first problem: there is a vibration when driving and the drive line has slack( meaning when I match the speed of the motor with the rear end so the car is not accelerating or slowing down AKA no stress on the dline) anyway it does not vibrate when accelerating or slowing. I checked the drive line the other day and found out that the rear u joint is tight, but the front u joint has about 1/16 on an inch of play. I also noticed the slip yoke going into the tcase has some play. my questing is if I replace the dline is there still going to be play in the slip yoke going on to the spline shaft?

Second problem: when I got it the temp gauge never went to where it should be. I put a new head gasket in the trackick. it didnt change the heat isue. the gauge still went from 0 when I first started it up to 1/4 of the gauge. I think it would mean it only gets up to about 120 max then it stays between 120 and about 80 degrees. my first thought was to change the thermostat. when I took the old one out it was rusty, but it was sealed in there. I put a new used on in that looks good and I still have the same problem.

What do you think?

Problem 1, driveshaft is hanging out too far, get a spacer or do a SYE conversion

Problem 2, sounds like a replacement temp sender, an original one will probably
fix the issue, unless it bothers you, this isn't really an issue

Wild

it is stock, so I dont know why it would need a spacer. the other thing is the heat in the car never comes all the way up, so I dont think it is warming all the way up. will the sensor heat the motor up more?

any movement in a u-joint will cause some vibes.

Ohh, I thought you were lifted, then you have a bad u-joint

Wild

the heat in the car never comes all the way up, so I dont think it is warming all the way up. will the sensor heat the motor up more?

No, the sensor tells you how hot the coolant is, which is controlled by the thermostat,
you could of got a low temp stat that was miss marked or miss packaged, should be either
a 180* or a 192* and the stat should have the # stamped on it around the edge.

Later models had a rubber gasket that fits around the edge of the stat, make sure it's in there
or the stat can't control the temp because the coolant is leaking past and not getting up to temp

What are you driving year and model, this would help to ID the problem too

Wild

i had this same problem with the guage not moving past quarter of the way and some times droppes down to the first line on the guage. it use to stay a little below half then when i replaced the stat it started acting up i did change the sender out for the guage it was one from 16v and it read no higher than a quarter. as far as no heat with mine the heater core was backed up and i had to replace it. it was a bi*+h to do i had to remove the hole dash and blower asembley. thats where i would look first as far as no heat that might even help bring ur temp up. u could bypass the heater core and see if that helps with any thing and u could check and see if the core is stopped up if it is try flushing it out with a garden hose i did that and it worked for a little bit but mine was bad and started leaking a few days later.

it is a 90 Geo tracker LS1, by the way what does LS1 mean? my heater core clogged up after I got it. so I took an air blower and blew air threw it and that has opened it up, and it seem to work now. I don't know if some years have better heating systems then others, but my 93 sidekick had a great heater once it warmed up there was actually way to much heat and I had to turn to heat lever all most all the way to the cold side. I just expect the same thing, but maybe I shouldn't.

The GEO was Canadian built I think, you can check by looking at the VIN
it should start with C if it's Canadian or J if it's Japanese.

I know a 92 GEO had the gasket, and yours might also have it, do you
remember if it was in there? or pull the thermostat housing off and check
to see if it's there or if it needs one, there will be a machined recess for the
gasket, if there isn't a recess then you don't need to worry about the gasket

Wild

my Vin starts with 2cnbj, so does that mean it is Canadian? all that was there was the neck on the top, then the flat gasket, then the thermostat sitting in a little recess. does this make sense? if so , should it have the o ring or gasket?

Yes, if the little recess is deeper than the edge of the thermostat it needs the rubber
gasket, the gasket slips onto the edge of the thermostat, then put it in the recess and
give it a try

Also make sure the hole (air bleed valve) in the thermostat faces forward.

 I went to get a gasket for my other one and the parts guy said there was no option except the gasket for the top. I never knew it mattered if the hole faced in different directions. I just thought it matered what face is up.

FSM says it should face the front.

I will try that and try to get the right seal for it.