# Please double-check my car repair diagnosis **URL:** \ **Category:** Factual Questions\ **Created:** [September 29, 2020, 12:18am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779 "2020-09-29T00:18:07Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [September 29, 2020, 12:18am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/1 "2020-09-29T00:18:07Z")
2008 GMC Envoy 140K miles. While driving, the car pegs to the redline and Mrs Cad pulls off (I wasn’t in the car). I get there and there is coolant all over the engine compartment. I turn it on to make sure it still runs (it does) and coolant leaks out from somewhere. I get it home and once the engine cools I notice the reservoir level is the same. Ahh, open system so a leak somewhere (if that wasn’t obvious). I top off the radiator and even before I can start the car the coolant starts leaking out under the water pump. It lets off after a few seconds though. My diagnosis, blown seal on the water pump and replace it. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [September 29, 2020, 12:54am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/2 "2020-09-29T00:54:07Z")
Remove the floor mat on the driver’s side. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [September 29, 2020, 12:54am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/3 "2020-09-29T00:54:48Z")
Why do that? ---
**Author:** ![Si\_Amigo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/si_amigo/32/2877_2.png) [@Si\_Amigo](https://boards.straightdope.com/u/Si_Amigo)\ **Post date:** [September 29, 2020, 1:29am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/4 "2020-09-29T01:29:27Z")
Look for a pool of coolant. If there it may be the heater core leaking. Its what gets heat from the engine to the passengers. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [September 29, 2020, 1:35am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/5 "2020-09-29T01:35:52Z")
I will double check but pretty sure no coolant in the car and I saw coolant spraying out below the pump and there was coolant all over the engine compartment. Not sure a leaky heater core would do all that. ---
**Author:** ![california\_jobcase](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@california\_jobcase](https://boards.straightdope.com/u/california_jobcase)\ **Post date:** [September 29, 2020, 1:55am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/6 "2020-09-29T01:55:32Z")
> [@Saint\_Cad](#): > > My diagnosis, blown seal on the water pump and replace it. Replace the water pump and gasket, or just the gasket? You have to take off the pump to replace the gasket, so it will be easy enough to check the condition of the pump then. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [September 29, 2020, 1:56am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/7 "2020-09-29T01:56:54Z")
Might just be the gasket but with the mileage why not replace the pump too? ---
**Author:** ![MindsEye\_Watering](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mindseye_watering/32/3619_2.png) [@MindsEye\_Watering](https://boards.straightdope.com/u/MindsEye_Watering)\ **Post date:** [September 29, 2020, 2:05am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/8 "2020-09-29T02:05:11Z")
I suggest that you also check the coolant temperature sensor. I’ve had two of those blow out. ---
**Author:** ![california\_jobcase](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@california\_jobcase](https://boards.straightdope.com/u/california_jobcase)\ **Post date:** [September 29, 2020, 3:20am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/9 "2020-09-29T03:20:45Z")
That’s what I’d do. I just wasn’t sure which it your “replace it” meant. ---
**Author:** ![RivkahChaya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rivkahchaya/32/8919_2.png) [@RivkahChaya](https://boards.straightdope.com/u/RivkahChaya)\ **Post date:** [September 29, 2020, 4:08am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/10 "2020-09-29T04:08:59Z")
Replace any hose and hose clamp that has to be removed to get the the water pump. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [September 29, 2020, 4:28am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/11 "2020-09-29T04:28:26Z")
How long was it running at redline? I’m assuming you’re referring to the temperature gage, and not the tach. A leaky pump gasket wouldn’t cause a sudden spike in temp, but a blown head gasket can do that, and along with the temp increase, the cooling system pressure spikes, and the overpressure looks for a way out. In your case, it left via the pump gasket. So, you may want to do further tests (compression, coolant in oil, etc.) before going much farther. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [September 29, 2020, 4:31am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/12 "2020-09-29T04:31:50Z")
As I said in the OP I wasn’t riding in the car at the time. Mrs Cad realized it was on redline when the car dummy light went off. Pretty sure the head gasket is ok. No oil in the coolant. At least I hope the head gasket is ok. I’ll check the oil tomorrow. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [September 29, 2020, 10:33am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/13 "2020-09-29T10:33:01Z")
Sounds to me like a sound diagnosis. Replace the pump. I understand “blown seal on the water pump” to mean the shaft seal integral to the pump rather than to the pump gasket; this would be correct terminology. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [September 29, 2020, 10:35am UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/14 "2020-09-29T10:35:16Z")
For coolant under the hood and streaming from the water pump? Why on Earth look there? ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [September 29, 2020, 4:51pm UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/15 "2020-09-29T16:51:09Z")
> [@Gary\_T](#): > > I understand “blown seal on the water pump” to mean the shaft seal integral to the pump rather than to the pump gasket; this would be correct terminology. Thanks for the correction. Although it looks like the gasket I assume that failure is very rare compared to the seal on a 140K mile water pump, hence my plan to replace both. On a side note, I’m thinking of going with an AC Delco water pump. Any opinion on that and IIRC aren’t they the OEM manufacturer for 2008 GMCs? ---
**Author:** ![scabpicker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scabpicker/32/8268_2.png) [@scabpicker](https://boards.straightdope.com/u/scabpicker)\ **Post date:** [September 30, 2020, 1:35pm UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/16 "2020-09-30T13:35:25Z")
It does sound like you’ve diagnosed half of the issue at least, but I can’t figure out how a failing water pump would make it peg at redline, much less without the car accelerating. You may end up needing to diagnose that after replacing the pump. > [@Saint\_Cad](#): > > On a side note, I’m thinking of going with an AC Delco water pump. Any opinion on that and IIRC aren’t they the OEM manufacturer for 2008 GMCs? It shouldn’t make too much difference. A water pump wouldn’t be really complex to rebuild or manufacture. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [September 30, 2020, 1:37pm UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/17 "2020-09-30T13:37:28Z")
Just a guess but it lost over a gallon of coolant so I imagine that’s why it overheated. ---
**Author:** ![scabpicker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scabpicker/32/8268_2.png) [@scabpicker](https://boards.straightdope.com/u/scabpicker)\ **Post date:** [September 30, 2020, 1:59pm UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/18 "2020-09-30T13:59:06Z")
Hah, I think I misunderstood “pegs to the redline”. I was thinking you meant RPM, but you’re meaning the temp gauge. ---
**Author:** ![excavating\_for\_a\_mind](https://avatars.discourse-cdn.com/v4/letter/e/e8c25b/32.png) [@excavating\_for\_a\_mind](https://boards.straightdope.com/u/excavating_for_a_mind)\ **Post date:** [September 30, 2020, 2:15pm UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/19 "2020-09-30T14:15:55Z")
I think the OP hit the nail on the head with his diagnosis. Some of the terminology is a bit non-standard (“pegs the redline” often refers to the tachometer, not the temperature gauge; others have conflated the term “seal” with “gasket”), if you understand what the OP is about, it is a pretty simple diagnosis. IME, water pumps will usually last between 100,000 and 200,000 miles. It is rare for one on a modern car to fail very much below 100,000 miles and one lasting over 200,000 miles is very rare. On my daily driver, the routine maintenance calls for the timing belt to be replaced every 100,000 miles, but makes no mention of replacing the water pump as routine maintenance. I’ve owned the vehicle for over 15 years (it had about 90,000 on it when I bought it). Soon after I bought it, I had the timing belt replaced as routine maintenance and was advised to have the water pump replaced at the same time, since the water pump must be removed to replace the timing belt. Since the water pump only costs around $50 and repairing a failed water pump would cost about $200 (not to mention being stranded when it happens), I did it. I replace all hoses at that time, too. About 8 years later, it was time for another timing belt, so, again, I had the water pump and hoses replaced when the timing belt was replaced. As I have said, I’ve driven the car for 15 years, put about 130,000 miles on it myself (220,000+ total) and have never had a water pump or hose failure. That’s the value of preventative maintenance. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [October 8, 2020, 10:13pm UTC](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779/20 "2020-10-08T22:13:12Z")
OMG why can’t anything be easy. Trying to loosen the fan clutch nut and _there are no bolts in the pulley for me to grab_. So what do I do now? [Next page](https://boards.straightdope.com/t/please-double-check-my-car-repair-diagnosis/921779.md?page=2)