[toddshotrods]

A cool dude read this thread and emailed me this:

Hi Todd I read about your heating problem. Check the viscosity of the coolant. If the coolant to water ratio is to high it can cause the liquid to cavitate around the water pump blades at higher RPM cutting down water circulation but not as critical at lower speeds. Cliff………..

I wanted to share it in case it helps someone else with a dino-burner that can't keep its cool.

[E4mula]

The other thing you can run into that has similar symptoms is your head gasket. Combustion gases escaping into your coolant, but not a large enough leak to allow the coolant back into the cylinder. When it happened on mine, it only heated up during acceleration and higher speed driving.

Change your thermostat. It may be working but not opening all the way causing a restriction. It is cheap and easy to do and then go test it. Like was stated earlier, don't go spend a bunch of money on a simple little problem. Do the thermostat first. Don't assume it works properly. I have seen plenty that did not work at all or opened only part way. That would cause a high speed heat up of your system and then cool down after you slow down.

I like that viscosity issue you mentioned. Good information. I will pass it along. I think that would come into play if someone said to themselves that if some anti freeze is good then 100% must be better. Don't laugh, it's been done before. Nice think green gunk. I use special stuff in my VW so it won't corrode the aluminum of the engine or radiator. That aluminum corrosion is nasty and does not come out like rust on an old steel radiator. Modern cars don't do as well with old style antifreeze.


Anyway get that thermostat changed and do a test. One test at a time.

Pete

[toddshotrods]

Originally Posted by E4mula

The other thing you can run into that has similar symptoms is your head gasket. Combustion gases escaping into your coolant, but not a large enough leak to allow the coolant back into the cylinder. When it happened on mine, it only heated up during acceleration and higher speed driving.

I'll keep that one in mind. If that's the case it might be a goner. I know my way around these cars well enough to do it with one eye closed, but I don't want to do it. It doesn't seem to heat up with acceleration though, just sustained highway driving. It is only running about 2000-2500rpm at highway speeds. Stop and go where it revs to 3-4K doesn't affect the temp.

But stop and go is only part time at high rpms. Not the same as consistent rpms where it has time to heat up and not dissipate the heat. Just try it. You will need to change it anyway so go get that one thing and give it a try. Then report back.

[toddshotrods]

Originally Posted by gottdi

But stop and go is only part time at high rpms. Not the same as consistent rpms where it has time to heat up and not dissipate the heat. Just try it. You will need to change it anyway so go get that one thing and give it a try. Then report back.

I was replying to the headgasket post when I listed the rpm/speed thing, because he indicated that his was heating up during acceleration as well as sustained speed.

You posted as I was typing. A partially open thermostat and the water pump consistently pushing more fluid kind of makes sense. I might do the thermostat next. Since it's actually working fine around town, I don't have the motivation to run out there and change it today but I'll pick up the thermostat so it'll be here when I get some motivation. Until then, I'll be entertaining ideas - thanks for all the input guys!

[Woodsmith]

The 'check the water pump' thing was for cavitation, I didn't know it could be checked by testing the coolent viscosity.

We used to find the occasional missing impellor fin. Sometimes it would be blocking the coolent outflow from the pump, other times it would just be 'lost' somewhere in the engine block.

[TX_Dj]

Another vote for the thermostat.

I recently chased down an issue in a subaru outback, we changed the thermostat and it still was overheating sporadically. That engine has the water pump driven by the timing belt, so we saved it for last. In the end, we could not determine any water pressure except for steam pressure.

Once it was tore down to that level, we saw that the w-pump impeller was still chromed and there was no significant play in the bearings.

Two t-stats in a row were bad. Replaced it a third time, and it's perfect.

[TigerNut]

Check your ignition timing, specifically at higher RPM, and use a hand vacuum pump to verify that the vacuum advance is working properly. It may be that you're getting too much timing advance under highway conditions and causing a borderline pre-ignition situation.

This may not apply (or be tougher to verify) if your engine has a fully integrated ignition/fuel injection system but it's worth looking into. If the crankshaft position sensor (on an EFI/crank triggered system) has slipped then your timing may be advanced a few degrees from the proper value, which could give you just a bit better mileage around town but contribute to hot running on the highway.

[toddshotrods]

Originally Posted by TX_Dj

Another vote for the thermostat...
Two t-stats in a row were bad. Replaced it a third time, and it's perfect.

I've actually had that happen as well. I was boiling right along with the coolant until someone on the internet who had been through the same experience suggested it. I dropped the old and new thermostats in a pot of boiling water and neither one of them opened! Number three worked for me as well.

I'm definitely leaning that way for a first step.

Originally Posted by TigerNut

Check your ignition timing... verify that the vacuum advance is working properly... This may not apply (or be tougher to verify) if your engine has a fully integrated ignition/fuel injection system...

Computerized EFI system. It's actually pretty good at keeping things in sync, but your points are duly noted as well.

The increased fuel mileage has been there for a couple years though. There aren't any changes or new syptoms that coincide with the heat issue.