Another new problem since my head gasket blew, coolant temp

[Guest bastaad525]

This one starting to worry me. As the weather is starting to warm up here I'm noticing my car running just a tad bit too warm for my liking.

 

Before the gasket blew, the normal running temp for the motor seemed to be with the needle right around the midpoint of the gauge, a little below on cold mornings, and a little above on the warmest of days. On boost it might raise up to one needle-width above the midpoint. Since the head rebuild, it now runs that warm the on cold mornings, and on warmer days it get's pretty up there, about 2-3 needle widths above the midpoint or roughly 3/5 of the full gauge up. Odd thing is, it runs this temp while cruising at moderate speeds, but cools down if I get on it. However, if I get on boost for more than a few seconds and then let off the temp goes up even further. Im' not sure to the accuracy of my gauge but if it's accurate then I'd say the temps stay right around 195-200 degrees normally and maybe up to 210 after being on boost. I'm not sure what to make of it or why this might have started after replacing the head.

 

I'm using a 180* thermostat, which is about 6 mos old. Further, when we took the thermostat housing off when removing the head, I inspected it and it looked great. My water pump is also only a few months old. The radiator is from the same ZXT that I got the motor from, and is in very good shape. I've replaced the radiator cap. I'm running 50-50 coolant/water. I do have the fan shroud from the ZX as well. Only thing that I can think MIGHT be the cause, maybe it's the fan clutch? The fan definately spins when the motors running, but it seems to be quieter than it used to be... not sure though because I think maybe I've just gotten used to it. I do remember thinking how LOUD the fan was after I replaced the fan clutch last year (I replaced it with a used unit). Now it doesn't seem so loud... is there a good way to check if the thing is good or bad? Never understood what the purpose of a damn fan clutch is anyways....

 

The only other thing I can think to do is swap out the 180* for a 160* thermostat, but to me it seems this would be pointless. Or would it be? If the motor seems to sit at around 200*, then 160 or 180, the thermostat is open fully either way and is not affecting temp anymore anyways, right? A friend of mine with a stock 280z was also noticing his car running pretty hot lately, also with a relatively new 180* thermostat, and says his runs much cooler all the time with the 160*. It doesn't make sense to me, and I dont want to waste the time if it wouldn't help.

 

One other thing, I know that running the 160* would make the car run richer, but what I want to know is, will it run richer across the board? The reason I ask is that when I dynoed I noticed the car started to run a bit lean above 5000rpm... if going to a 160* would help that then that's another point for swapping it.

[Z-Gad]

You may want to run an el-cheapo mechanical water temp gauge into the thermostat housing to see what it is really doing. I don't trust the 30 year old gauges. I thought my 77 ran hot until I hooked up a mechanical gauge to it as well.

[Guest bastaad525]

yeah I dont really trust the gauge as far as being spot on, I guess I"m more concerned about the relative increase, where the needle is definately running hotter than it was before, rather than what temp it's actually running at, though that does concern me as well.

 

Can I get one of these gauges you're talking about at an auto parts store or is it more a hardware store kinda thing?

[Tim240z]

Have you purged all the air out of the cooling system since refilling it?

[Guest bastaad525]

ah... no. I didn't think air pockets were ever really a problem in Z engines? How do I purge the air out? I did run the car with the radiator cap off while warming it up the first time.

[SleeperZ]

You are correct a lower temperature thermostat will not help. If all components are in good shape as you say, you must have a big air bubble in the cylinder head. I've not had that problem with Z engines, but I warped a Honda head real badly by not bleeding the coolant system well.

[Tim240z]

Park the car on as steep of a hill as possible (pointing uphill), or jack up the front of the car. This is to make sure that the radiator filler is the highest point of the cooling system. Fill it until it overflows (with the engine running), then replace the cap. Get it hot enough to open the thermostat. Now let it cool completely. Cold...like overnight. Then recheck using the same method as above. If the radiator is full at recheck, then you're good..

Tim

[Guest bastaad525]

Tim240z - okay, can do. Question though, what if the radiator is NOT full at recheck? Do I need to do something else at that point? Also Tim, you say to fill it while it overflows with the engine running, I just want to verify that I'm doing that step while the motor is still cold, right?

 

Sleeper - yeah but it's nice that every honda I've seen has a bleeder built right into the thermostat housing. Just odd though because I"ve never had any problems like air bubbles in a Z engine.

[slownrusty]

I have had a few bad experiences over the years with not properly purging a cooling system. I used to do all the park in on a hill, jack up the front, watch for bubbles, watch the level the next day, then I said enough is enough and splurged and bought this tool:

 

Cost me $75 hooks up to my compressor and works perfectly! No air even in my cooling system since I bought it and it comes with a variety of fittings to accomodate a huge range of rads. One of the best bangs for my buck ever!

 

Yasin

[Tim240z]

Bryan,

Yes, you fill it while cold, with the engine running. As soon as it starts heating up, the coolant will start overflowing by itself, so work fairly quickly. If at recheck, it's low, then just top it up with the engine off.

Best bet is to get a recirculating catch tank. That soves many of these air problems.

 

Tim

[Guest bastaad525]

Okay Tim, did as you suggested... actually seems to have helped, though I did do it wrong! I jacked up the front, took off the cap, topped it off while running... and let it keep running with the cap off. Of course as it warmed up it was pourin outta there... but I thought that's what I wanted it to do... until it got fully warm and got ready to explode Luckily I got the cap on quick. Then I let it cool off til morning and opened the cap... whew was it STUCK... a lot of vacuum had built up in the system apparently as there was a loud popping sound when I got the cap off... good now I know I have no leaks Of course it was a bit low considering how much I let leak out. Topped it off, drove it home.

 

Well for the first stretch of the way home it was up to it's old tricks... running warmer than it used to before the head swap, but suddenly it dropped down and for the second half of the ride home it was sitting exactly where it used to before the gasket went... so I guess it worked? Well if not I'll try it again the RIGHT way this time just to be sure... gonna write it down this time

 

Tim, I've been putting off getting an overflow bottle for a while now... I know I want to put one on there. I'm running the ZX radiator so it has the little outlet of the filler neck for it. But I get the idea that a regular overflow bottle is not what you're talking about? How do you set up a recirculating catch tank?

[Tim240z]

You just need to find a catch tank that has the outlet from the radiator neck to go to the bottom of the catch tank....that way when the car is hot and it spews out some coolant, it will go into the tank, then it can suck water back instead of air. I am using this one on my V8 Z:

 

http://store.summitracing.com/partdetail.asp?part=CSI%2D930P

[Guest bastaad525]

Yeah I remember seeing that thing in your engine bay, actually thought it was for fuel. Okay, so one of the ports on that thing connect to the small port on the side of the filler neck, where do the other two connect to?

 

Another question... not sure if this even matters. Is it better, when cold, to have vacuum in the radiator? If I warm it to regular temp, then just pop the cap briefly to let out the extra air, then let the car cool and open the cap there is vacuum present in the system... hard to get the cap off and there is a snap when I open it. Or is it better to just have regular air pressure in there when cold so that there is higher pressure in there as it warms up? Think it would make a difference either way?