hesitation/ oil pressure?

[gbabcock]

I've been driving my 260 more or less everyday for the last 2 months with no problems and today, first hot day of the season, it started running strangely: Drives fine until warm, then temp starts to creep up and holds a bit below 3/4 of the gauge (I replaced thermo, temp sending unit and water pump recently). Then it starts hesitating, sort of, pulls fine, then lets back a bit for a sec, pulls fine again, let back and so on. If I turn it off and she cools down, runs fine til warm again. Lastly, all of this got me looking at my gauges and I noticed my oil pressure is fairly low in low gears, say 15-25 and 5 at idle and at highway speeds pressure builds up to midway but it takes a while. Good pressure when she's cold. Oil level is fine, coolant level fine - any ideas? Thanks

[d240zx2]

Your description sounds a bit like impending vapor lock. I don't see anything particularly out of order with your oil pressure readings...mine drops to 10 psi or a bit less at hot idle.

Water temp being a tad high could be anything, but I suspect it may be from a partially clogged radiator since you've address the overtly obvious causes. Have you had it rodded out recently? Overly advanced timing can cause overheating, too, so check that.

FWIW

Frank

[sblake01]

You might also want to check your fan clutch.

[gbabcock]

Think I might have found the culprit - I started running higher octane and now the hesitation problem seems to be gone, runs fine even if a bit hot. The temp is isn't right though. There's no fan clutch as I've got an electric fan, I suppose the next thing to check would be blockages, huh? I don't really know what else it could be - runs a steddy temp on days below 65 and only heats up during idle, though once its heated up, it stays there.

[Nissanman]

If it heats up and stays that way then it does sound like the cooling system is marginal, it simply doesn't have the capacity to recover from a thermal shock.

It might come good with a simple flush and clean but unless you know how old the radiator is, it may need to be reconditioned.

You say you have an electric fan.

How is it controlled?

Does it have a thermostat to turn it on?

If so what temperature does it cut in?

Maybe it needs to be reset to a lower temperature.

If everything else in the cooling system is in good condition, the electric fan normally will only be required after some minutes of low speed driving or idling in traffic.

Another problem is using the electric gauge and trusting it as "gospel".

These things are notorious for being vague at best and downright misleading at worst, especially if the Voltage Regulator that powers this gauge is on the fritz.

Try and get another opinion in regards to what the engine temperature is really doing.

You can use an Automotive multi-checker with a temperature probe or a mechanical temperature gauge as a temporary check.

You just need to fix the sender of either device to the outside surface of thermostat housing so it can read the temperature of the coolant leaving the head.

Borrow if you can:ermm:

[gbabcock]

radiator is relatively new as well. I'll try flushing the system, but it would make sense that something is off with the guage, I'll check with my mech and see if he can test the temp for me next time I'm in. Thanks -

[Mat M]

You may have an air bubble or a few in the cooling system Have you tried bleeding the system?

[gbabcock]

How do you bleed the cooling system?

[Mat M]

Try to find the highest point in the system (for mine, with the slope of my driveway, it's the radiator cap), run the car until it warms up, and the thermostat opens. open the radiator cap and fill the void.

[beandip]

Just running the engine and having the coolant circulate through the thermostat will push any air to the top tank of the radiator. If you added more than a cup of water I would be surprised. when does the electric fan kick in . Any time you are moving forward 15 to 20 MPH the radiator should cool the engine with no fan at all . As long as there is no restriction to air flow. I have seen some electric fan setups actually restrict air flow while not operating. The radiator you said is near new. Is it of a capacity large enough for the engine? A cause of a stumble or hesitation can be from too thin of oil in the dampeners of the carbs. ATF can do this. Try 20wt oil, witch is the recommended oil . If you don't have 20 substitute some 10-30 . Another is a faulty vacuum advance on the Dist. Gary

[EScanlon]

The Sports Roadster 1600 L16 engine has the thermostat mounted at the water tower which is the highest point in the cooling system. This may seem totally unrelated, but one major problem with the L16 engine overheating is due to the thermostat having been mounted up-side down. (By the way, one hint given to Roadster owners is to drill a small 1/8" hole in the thermostat to allow for air to "burp" thorugh. Normal "burping" procedure is to insert a screwdriver and push down on the thermostat spring, which is when owners usually first discover an inverted thermostat.)

Why would this matter? Well, since it is the SPRING in the thermostat that actually contracts and then allows water to flow, if it is on the "wrong" side of the water tower, it will take longer to heat up to opening temperature, and therefore will allow the engine to heat up beyond what the thermostat is designed for.

Not sure if this is the case with the L24/26/28 engine, but if it is....

FWIW

E

[sblake01]

The Sports Roadster 1600 L16 engine...........

That should be R16. When I had my roadster, I used a thermostat that had some type of built in bypass and was referred to as a 'failsafe' thermostat. Mine was actually a 2 litre sroker but it was based on a R16 block with a U20 crank, rods, and pistons and a somewhat modified Datsun RL411 cast iron R16 head instead of the roadster aluminum R16 head. Never had any overheating problems with mine.