car overheating

[Dreco]

Help, My Z is having a problem. Car is cool at idle, but starts to overheat when a load is put on the motor. Has water, Fan works, the pump has only 10,000 miles on it. Does this sound like thermostat? I hope I haven't done any damage to the motor. It happend on the way to work

[kmack]

Two things you may be looking at here:

1) the fan may appear to be working but at speed (w/ the engine under load), the fan clutch may not be engaging and not turning at a faster speed with the engine. This will not allow for maximum cooling and cause you to run a little hot.

With the engine warm or hot (not running), try to turn the fan. If there is little resistance, then the clutch is bad.

2) the cooling passages in the radiator be getting clogged up some. At idle there is not that much heat generated and the limited capabilities of a clogged radiator are still sufficient to keep the motor cool. At higher speeds though, the radiator won't have the capability to flow enough coolant.

With the engine running and warmed up, place your hand on the front side of the radiator (opposite side of the fan). Feel for any spots on the fins that feel "cooler" than the rest of the radiator. This will tell you where the clogged areas are.

[Dreco]

when I put a load on the motor and the temp increases, it increases pretty fast. Temp comes down fast when I let the engine idle. I'm going to throw in another thermostat real quick and see what happens.

[Dreco]

it's not the thermostat. I'm thinking it's the water pump

[Dreco]

I put in a 195 thermostat. It seemed to hold temp. but the needle was very high. the needle was just before the 'P' on the gauge. The one I took out was a 160 degree ( found that was too cold) with the 160 the gauge read just after the 'T'. I'm just wondering how accurate my gauge is?? One thing I did notice is that where I spliced the temp sensor wire, the electrical tape came off and the bare wire was touching my distributer. I'm wondering if that might have been the cause of my temp peging like that. The radiator never steamed, and the car seemed to run fine, and when I put the 160 degree thermostat in some hot water, it opened fine. Is 195 thermostat too hot?? (or too hot for track?) or should I get a 180? temp rarely gets above 95 where I live.

[kmack]

Sounds like the wire was grounding on the dist. and causing your problem.

I would think the 195* thermostat is a little too warm for use on the track. I used to run an aftermarket thermo (195*) on the track and I could only go for about 10-12 minutes before the motor started running hot. This was on the stock radiator.

I've now switched to a Nissan thermo (185*) and a 280ZX radiator. I can run hard for over 20 minutes now on the track and the needle never moves off the "T".

I also checked my temp gauge using some resistors. 33 Ohms is supposed to put the gauge @ 195*, I believe. There is an article about this in one of the Sport Z magazine issues. I could only get to 32 Ohms. Anyway, at that reading my gauge was sitting right about between the "E" and the "M". So I know for sure that I'm running a little cooler now.

[Dreco]

Thanks for the input. befroe I noticed the wire, I had already thrown in a warmer thermostat (switch from a 160 to 195) I then saw the wire and fixed that too. The temp seemed to hold (although the gauge read A LOT HIGHER THAN WHAT I WAS USED TO) The only reason I used a 195 was because that was the only one I had too swap. I started another thread about what degree of thermostat I should use. My radiator is the 4 row radiator the Motorsport Auto offers. I'm going to get a more accurate temp and decide which thermostat puts my engine temp at the optimum level. (water temp being different than engine or oil temp).

[kmack]

Also keep in mind (if you don't already know) that the Nissan thermostats have a larger opening than the aftermarket ones. Allows for more flow and better cooling.

They're not as cheap as the aftermarket ones, but neither is rebuilding the engine after overheating and cracking the head!

[Dreco]

thanks for the tip. Hey I noticed your from San Antonio. Looks Like i'll be there visiting family for Xmas.

[kmack]

Hey I noticed your from San Antonio. Looks Like i'll be there visiting family for Xmas.

Sounds good, although it has been fairly chilly around here lately (I won't say it's been cold cause the "Northerners" will complain). I'm not planning to go anywhere this Holiday because I may have to work that Friday. Send me a PM if you want to try and meet.