I replaced my water pump a few months ago and ever since I have had fluctuating temps. The new pump is a bosch from pepboys and had a shroud on the impeller and the old unit did not, I also noticed the new one was harder to turn than the old one but that is to be expected. My temp used to set right around 188-194 and now driving down the interstate at 70 I get swings from 188-222 today. It would go up pretty fast and come back down to around 200-205 or so but I cant help but theink its the new pump. I may try a new radiator cap too but what does everyone think?

--- Update to the previous post...

The old pump worked great but I did a coolant flush and it leaked from the weep hole afterwards and is the reason it was replaced. The o-ring was also flat but I dont believe it leaked, if I were to put a new o-ring on it would it fix the leak from the weep hole? The bearing and impeller feel tight and spin freely.

I had to get a new one a couple months back and it had a shroud too. Thinking by shroud you mean a little chinese hat thing with a hole in the center over the impeller? I didn't notice any difference in temps.

Like this

Ya, thats what it looks like. I never noticed any swinging before other than when I had the high idle box and got low temps.

Took that junk back to pepboys and bought one from napa without that little impeller cover and it seems to have helped. I havent been able to get it on the road yet because my tags havent come in the mail yet and I dont want another run-in with the po po. I also got a new radiator cap but they offered two, one vented and one not, I got the one not vented but didnt really know what that meant. Do we have vented radiator caps?

I think the vented ones are the ones with the lever on them that allow you to vent it manually. This is so when the engine is hot you can lift the lever and it blows the pressure into the reservoir until it has no pressure and then you can safely take the cap off. Radiator caps seal off the radiator with the rubber thing on the bottom with a spring that gets pushed back at 15lbs or whatever the pressure is. So when the pressure gets to 15lbs the water can push the seal out of the way and move out to the reservoir. The lever works by simply pulling the seal up, simulating high pressure relief.

They had that one too but here are the two they offered, they look identical but the vented one is $1 more. http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?A=BK_7031699_0329911717&An=599001+101998+50022+2022010&Ar=AND(P_RecType%3aA) http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?A=BK_7031698_0314019073&An=599001+101998+50022+2022010&Ar=AND(P_RecType%3aA)

Those links don't work. NAPA uses a setup that works on your computer only as you go through the selection process. Nevertheless, I don't know what else it could be. If the cap doesn't vent then it wouldn't regulate pressure. I have no idea what they mean.

Well between the new Napa water pump and ventless radiator cap my temp fluctuations have stopped.

Even though my last oil sample said zero coolant in oil I have a bad feeling my head gasket may have bit the bullet. The new water pump and radiator cap fixed my temp fluctuation but I checked my coolant 2 days now and I have a little milky sobstance on the spring in the radiator cap. You can see the white stuff on my finger tip. The coolant isnt milky at all, its crystal clear but this little milky stuff along with the small puff of white smoke on startup.

is it oily at all?

No, just that white stuff on the spring. I just put my old cap back in and will check again tomorrow.

not oily is a good sign. Maybe just something left over from all the flushing.

I checked the old radiator cap today and no milky stuff on the spring so maybe it was just nasty stuff on the spring from the factory.

My swinging temps are back so I changed the t stat with no change, they are from 190-220. I just took the water pump off and its got some kind of crud built up on the impeller that I have never seen with my other pumps. It has had green coolant in it but I recently changed to the red and distilled water. here is the old pump and wonder if I should change to a different coolant too?

I replaced my water pump a few months ago and ever since I have had fluctuating temps. The new pump is a bosch from pepboys and had a shroud on the impeller and the old unit did not, I also noticed the new one was harder to turn than the old one but that is to be expected. My temp used to set right around 188-194 and now driving down the interstate at 70 I get swings from 188-222 today. It would go up pretty fast and come back down to around 200-205 or so but I cant help but theink its the new pump. I may try a new radiator cap too but what does everyone think?

I just installed the exact same water pump from pepboyz ..... no issues with fluctuating temps FYI

I guess I have bigger problems because the new pump is doing the same thing.:banghead:

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I put a 180 cummins t stat in it and now it floats between 180-190 or so but will go up higher for a split second. My ultra gauge updates every 2 seconds and it will say 183 and then 203 and then back down to 185 in 4 seconds but my factroy gauge doesnt move while its doing this. My factory gauge is floating between 180-190 or so though. There is no water in oil or vise versa but i fear its the headgasket.

I guess I have bigger problems because the new pump is doing the same thing.:banghead:

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I put a 180 cummins t stat in it and now it floats between 180-190 or so but will go up higher for a split second. My ultra gauge updates every 2 seconds and it will say 183 and then 203 and then back down to 185 in 4 seconds but my factroy gauge doesnt move while its doing this. My factory gauge is floating between 180-190 or so though. There is no water in oil or vise versa but i fear its the headgasket.

Cant imagine its swinging 40 deg in 4 seconds (183->203->183)

Something wrong with the sensor ?

Cant you buy a coolant sampler to test for gasket failure in coolant .....

I dont know, never heard of that before. I thought it might be the sensor too but its stays in the operating range, I figured if the sensor was bad it might read really low or really high not almost right. Mike said maybe fan clutch time?

My father-in-law said I need to rod my radiator but I think I might just get a new one. How odes this one look?

http://www.yourautocoolingsource.com/site/823209/product/CU1553 or

http://www.fastradiator.com/ViewProduct.asp?ModelNumber=FAS-1553

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Just spoke with a radiator shop and they said $65 to clean it out so I guess I will try that.

Now if you keep you coolant changed / flushed every 30K this wouldn't be happening...