1998 Volvo S70 GLT Overheating RESOLVED ECT

Teslacoilftw · Post by **Teslacoilftw** » 16 Jul 2013, 19:21

So over the weekend, I replaced the Thermostat with a Moto-Rad 192 Degree "failsafe". I replaced the Sensor with a Genuine Volvo Sensor I purchased from Volvo. The reason why I did this was because my Volvo was attempting to overheat and I was having some hard starting issues. Once the car started and ran it was fine. I have already replaced the MAF and since the MAF replacement I have since resolved a few other throttle problems I posted this a few weeks back. Now the over heating issue; It's never redlined. Watched a Youtube Video on how to replace the thermostat and it literally only took 20 mins. However my issue with the Hard starting has not been resolved unfortunately. Basically it acts like its going to start and then it either does start and it sounds groggy or Like today it started and then died. Also the over heating issue hasn't been resolved I thought it was just a fluke. After the installation I ran it for 15 minutes with the heater on and the coolant Cap off allowed it to warm up and come to temp Replenished the fluid to "Max" (Basically topping it off) I didn't loose but 4-5 ounces when I replaced the thermostat. The Volvo heated up like its suppose to stopped in the middle the fan kicked on I thought everything was good to go. Except yesterday I was in Heavy Traffic and the car's temp started to rise again got to about 1 bar from Red and I heard a strange hissing noise with a slight pop and then it started to go down again. I'm guessing that was the "failsafe" mechanism. When I did the replacement I didn't see any frayed cables or anything coming off the sensor. The fan does work when the AC is turned on and I've seen it work while the AC was off in the last couple of days.

My question is why would it work randomly?

Anybody have any ideas on what and How I should go about checking this. The good thing is this isn't my primary Mode of transportation.

As always I am greatly humbled and appreciative of every ones Wisdom that is provided.

Post by **jimmy57** » 16 Jul 2013, 19:37

Your fan could be running on the high speed and skipping the low speed. The small wires at the cooling fan relay in the two wire connector are for low and high speed. The insulation on the terminals keeps the wires in the connector in correct position. The insulation over the terminals can crumble off and only one speed will work. If it high then the gauge will go up before fan runs.
The failsafe t-stat shouldn't make a noise. It is designed so a failure leaves it open instead of closed as with the OEM design.

The starting problem sounds like fuel pressure loss when engine is off. Put a fuel gauge on the schraeder valve over by throttle cable spool and see if pressure doesn't drop below 30 psi in 20 minutes.

Teslacoilftw · Post by **Teslacoilftw** » 16 Jul 2013, 19:52

jimmy57 wrote: The insulation over the terminals can crumble off and only one speed will work. If it high then the gauge will go up before fan runs.
Thanks I'll look into this....

The starting problem sounds like fuel pressure loss when engine is off. Put a fuel gauge on the schraeder valve over by throttle cable spool and see if pressure doesn't drop below 30 psi in 20 minutes.

I don't own a fuel pressure gauge. I'll look into seeing how much they cost. Or is there another way to test this theory?

Post by **E Showell** » 17 Jul 2013, 11:24

Last time I heard a hissing sound and a pop they were in the reverse order and a hose clamp let go and emptied my radiator in a parking lot. I shut that engine down before the steam cloud stopped rising off the cold parking lot surface.

Post by **cn90** » 17 Jul 2013, 12:05

- Next time use Wahler thermostat. Motorad "fail-safe" tstat can be troublesome. Google and you will see what I mean.

- Your symptoms of hard starting is consistent with bad Engine Coolant Temperature Sensor (ECT). Use only ECT from dealer ($40). No aftermarket part. Info on ECT is in forum, search for it.

Post by **rspi** » 17 Jul 2013, 14:19

He said he got the ECT from a Volvo dealer.

I'm with Showell on the pop hiss sound. Sounds like something blew. Do you still have coolant?

If the car is trying to over heat, something is wrong. The system is simple, water pump to circulate coolant, thermostat to allow hotter coolant to go to the radiator, fan to cool the radiator down when it detects it's hotter than it should be, yada, yada, yada.

If the car is actually getting hot, there is likely a problem with one of 3 things (if the coolant level is correct and not leaking out):
1. Water pump is failing or has failed. I have seen propellers off of the pump lying inside the motor.
2. There is a coolant blockage (very rare).
3. Indicator is bad, thus your change of the temp sensor.

Other than that, you DO NOT have to turn on the heat with these cars because the coolant flows through the heater core all the time. You should NOT run the car with the coolant reservoir cap off, the system is suppose to be pressurized and needs that cap on.

Not sure if this test is 100% or not but, you may be able to test to see if the water pump is working by pulling the thermostat and starting the car with the housing and thermostat off. You should she a lot of movement or coolant bubbling at the housing because the pump is trying to circulate the coolant. If you see no movement and it doesn't try to come out of the hole, the pump is likely broken internally.

Post by **precopster** » 17 Jul 2013, 15:20

The coolant may always run through the core, however turning on the heat and placing fan on high allows for large amounts of heat transfer to take place therefore slightly lowering coolant temps (just have windows down if you don't like suffocation)

You can check this with a Scanguage or Torque .

+1 on checking the water pump.

Thermostats can remain stuck closed. At the very least replace thermostat ( you can't remove it and seal the housing because the thermostat body forms part of the seal) You can gut the centre of the thermostat out for testing. This would totally eliminate the possibility however slight that the new one is also faulty (rare but possible)

Post by **rspi** » 17 Jul 2013, 19:32

I have not tried that with my Scangauge. How much do you think the temp will drop by running the heater full blast?

Post by **precopster** » 17 Jul 2013, 21:08

At steady 30mph on flat roads on a cool to mild day it just dropped from 99C to 90C so a good difference.

Can be the difference between a boil and non-boil. It's a smaller area than a radiator but still capable of sending off a lot of heat.

Post by **precopster** » 17 Jul 2013, 21:27

All Volvo white blocks will overheat if the fan doesn't come on in time and if the coolant is not a 50/50 mix with de-ionised water and pure coolant, especially while idling in warm weather. Cheap/diluted coolant with low concentration will cause problems in hot weather.

Check your car with a ELM-327 connected to laptop with software (or Android bluetooth device) the fan should come on at 105deg C and lower the temp to around 96degC (sorry do your own conversions to F here)

If this isn't occurring replace the fan relay.