Sticky Thermostat or Bad Fan Clutch?

[teleman73]

So I replaced many of the coolant hoses on my van this fall (all the ones that were leaking or weeping) and my van had been running at really good temps all winter and then last week it started to run hot. My commute involves driving up a mountain pass and while my van didn't overheat it was running hot and making me nervous. It has since done that again both on shorter drives and on that longer commute. I've checked my coolant and that's ok so I don't think I have a leak. I was thinking that either my fan clutch is going bad which would mean that my engine's not getting proper venting, or my thermostat is sticking. I know thermostats are more likely to go bad, but my understanding is that they either stick all the way open or all the way closed. If that was the case it would either absolutely overheat or take forever to warm up, neither of which are happening. My only other thought is that maybe my water pump isn't circulating water. I'm not sure what you all think is more likely. Also, how would I would check my fan clutch to see if it's bad.

[timsrv]

Thermostats can stick intermittently (I've had it happen). Usually this is the result of somebody using a product like Bars Leak or Silver Seal, but it can happen on an uncontaminated cooling system. Due to the lower cost and ease of replacing the thermostat, it's just a good idea to do that as a 1st step (consider it preventive maintenance). Just be sure to use an OEM Toyota T-stat. Here's a good thread that should help: http://www.toyotavantech.com/forum/s...n-s-thermostat.

As for checking the fan, here's a good thread about that: http://www.toyotavantech.com/forum/s...g-(fan-clutch)

[teleman73]

Thanks Tim,
As always you're a fantastic resource for working on these vans. I am wondering though, everyone is so adamant about using toyota brand thermostats and I was wondering why it's so important with these vans because on other cars it's never been an issue to use aftermarket t-stats. Thanks for the info.

[timsrv]

I've never had a problem with aftermarket T-stats either........until I owned a van. I took that advice with a grain of salt and it ended up costing me a lot of time to eventually figure out it was the damn aftermarket T-stat. Funny thing was, the Toyota one cost less than the one that gave me all the grief. Tim

[teleman73]

So I got my new toyota brand thermostat and other than spilling a bunch of a bunch of coolant on the floor it went together really smooth. I took it for a test drive today and going about 10 miles on fairly flat roads with a headwinds and it was running at normal temps, but I have a pretty steep 1 mile hill up to my house and going up that it started to heat up got to that worryingly hot stage. I couldn't tell if my fan clutch was engaged but then right before I pulled into my driveway the fan clutch roared to life when the temp needle was maybe 2-3 needle widths from the red zone. I stopped and quickly the temps cam back down to normal. This makes me think that it is my fan clutch and that maybe the coil spring that reacts to the heat is starting to go bad and so takes more extreme temps to engage. What do you think? If it is my fan clutch are aftermarket ones ok, or is this one of those items that the toyota part is needed.

Thanks

[originalkwyjibo]

You should read this: http://www.toyotavantech.com/forum/s...ght=Fan+clutch It should answer all your questions.

[teleman73]

Thanks for that link, I've read it before, but I had forgotten some of the more pertinent points. So I inspected my fan clutch as well and there is no silicon leakage (it's still shiny and silver) so is it possible that the bi-metallic spring is fixable or adjustable to react at a colder temp? Or can I get a new bi-metallic spring? Also if I do need to just replace it at 75 dollars for the OEM part, is it worth it at that point to put in an electric fan instead. What would be the advantages or disadvantages of an electric pump?

[timsrv]

What would be the advantages or disadvantages of an electric pump?

Assuming you mean an electric fan, that's not for everybody. Cost of parts & having the shroud fabricated would be a lot more money than replacing the clutch fan.......then there's the set-up time, wiring, etc (assuming you can do that yourself). Even if your thermostat wasn't the culprit, in my mind replacement was necessary in order to rule it out (at least now you know for sure that the t-stat is okay. Assuming you've already checked the obvious things (like debris built-up on the front of the radiator, fan shroud complete & in place, correct ratios of coolant/water, etc) the next thing to do is replace the clutch fan. $75 might seem like a lot, but it's nothing compared to what you'd pay to have a mechanic do it and certainly not as much as replacing an overheated engine. Sometimes chasing these issues comes down to the process of elimination. Don't fuss around trying to save money, just do it. If a new fan clutch doesn't solve, then put your old one on the shelf as a spare. Next step would be to pull your radiator and have it cooked-out & pressure tested by your local radiator shop. If it fails their evaluation, have it recored.

Don't forget these vans have been in service for the better part of 3 decades, so unless you know history on these parts, it's best to just replace (whenever in doubt). You could fuss around trying to fix the old clutch fan or whatever (I understand as I went through that phase), but experience has taught me to just replace and move on. These parts typically only last around 150k miles anyhow, so if your van already has that many miles on it, it's not worth taking the risk of getting stuck out........especially over a $75 part. BTW, nothing in this post is meant to insult, just my humble opinion......take it for what it's worth, and good luck . Tim

[technocj]

How long has it been since the radiator in your van has been removed and flushed? I am always surprised by the amount of debris that builds up, and restricts coolant flow, after 3-4 years.

[teleman73]

Tim, Thanks for the reply, I totally get that the sensible option is to by the Aisin Clutch and be done with it, but as a life long tinkerer I always like to fix things when I can so my question about the spring adjustment stems from that more than anything. If this wasn't my daily driver I probably would spend far too much time trying to fix it before I replaced it, but it probably does make sense to just replace it in the situation. As an aside I tested my old thermostat in a pot of hot water with a meat thermometer and it didn't open until 190 so I suspect that no matter what it was a good thing to replace that anyways. Thanks for the info on electric fans too, I had been pondering that option and read through a few thread on it, but wasn't sure how involved it truly was.

technocj- As for radiator flush I know the previous owner had done some pretty significant work to the coolant system withing the last 3 years and either had the radiator flushed or re-cored (he couldn't give me a straight answer) so while I'm not ruling that out it could for sure be an issue.