1998 S70 Engine Temp Fluctuation after Tstat and ECT replace

westroxvolvo98 · Post by **westroxvolvo98** » 23 Jun 2014, 06:37

Hi All,
I am pretty new to the forum but have found some great information here over the past few months.
I have a 1998 S70 GLT with about 176K on it.

Interestingly, I had a Tstat failure about 6 months back and replaced with one from Advanced Auto for a quick fix. Last week I overheated on my home from work, my radiator had a slow leak so I thought my coolant level had gotten too low and that causes my issue.
So I replaced my radiator and most of the hoses thinking I should be all set.
On my home, I overheated again. So I bought another Tstat from Advanced Auto, popped that in and I was all set. I drove the car to work Thursday and Friday without issue, Engine temp level was perfect.
Knowing that the Advanced Auto Tstat had failed on me once before, I decided to head to the volvo dealership and grab a genuine Volvo Tstat and ECT sensor and I installed them on Saturday. But didn't get a chance to take the car for a good drive until this morning's ride to work.
Now my engine temp is fluctuating around and I heard the Fan running immediately after the car started from a cold start. I am suspecting the Fan Relay module but it seems too coincidental that all these issues would pop up at once. Does anyone think it could be the new ECT or possibly the connector?

Any help would be greatly appreciated.

Jim

Post by **rspi** » 23 Jun 2014, 08:13

Hi and welcome to the forum.

Yes.

On another note, these cars are very unforgiving with overheating. You need to check for a blown head gasket. These cars run very well with blown head gasket, however, they usually force coolant out of the top of the coolant reservoir while driving. Check the level before you start cold, then again after 10 minutes of driving. If the level raises in the reservoir, you likely have a blown head gasket. Make sure your cap is not cracked.

Post by **Ozark Lee** » 23 Jun 2014, 08:16

Check the connector on the ECT sensor for signs of corrosion and make sure it is fully seated. It is fairly rare for new Volvo parts to be bad out of the box but you may have a dud. From the sounds of it, your fan relay is OK and it is just doing what it is told to do. The normal failure mode for the fan relay is to do nothing.

...Lee

Post by **cn90** » 23 Jun 2014, 08:34

- Tstat: I use Wahler brand only.

- ECT is likely bad. If you use new ECT, stick to Volvo or SWF brand, about $45.
Info in forum, it is a bit tricky to replace the ECT.

westroxvolvo98 · Post by **westroxvolvo98** » 23 Jun 2014, 08:35

Guys,
Thanks for the information, hopefully it's not a blown head gasket, I just put about $1500 in parts in the car over the past few months. I was hoping to get another year or two out of it.

I will check a few of these issues and let you know.

Jim

Post by **mecheng** » 23 Jun 2014, 08:45

How long did you drive with it overheated? Did the temp get into the red? Always watch that gauge.

westroxvolvo98 · Post by **westroxvolvo98** » 23 Jun 2014, 09:39

I replaced the ECT with a brand new volvo one on Saturday.

I did not drive the car long with the temperature in the red. Pretty much pulled over right away and let her cool down.

westroxvolvo98 · Post by **westroxvolvo98** » 23 Jun 2014, 10:52

Just went out at lunch time and cleaned the connector to the ECT, it was definitely corroded and took it out for a ride. Seems like everything is okay, the engine temp gauge came right up to 3 o clock position and didn't budge. The only concern that I have is the that the resistance on the ECT was 148 Ohms with the engine at temp. According to another post it should be 200 ohms at operating temp.

* 90C (Operating Temp): 200 Ohms
* 100C: 150 Ohms

Does this seem like an issue or not?

Post by **mecheng** » 23 Jun 2014, 10:57

Do you have a scan guage that measures temps?

westroxvolvo98 · Post by **westroxvolvo98** » 23 Jun 2014, 11:56

I don't, any recommendations for a decent gauge.