87 prelude runs hot in heavy traffic

[TallGuyCA]

Hi,

I am new to this group and this question may have been asked before.

My'87 prelude SI runs great but in heavy stop and go traffic the water
temperature goes way up at 80% and then the fan engages and cools it down to
50% levels. In normal driving it is stable at 30% of the gage.

This has been happening for couple of years and I am wondering what could be
wrong. In the past the hottest the engine got was at the 50%. My mechanic
friend said that it is the fan switch. I had it replaced and the problem
persists.

Is there a thermostat that needs to be replaced? Could it be a sensor
somewhere else that is broken? I just replaced the vacuum next to the
distributor and oxygen sensor during a smog check.

The car has 190,000 miles on the odometer and I have been the sole owner of
the car.

Thanks for your help in advance.

[wdb]

Hi,
If the fan engages only after the engine reaches, as you put it, 80% on the
gauge, then it is the thermostatic switch controlling the fan. Now, if the fan
is on and the engine still stays too hot in traffic, I'd check the radiator core
for a build up of bugs, and or debris causing reduced air flow through the
radiator. From what you are saying, that the car is fine at highway speeds,
lends me to believe the radator, water pump and all are fine. It is the fact
that the fan is waiting till the engine is too warm befire it comes on, thus the
reason why your temperature rises a lot,t hen drops back down when the fan
starts to work. I would strongly suggest finding out exactly what is in the fan
switch circuit by purchasing a manual with an electronic diagram of this
circuit. Find the part that senses the coolent temperature and replace it. With
the miles on your engine, it is not unreasonable to assume that this sensor has
become unreliable. Most all vehicles out there will run at the correct
temperature even with a completely dead electric fan as long as you keep your
speed above 35 mph. The only time most cars will actually use the fan is when
you are moving slowly in stop and go driving. In fact, the fan will cycle on and
off if you are sitting and idling the engine.
Bill B.

Post by TallGuyCA
Hi,
I am new to this group and this question may have been asked before.
My'87 prelude SI runs great but in heavy stop and go traffic the water
temperature goes way up at 80% and then the fan engages and cools it down to
50% levels. In normal driving it is stable at 30% of the gage.
This has been happening for couple of years and I am wondering what could be
wrong. In the past the hottest the engine got was at the 50%. My mechanic
friend said that it is the fan switch. I had it replaced and the problem
persists.
Is there a thermostat that needs to be replaced? Could it be a sensor
somewhere else that is broken? I just replaced the vacuum next to the
distributor and oxygen sensor during a smog check.
The car has 190,000 miles on the odometer and I have been the sole owner of
the car.
Thanks for your help in advance.