I'm scared

[BadDog]

Made 2 changes to the car this past weekend: I had the oil changed (was really low!) and fixed my heater by hooking new hoses up (the PO had blocked the hoses off coming from the engine) after one of the caps blocking off the system went all to hell... (I topped off the radiator with a 70/30 antifreeze/water mixture, warmed the car up, and topped off again)

I have heat now (woohoo!), but my my engine is running a lot hotter (maybe the hoses are on backwards?!?!?!).

Also, when going from driving to idling, my oil pressure drops down to *past zero*!

[2ManyZs]

Well, as far as the oil pressure problem. First thing to do is to change the oil pressure sending unit or verify the oil pressure with a mechanical gauge in place of the electric one.

Doubt you would have heat if you hooked up the hoses wrong so that is probably not the problem. Since it is probably warming up (even in NY state), you might want to check or replace the thermostat just to be on the safe side. Of course a new sending unit there might be the culprit too, hard to tell how much corrosion is on it, or if it has ever been replaced. Best to start with the obvious, before we go to the other causes.

It could also be your mixture of antifreeze and water, most of the time a 50/50 mix is recommended. It is possible to get too much antifreeze in it and it will not cool as effectively.

[AxtellZ]

I agree with Keith. A 50/50 mix will cool better, and offer the best protection from corrosion in the innards of the engine.

Agreed with the oil pressure too, though it is weird that it acted up after an oil change, when it had been fine. Seems that most z cars aren't particularly accurate to begin with, and many show zero pressure at idle. A mechanical check sure as hell won't hurt, but it sounds fairly normal.

Oh yeah, Redline "water wetter" added to the coolant will drop your operating temp around 10 to 12 degrees, i'm told.

HTH, Jeremiah

[Mike]

Originally posted by BadDog

but my my engine is running a lot hotter (maybe the hoses are on backwards?!?!?!).

Also, when going from driving to idling, my oil pressure drops down to *past zero*!

Baddog,

I took out the most important part of that explaination. Your engine is running hotter and your oil pressure indicator is low.

Something is fishy here. Make sure you used the right oil filter, oil, and you added enough oil.

I had the same reading on a car I just started (after it sat for over 15 years) and I blew the head. I think it was due to low oil pressure, but, I can't be sure about that yet.

I don't want to spook you... but, just double check everything you did. And, also check that connection to the oil pressure sending unit. It's a little electric device screwed in to the engine block. It's got a single wire and it's located just to the right of your dipstick.

[BadDog]

Thanks, everyone. I drove her around my neighborhood this morning until it warmed up all the way. She didn't get as hot as she did Wednesday, but it was also a little over 80F Wednesday, and about 70F this morning. The temperature registered right in the middle, where as Wednesday it was about 3/4 of the way towards the red (used to run at about 1/3, but it hasn't been this warm out since I got the car in March!).

When I let her idle for a few minutes in my driveway after driving around this morning, I kept an eye on both guages, just in case. The pressure would read at 20 lbs or so (estimate), and the temp went just a hair over the middle. So, I drove her to work (30 miles) and she behaved about the same, but the temperature stayed the same, too.

I checked the hoses again last night: The short hose from the rear of the block goes into the heater core's valve, with the return hose going up front to the block side of the lower radiator hose.

I thought that 70/30 would cool better; I thought that the role of using Antifreeze was to "center" the boiling/freezing properties of the water: lower the freezing point and raise the boiling point (in conjunction with the collant system's pressure). If you guys think that more water in the mix will help, I'll try changing the ratio :-)

I'm using 10W30 oil. The oil pressure was fine all afternoon, then I hooked up the heater core and (because I had "sudden coolant loss") filled up the cooling system after testing just the heater core and new hoses with water from a garden hose.

I was wondering if my water pump was having trouble with the extra volume now that the heater is hooked back up, but that doesn't make much sense because the pressure should still be the same. If anything, the water pump may have been damaged due to the loss of coolant when the cap on the rear of the block started leaking.

I think I also need to install a radiator shroud.

As for the oil pressure dropping to below zero on the guage that night, it may have also been in part because my car was only idling at about 500 rpm (having trouble getting the timing set, I think my cam timing is WAY off ) The idle is better after bumping up the air a little and advancing the timing some more...

On the bright side, is anyone here going to the car show this Sunday? "Sports Car and Vintage Auto Festival" (aka the Victor Show) It's at the Finger Lakes Race Track. I'm gonna try to make it, either with my Z or my daily driver. There should be a healthy number of Z's there from the 3 upstate NY clubs. It's billed as the "biggest 1-day car show in the Northeast". I guess last year so many Z's showed up they had to create a new class

[AxtellZ]

ZCCR (z car club of rochester) has i think 20 confirmed entries to go. I'm not positive, as i am taking my yellow 260 to a local show on Saturday (which happens to be my wife's birthday). She may not be totally gung-ho on 2 car shows in one weekend as a birthday present....(but i sure would!)

I'll work on her- if you see a bright yellow 260 with sunroof & black interior- come say hi! Oh, and look for a white 73 license plate "1 tuff z" Thats Dave Palermo, our club president got an L28 with a JCR supercharger..nice ride!

Zya, Jeremiah

[2ManyZs]

A fan shroud will help a tremendous amount. It will allow the fan to pull more air through the radiator especially when you are sitting still or in slow speed traffic.

Timing that is too far advanced will also contribute to running a little hotter than normal.

If all else fails you could try a 160 dgree thermostat.

If my memory serves me correctly the hose that goes to the heater control valve should come off the Y in the rail along the side of the block. The return hose is the short one that goes to the back of the head. This might be part of the problem, I think you do have them backwards and are trying to force water against the flow. The line coming from the lower radiator hose is the line that feeds water to the block and should also feed the heater and the intake/carbs.

Diluting the mix wouldn't hurt, just drain a little out and add a quart of water to it.

The oil pressure drop probably was due to the low idle, but installing a new sending unit would add to a little insurance that everything is working right.

[billcapp]

Oh yeah, Redline "water wetter" added to the coolant will drop your operating temp around 10 to 12 degrees, i'm told.

HTH, Jeremiah

water wetter will leave a residue in the radiator

[BadDog]

Jeremiah,

If you see a silver '73 with a cracked dash on the field but not being judged, that's me :-)

2ManyZs, as always good advice :-) I hooked up my heater hoses based on the old (braided) ones that were still there, but just cut, and the cooling system capped off. The short hose was contoured to line up with the rear of the block, went in the higher of the two holes on the firewall, and was hooked up to the valve. The longer hose was too long for the rear of the block and was hooked up to the back/side corner of the heater core.

Can anybody go take a look at their hoses and let me know for sure if they get a chance? Thanks! :-)

[EScanlon]

At the risk of sounding like a pompous overbearing self-righteous old coot, (may I are one at 46), let's apply the K.I.S.S. principle here.

I had the oil changed (was really low!)

Do you know when the oil AND filter had been changed before you did it this weekend. I'm presuming that you had the filter changed, if not then I'm also guilty of the "arse-U-ME" principle.

If it's been a while, then it is very probable that the NEW oil has loosened up items that were caked / gunked up before. One of which could very well be the oil pressure sender unit. Conjecture, but nonetheless, in other oil pressure gauges where an actual pitot tube of oil went to the gauge, an air bubble could cause the most outrageous of pressure differences, that could be the case here.

but my engine is running a lot hotter (maybe the hoses are on backwards?!?!?!).

Even if they were they wouldn't cause the engine to run hotter. The only effect would be that you would have a Fully hot heater core inside the car interior that is allowed to release ALL of the heat it gets from the engine inside the car, and the return to the engine is restricted. The normal method of operation is that the Fully heated coolant is outside the car interior; restricted from entering the heater core at full volume.

In both instances the return volume from the heater core would be regulated by the heater control valve, and since this either shuts off or opens all the way (as well as stages in between) it has no direct bearing on the heat of the engine. (Although, in an emergency overheating situation, if you turn on the heater valve and allow the heater core to act as a second radiator it CAN help reduce the heat of the engine)

The oil pressure sending units are known to be inaccurate and are an item that can go bad. I would try to get a new one and see what that does, or check it with a mechanical one.

The thermostat may be something to check in to, but I would FIRST address the timing as 2MZ pointed out, then I would check the thermostat if the timing does not change the temp.

By the way, the 70/30 mix of AF/H2O is for increased EXTREME TEMP protection. i.e. it will allow your coolant to NOT freeze or boil until it reaches lower / higher temperatures respectively than a 50/50 mix. This has NOTHING to do with it's effectiveness as a cooling agent, in fact it may affect it's heat exchange properties. i.e. how easily / quickly it gains / loses heat energy. And THAT property is what determines how good a coolant it is.

Just my 2¢

[visionary]

Hey Baddog,

I doubt there is a 240z.org member that would not support the following statement.

The sending unit for the oil pressure gauge on the L24 engine is a piece of crap.

You can replace the unit. I have read various accounts of junk yard and aftermarket parts replacements of the sending unit, however they all end with the same ending; the unit fails again.

I replaced my oil pump with the turbo version from MSA and it did make a slight difference at the gauge. I have a parts box with 4 old sending units from previous owners, so, I haven't bothered to replace the crappy one on the engine currently.

It is devilish how the mental effects of a needle that does not move play havoc with grey matter. Like I said, I had to replace my oil pump with a turbo pump before I felt comforable. The actual problem is the sending unit.

I did see a VDO sending unit last week that I will most likely end up buying ($35.00), but, once again, that is only for my mental stability...

Keith

[BadDog]

EScanlon: well spoken as usual

visionary: ROTFL

I haven't followed up earlier than this because I've spent all day getting my car ready for that show tomorrow... I think I'll let it be judged in the "daily driver" category after all... can't hurt, right?

Anyway, I've altered the ratio, and my car is definitely running cooler now :-) And now that it's running cooler, it maintains oil pressure when idling when warmed up (about 1/4 to 1/3 from the left).