Coolant Temp Warning Question

[miscrms]

Ok, I'm hoping someone can help me understand the cooling system a little better. I have an intermittent coolant temp warning coming on that I definitely need to get sorted before it starts warming up. Here are a few facts/thoughts:

1) Grill top is ~90% blocked, temps have been in the 40s-60s, both times this has happened its been in the 50s. Both times were cruising light duty highway ~60mph no real hills to speak of. Nothing out of the ordinary in terms of route or trip length.

2) When warning comes on its very uncertain about itself. Sometimes clears before it even gets around to telling me what the error is. Never stayed on for more than a minute or two. Definitely clustered though. On one occasion I got maybe 10 occurances in ~5 min. On the second, it only happened maybe twice, several minutes apart, then quickly went away.

3) No visible/audible symptoms of actual overheating. Put heat on Max Hot full blast, air was not hot. Stopped and opened hood, no hissing, no extreme heat radiation from engine compartment. No pinging.

4) I've never really taken note, but as I think back it seems to me that every time I have looked at coolant reservoir its appeared empty. Even after taking it in for service. Since it is an odd shape/size and had no sort of "full" marking I could find, I assumed this to be normal but it did seem odd. Owners manual seems to indicate it should be "about half full", is that right/common?

5) I noticed a while ago that a black hose seemed to look somewhat out of place lying on top of the coolant tank. Didn't see any obvious place for it to plug in, assumed it was a breather or something. On closer inspection, I now realize its supposed to plug into the cap on the coolant tank, but the nipple has broke off. I'll have to see about getting the cap replaced, but the tank doesn't look like a traditional sealed expansion tank so I'm not sure that's related. Either way, I'll have to see about getting a replacement cap.

6) Inverter Coolant tank is full.

7) I have only a very generic/cheap OBDII reader, have not tried scanning yet. Is it likely to say anything more informative than "coolant temp high" if that?

8) Both times this happened were within a week after most recent dealer routine service.

Thanks very much for your thoughts & comments.

Rob

[jayman]

The first thing I would suggest is removing the grille blocking altogether, then see if the problem replicates. If not, the temps and driving were probably a bit too warm for the grille block

My inverter coolant tank is near the top, slightly past the Full mark. The engine coolant tank is around 70% filled. It helps to check in a dark place - inside a garage or at night - by using a flashlight.

Put the flashlight directly onto the engine coolant tank the level should be at least 50%. If it's less, that could mean a leak or never properly filled

The cap on the engine coolant tank should have two hoses, one goes to the motor and rad, the other is a short overflow tube that goes alongside the tank. If the cap is damaged, it's possible the engine has been allowed to run with air in it.

Note, the actual rad cap is under the plastic trim pieces between the front cowl and rad. You have to take that crap off to see the cap itself

[JimN]

Rob, has the fan turned on? This is a situation where I would err on the side of caution. I would pull the insulation although I don't believe it is a factor and take the car to the dealer. If the fan is off and the light isn't on steady I don't think it's overheating but something isn't quite right.

For example, last week the low coolant light on my Intrigue stayed lit for a few minutes. The coolant in the recovery tank appears to be a bit low. The light hasn't lit since. I'm changing the coolant since it is due not because I believe the idiot light indicates a problem.

[seasalsa]

Rob,
Have you read this thread on grill blocking cautions?

http://priuschat.com/forums/prius-mo...g-caution.html

[edthefox5]

Be careful there as it is hard on the block to have repeated heat spikes. You could damage the head gasket or worse. Plus with no gauge you don't know how spiking it's getting. If it was me I would check the water pump to see if the weep hole is leaking. The bearing could be going on the water pump. You don't mention you maintenance routine. When was the last time you changed the coolant? Whats it look like if you open the cap to the rad not the coolant recovery? Whats the miles? If the coolant recovery tank is repeatedly low you got a leak somewhere.Period. First culprit is weep hole. Do you smell coolant ? If no leak and your spiking one of the electric rad fans as mentioned earlier is probably bad. Easy to check that. One fan is cooling and the other is ac assist. Put on the ac on full blast after car is thoroughly warmed up and look under the hood and both fans should be running. But if a leak get that fixed asap.The one thing I dislike about our cars is no temp gauge. I would guess by the time the temp light comes on full time its done some damage.

[miscrms]

Thanks for the comments. I will certainly pull the grill block and see if that helps. It seems like I am losing coolant somewhere, so we'll have to track that down. Beyond that, I guess we'll have to see.

Rob

[jayman]

Originally Posted by JimN

For example, last week the low coolant light on my Intrigue stayed lit for a few minutes. The coolant in the recovery tank appears to be a bit low. The light hasn't lit since. I'm changing the coolant since it is due not because I believe the idiot light indicates a problem.

Jim

There is a TSB out for some GM vehicles with the coolant level sensor in the overflow tank. The sensor can get gunked up and sometimes give a false low reading.

That said, it's also a good idea on GM vehicles to keep the overflow tank higher than the Min level. Otherwise air can get into the system and accelerate corrosion. Some reports indicate the early horror stories of Dex Cool - "Death Cool" - stemmed from this

jay

[jayman]

Originally Posted by miscrms

It seems like I am losing coolant somewhere, so we'll have to track that down.

A 2005 shouldn't be ready for a coolant change unless over 100,000 miles. Do not continue driving the car with low coolant and/or a leak. Aluminum block/head motors are nowhere near as tolerant of low coolant or overheat spikes compared to old fashioned cast iron blocks/heads

The air bleed procedure can also be complicated, due to the thermos used in the Prius. This really isn't a Shadetree mechanic type of procedure. If you have access to a vacuum coolant bleeding system, that is best:

http://www.mityvac.com/info_sheets/MV4535_Info.pdf

I have one at my hobby farm, and the nice thing is you collapse any air trapped in the block or rad.

If you don't have hot air coming out the vents when set to Max Heat, you probably already have air trapped in the system. Continued operation could bugger up the motor, coolant transfer pump, etc.

Get it fixed ASAP

[Flying White Dutchman]

Dont get it!

wy wurry about overheating the prius?
the car sensors will tell you when its time to stop and before there is any damage! thats wat there for!

[Bob64]

Originally Posted by lIon

Dont get it!

wy wurry about overheating the prius?
the car sensors will tell you when its time to stop and before there is any damage! thats wat there for!

the car sensors ARE telling him somethings wrong. The question is why it is intermittent.