Proper Thermostat Performance?

[blacksambo]

Driving in the deeply fridgid Adirondacks last night I noticed something I hadn't before about the water temp.

If I coasted down hill for any distance the water temp guage would noticably drop and heater performance would fall off. If I accelerated up a steep incline the temp would rise back to normal level on the guage and heater perfomance would increase without touching the dial??? Does this sound like proper performance or does the thermostat on my VX need replacing?
Thx in advance.

[tom4bren]

It doesn't sound like your thermostat. It sounds like maybe your water pump may not be pushing as well as it should @ higher rpm's. If you're not due for the timing belt/water pump change yet & want to explore a cheap solution, deermagnet has a thread on a pretty trick supplimental thermostat installation that may help you out. It's all external to the head so you don't have to tear into the OEM thermostat which is a PITA to replace.

[blacksambo]

I'll look for it thanks.

[tom4bren]

Holy Carp! It looks like he deleted all the info in that thread. This looks like the one he used though:

http://www.summitracing.com/parts/MEZ-WN0072/

[VxSport]

I wouldn't think it would be the thermostat either. When our vx needed a thermostat it was consistantly running about 25% cooler than normal operating temp. Thus the Stat was opening too early (too low temp). Aweful to change stat by itself.

Your problem sounds like it would be the water pump, because of the changing with the rpm's and loads. What is the condition of your Serpintine Belt that drives the pump?

Good luck

[tom4bren]

IIRC, the water pump runs off of the timing belt, not the serp. Correct?

Not that it makes any difference on how it functions. It's just that you can pop your hood & look at the serp. You'd have to remove the cover to inspect the timing belt.

[blacksambo]

My temp runs at normal when operating under load. It falls to below normal when coasting down hil at 60 mph, in single digit ambient temperatures. Besides don't water pumps either work at full capacity or not at all? My timing belt was changed in the last 10K , and I have no coolant leaks.Thx

[tom4bren]

Did you replace the water pump when you replaced the timing belt? It's recommended.

I was told in the past (not sure I believe it though) that the fins on a water pump can erode over time/use. If that were to happen though, I'm guessing that it would show the symptoms you describe.

[VxSport]

My Bad... sorry. you are correct. Timing belt not the serp. Not enough coffee yesterday.


IIRC, the water pump runs off of the timing belt, not the serp. Correct?

Not that it makes any difference on how it functions. It's just that you can pop your hood & look at the serp. You'd have to remove the cover to inspect the timing belt.

[blacksambo]

Did you replace the water pump when you replaced the timing belt? It's recommended.

I was told in the past (not sure I believe it though) that the fins on a water pump can erode over time/use. If that were to happen though, I'm guessing that it would show the symptoms you describe.

Water pump is original. But maybe I'm dense, but why would less rpm cause lower water temp. to occur? Thx

[VxSport]

It seems that quite a few people have had overheating issues with their Vx's. Others have replaced almost all of the cooling components, before I am quessing tripping over the fix for the problem. Other have fancy new radiators, and didn't fix the cause. I remember others talking about water pumps and also fan blades specificaly the fan clutch.

On our vxsport, for a long time I wondered if our oem temp gauge worked properly. It would go up to about 35% (needle sweep) and just stay there. It was a little low, however for years it would never go up higher. Most of my engine is original. Timing belt and water pump are on my list over the next month, before Moab.

[blacksambo]

Mine is not overheating but rather under-heating while coasting downhill, if there is such a word?

[tom4bren]

Water pump is original. But maybe I'm dense, but why would less rpm cause lower water temp. to occur? Thx

Cavitation. Been through it with the impeller on my SeaDoo. It runs fine at idle but more & more efficiency is lost as the speed increases. Basically the pump could be causing an air pocket to form in the pump restricting flow at higher rpm whilst at idle everything is working fine.

The reason that we usually don't see erosion of the pump blades is that the seals usually fail long before that occurs.

I'm not sayin that your pump is bad ... it's just one of the possibilities to consider.

[blacksambo]

Thx. I get it. Cavatation that is. But at idle my temp drops?

[VXorado]

Cavitation. Been through it with the impeller on my SeaDoo. It runs fine at idle but more & more efficiency is lost as the speed increases. Basically the pump could be causing an air pocket to form in the pump restricting flow at higher rpm whilst at idle everything is working fine.

The reason that we usually don't see erosion of the pump blades is that the seals usually fail long before that occurs.

I'm not sayin that your pump is bad ... it's just one of the possibilities to consider.

I agree with Tom that this is probably a water pump issue. I've heard of similar problems when air is the system- caused by cavitating or not. I would start by burping the coolant system of air. There's a couple easy ways to do this and it's a good place to start. If the problem is fixed but comes back, then it might be time for a new water pump.

[blacksambo]

So, how do you get the air out? Thx

[tom4bren]

http://www.ehow.com/how_7369_burp-cars-cooling.html

& this one makes a good point that you should have circulation through the heater core while performing this process.

http://automotivemileposts.com/garage/v2n15.html

Most cars are 'self purging' & you don't have to worry about it. Since the closed loop cooling system has been slightly modified with the overflow reservoir to still be closed loop (no air can get in) but have open loop benefits (allow for fluid expansion without letting air in).

Some cars do have problems in the design. Mitsubishi Eclipse is notorious for trapping air behind the thermostat which will keep it from opening. In that case I was able to burp it by removing the temp sensor (which is right where the bubble gets trapped) & put it back in while anti-freeze was dribbling out all over my hand, running down my arm, & dripping onto my leg - point being: don't do it with a hot engine:). All of that is irrelevent since you aren't working on my Eclipse but it is good background info for you.

Since I don't recall any VX owners complaining about having to burp their cooling systems, I don't think that this is your problem. But ... it's easy/cheap to do before you start tearing into your water pump or thermostat.

BTW, some parts stores sell a burping kit that is just a funnel that goes on & fits tight where the radiator cap goes. It allows excess coolant to replace any bubbles that escape & not allow any air to get back into the system. I don't think that you'll need that though.

[blacksambo]

I guess you feel I don't need to burp in this instance?

[tom4bren]

Burping always feels good so go for it:)

It doesn't cost anything & has a 15% chance of solving your problem. I'd give it a shot.

[blacksambo]

My radiator is full up and the expansion chamber half full, so I really can't add any but will watch with cap off when I cold start. Thx

[Jolly Roger VX'er]

Some cars do have problems in the design.

I thought my Fiero was tough to burp 'cause the engine is in the rear and the radiator is up front....lots of piping inbetween!

Also...when changing a heater core (general...non-VX specific) I've found it better to fill the bottom heater hose with funnel..connect to core...fill core to top with funnel...fill top hose with funnel....connect to core. This helps reduce chance of developing large air pocket in a new heater core which if happens you are stuck with waiting to burp itself.

sorry....back on topic!

[blacksambo]

I've read elsewhere(Audi site) given the extreme weather that I'm operating well within tolerance. I'll live with that. Thanks just the same.