens so suddenly is the real thing that worries me. I'll definitely check the thermostat housing anyway. Going to have to remove it for yanking the head off anyway. What I'm thinking is possibly the head is lifting due to old bolts. Usually it wouldn't happen except if I'd upped the boost, but being they're old and so is the motor, probably needs replacement anyway. Before it causes an big issue.

Let me put it another way, when the L16 came out in 1969 the manufacturer sent them out with holes in the thermostats as there was no bypass, they ran out of them thermostats decades ago and parts dealers just cross referenced the part to regular thermostats because they fit the hole, the reason for the hole was forgotten about as the manufacturers put a bypass in the thermostat housing during the Datsun 620.
Personally I would try the hole before removing the head, also if you remove the head and replace the head bolts I would go with an head stud kit, I have never lost a head gasket on an L block since, but the only engines I have with turbos are diesel engines with no aluminum in them(block/head).

Yeah, I've known about air pockets with thermostats for a while. I'm pretty sure I have a relief hole in mine, but I will definitely double check it. In fact, I may play with it first and see if that changes anything.

Also, with the Motec system, it runs at 1500 rpm for like 15 minutes before it finally settles down to 800. I'm just going to assume it's a glitch of the original system. It wants the temperature up and high before it goes to regular. Or it's just cranky because it's old and antiquated.

So I dug through the old pictures for the thermostat housing. Not sure what one is on there now, but I do recall drilling out a hole for the temp sensor....but it was a while back.

They all have jiggle valves to let air out, but that tiny hole is not big enough to let the amount of coolant needed to warm the thermostat enough to open it, by the time the coolant in the thermostat housing is hot enough to open the thermostat the coolant in the head is super heated(boiling) so the thermostat opens all the way and mass coolant circulates until the cooler coolant from the radiator cools the engine and the thermostat closes all the way and it starts all over again, in my opinion the way it is supposed to work is the bypass lets the warming coolant out of the head into the thermostat housing, when it gets warm enough the thermostat opens a little at a time till it finds its happy place and it just runs at that temp all the time, my temp gauge runs right in the middle all the time, but when I removed the bypass that time the temp was all over the place, especially on the freeway(speeds above 45mph).
I told you it was my opinion.
In your photo above it appears you have a big black hose going from the side of the thermostat housing to the intake manifold, do you still have that hose, is it a coolant hose?

At 180 degrees, the thermostat is fully opened. Given the car runs at 190 degrees and the temp probe is right next to the thermostat, it's working if it stays at normal temperature. Now, it could be a sticking thermostat, which I can test after I yank it out and boil it in some water. When the water reaches 180, it should start opening and with prolonged 180, open fully.

The thermostat hole is more than plenty big enough to pass coolant, as seen by the radiator top having the same temperature of coolant as the temp gauge was registering. Don't forget, flow rate is hugely important. If the water pump doesn't have a restriction, it can actually move water TOO fast past the radiator, not allowing enough time for radiant cooling. That's why certain engines overheat WORSE when you remove the thermostat. The water literally goes rushing the past the radiator fins without enough time to shed heat, thus trapping it in the water and completing the cycle much hotter than before.

The big black hose is a water outlet to the cold start bi-metallic spring that makes up the IAC of the original system. It runs from the thermostat housing back to the passenger side water outlet via a metal tube. Both of those have now been removed as I'm not using any of the original air bleed stuff. The Motec doesn't have idle air manipulation ability.

Another thing I figured out is on the dyno, with only one temperature spike, we had the ratios set great. Full throttle was about 11.2:1 or thereabouts. Now, the WOT is 9.8:1. Could be a finicky Motec, but more likely, since the ECU temp sender is right next to the gauge temp sender, the ECU is seeing very hot temps (230) and loading it up with extra fuel to try and cool it.

Thus, I'm pretty certain I have a head gasket failure that's leaching into the cooling passages, not outside the head or in the combustion chamber. Which would make sense on high boost on a hard pull. Either way, I ordered head studs and gasket set.

Final note, the vehicle did this both with and without bypass from thermostat housing, and with original system and the system I'm currently running. Dr. Datsun out!!